Diving in OOP (Part 1) : Polymorphism and Inheritance(Early Binding/Compile Time Polymorphism).


Introduction

I have been writing a lot about advanced topics like MVC, Entity Framework, Repository Patterns etc, my priority always remains to cover the topic as a whole, so that a reader does not have to search for missing links anywhere else. This article will cover almost every OOPS concept that a novice/beginner developer may hunt for, and not only beginners, the article’s purpose is to be helpful to experienced professionals who may need to brush-up on their concepts or who prepare for interviews.
I will take the topics in a manner that we cover them in a simple, straightforward way giving code snippets as example wherever needed. We’ll take C# as our programming language throughout our readings.
We’ll play with tricky questions and not go for enough theory. For theory you can refer MSDN.
Pre-requisites
Since this is the first part of the series, my readers should have basic knowledge of C# and should be aware of OOP concepts and terminology.
Note: Each and every code snippet written in this article is tried and tested.

OOPS

1. What is OOPS and what is advantage of OOP?

OOP stands for “Object-Oriented Programming.” Remember, it’s OOP not OOPS,’S’ may stand for system, synopsis, structure etc. It is a programming approach entirely based on objects, instead of just functions and procedures like in procedural languages. It is like a programming language model organized around objects rather than “actions” and data rather than logic. An “object” in an OOP language refers to a specific type, or “instance,” of a class. Each object has a structure exactly similar to other objects in a class, but can have individual properties/values. An object can also invoke methods, specific to that object
OOP makes it easier for developers to structure and organize software programs. Individual objects can be modified without affecting other aspects of the program therefore it is also easier to update and change programs written in object-oriented languages. Since the nature of software programs have grown larger over the years, OOP has made developing these large programs more manageable and readable.

2. What are OOP Concepts?

Following are OOP concepts explained in brief, we’ll take the topics in detail.
  1. Data Abstraction: Data Abstraction is a concept in which the internal and superfluous details of the implementation of a logic is hidden from an end user(who is using the program) .A user can use any of the data and method from the class without knowing about how this is created or what is the complexity behind it. In terms of a real world example, when we drive a bike and change the gears we don’t have to care about how internally its working, like how liver is pulled or how chain is set.
  2. Inheritance: Inheritance is most popular Concept in OOP’s .This provides a developer an advantage called reusability of code. Suppose a class is written having functions with specific logic, then we can derive that class into our newly created class and we don’t have to write the logic again for derived class functions, we can use them as it is.
  3. Data Encapsulation: Wrapping up of member data and member functions of a class in a single unit is called encapsulation. The visibility of the member functions,data members is set via access modifiers used in class.
  4. Polymorphism: Poly means many and morphism means many function The Concepts Introduces in the form of Many behaviours of an object.
  5. Message Communication: Message Communication means when an object passes the call to method of class for execution.
OK, we covered lots of theory, now it’s time for action. I hope that will be interesting. We’ll cover the topics in a series as follows,
  1. Diving in OOP (Day 1): Polymorphism and Inheritance(Early Binding/Compile Time Polymorphism)
  2. Diving in OOP (Day 2): Polymorphism and Inheritance (Inheritance)
  3. Diving in OOP (Day 3): Polymorphism and Inheritance (Dynamic Binding/Run Time Polymorphism)
  4. Diving in OOP (Day 4): Polymorphism and Inheritance (All about Abstarct classes in C#)
  5. Diving in OOP (Day 5): All about access modifiers in C# (Public/Private/Protected/Internal/Sealed/Constants/Readonly Fields)
  6. Diving in OOP (Day 6): Understanding Enum in C# (A Practical Approach)
  7. Diving into OOP (Day 7): Properties in C# (A Practical Approach)
  8. Diving into OOP (Day 8): Indexers in C# (A Practical Approach)
  9. Diving into OOP (Day 9): Understanding Events in C# (An Insight)

3. Polymorphism:

In this article we will cover almost all the scenarios of compile type polymorphism, the use of params keyword in detail, and case study or hands on to different possible combinations of the thoughts coming to our mind while coding.

Method Overloading or Early Binding or Compile Time Polymorphism

  1. Let’s create a simple console application named InheritanceAndPolymorphism, and add a class namedOverload.cs and add three methods named DisplayOverload having varied parameters as follows,

    Overload.cs

    public class Overload
        {
            public void DisplayOverload(int a){
                System.Console.WriteLine("DisplayOverload " + a);
            }
            public void DisplayOverload(string a){
                System.Console.WriteLine("DisplayOverload " + a);
            }
            public void DisplayOverload(string a, int b){
                System.Console.WriteLine("DisplayOverload " + a + b);
            }
        }

    In the main method in Program.cs file, add the following code,

    Program.cs

    class Program
        {
            static void Main(string[] args)
            {
                Overload overload = new Overload();
                overload.DisplayOverload(100);
                overload.DisplayOverload("method overloading");
                overload.DisplayOverload("method overloading", 100);
                Console.ReadKey();
            }
        }
Now when you run the application, the output is,

Output

DisplayOverload 100
DisplayOverload method overloading
DisplayOverload method overloading100
The class Overload contains three methods named DisplayOverload, they only differ in the datatype of the parameters they consist of. In C# we can have methods with the same name, but the datatypes of their parameters should differ. This feature of C# is called method overloading. Therefore, we need not to remember lots of method names if a method differs in behavior, only providing different parameters to the methods can call a method individually.
Point to remember: C# recognizes the method by its parameters and not by its name.
A signature signifies the full name of the method. So the name of a method or its signature is the original method name + the number and data types of its individual parameters.
If we run project using following code,
public void DisplayOverload() { }
     public int DisplayOverload(){ }
We certainly get a compile time error as,
Error: Type ‘InheritanceAndPolymorphism.Overload’ already defines a member called ‘DisplayOverload’ with the same parameter types
Here we had two functions who differ only in the data type of the value that they return, but we got a compile time error, therefore, another point to remember comes,
 
Point to remember: The return value/parameter type of a method is never the part of method signature if the names of the methods are same. So this is not polymorphism.
If we run the project using following code,
static void DisplayOverload(int a)  {   }
public void DisplayOverload(int a) {   }
public void DisplayOverload(string a){  }
We again get a compile time error,
Error: Type ‘InheritanceAndPolymorphism.Overload’ already defines a member called ‘DisplayOverload’ with the same parameter types
Can you differentiate with the modification done in the above code, we now have two DisplayOverload methods, that accept an int (integer). The only difference is that one method is marked static. Here the signature of the methods will be considered same as modifiers such as static are also not considered to be a part of method signature.
 
Point to remember: Modifiers such as static are not considered as part of method signature.
If we run the program as per following code, considering the method signature is different now,
private void DisplayOverload(int a) {   }

private void DisplayOverload(out int a)
{
a = 100;
}

private void DisplayOverload(ref int a) { }

We again get a compile time error,
Error: Cannot define overloaded method ‘DisplayOverload’ because it differs from another method only on ref and out
The signature of a method not only consists of the data type of the parameter but also the type/kind of parameter such as ref or out etc. Method DisplayOverload takes an int with different access modifiers i.e. out/ref etc, the signature on each is different.
 
Point to remember: The signature of a method consists of its name, number and types of its formal parameters. The return type of a function is not part of the signature. Two methods can not have the same signature and also non-members cannot have the same name as members.

4. Role of Params Parameter in Polymorphism

A method can be called by four different types of parameters.
  1. pass by value,
  2. Pass by reference,
  3. As an output parameter,
  4. Using parameter arrays.
As explained earlier the parameter modifier is never the part of method signature. Now let’s focus on Parameter Arrays.
A method declaration means creating a separate declaration space in memory. So anything created will be lost at the end of the method.
Running following code,
public void DisplayOverload(int a, string a)  {   }

public void Display(int a)
{
string a;
}

Results in compile time error,
 
Error1: The parameter name ‘a’ is a duplicate
Error2: A local variable named ‘a’ cannot be declared in this scope because it would give a different meaning to ‘a’, which is already used in a ‘parent or current’ scope to denote something else
 
Point to remember: Parameter names should be unique. And also we can not have a parameter name and a declared variable name in the same function as same.
In the case of pass by value, the value of the variable is passed and in the case of ref and out, the address of the reference is passed.
When we run the following code,

Overload.cs

public class Overload
    {
        private string name = "Akhil";

public void Display()
{
Display2(ref name, ref name);
System.Console.WriteLine(name);
}

private void Display2(ref string x, ref string y)
{
System.Console.WriteLine(name);
x = Akhil 1″;
System.Console.WriteLine(name);
y = Akhil 2″;
System.Console.WriteLine(name);
name = Akhil 3″;
}
}

Program.cs

class Program
    {
        static void Main(string[] args)
        {
            Overload overload = new Overload();
            overload.Display();
            Console.ReadKey();
        }
    }
We get out put as,

Output

Akhil
Akhil 1
Akhil 2
Akhil3

We are allowed to pass the same ref parameter as many times as we want. In the method Display the string name has a value of Akhil. Then by changing the string x to Akhil1, we are actually changing the string name to Akhil1 as name is passed by reference. Variables x and name refer to the same string in memory. Changing one changes the other. Again changing y also changes name variable as they refer to the same string anyways. Thus variables x, y and name refer to the same string in memory.
When we run the following code,

Overload.cs

public class Overload
    {
        public void Display()
        {
            DisplayOverload(100, "Akhil", "Mittal", "OOP");
            DisplayOverload(200, "Akhil");
            DisplayOverload(300);
        }

private void DisplayOverload(int a, params string[] parameterArray)
{
foreach (string str in parameterArray)
Console.WriteLine(str + + a);
}
}

Program.cs

class Program
    {
        static void Main(string[] args)
        {
            Overload overload = new Overload();
            overload.Display();
            Console.ReadKey();
        }
    }
We get output,

Output

Akhil 100
Mittal 100
OOP 100
Akhil 200
We will often get into a scenario where we would like to pass n number of parameters to a method. Since C# is very particular in parameter passing to methods, if we pass an int where a string is expected, it immediately breaks down. But C# provides a mechanism for passing n number of arguments to a method,
we can achieve it with the help ofparams keyword.
 
Point to remember: This params keyword can only be applied to the last argument of the method. So the n number of parameters can only be at the end.
In the case of method DisplayOverload, the first argument has to be an integer, the rest can be from zero to an infinite number of strings.
If we add a method like ,
private void DisplayOverload(int a, params string[] parameterArray, int b) {  }
We get a compile time error as,
 
Error: A parameter array must be the last parameter in a formal parameter list
Thus is is proved that params keyword will be the last parameter in a method, this is already stated in the latest point to remember.

Overload.cs

public class Overload
    {
        public void Display()
        {
            DisplayOverload(100, 200, 300);
            DisplayOverload(200, 100);
            DisplayOverload(200);
        }

private void DisplayOverload(int a, params int[] parameterArray)
{
foreach (var i in parameterArray)
Console.WriteLine(i + + a);
}

}

Program.cs

class Program
    {
        static void Main(string[] args)
        {
            Overload overload = new Overload();
            overload.Display();
            Console.ReadKey();
        }
    }
When we run the code we get,
200 100
300 100
100 200
Therefore,
 
Point to Remember: C# is very smart to recognize if the penultimate argument and the params have the same data type.
The first integer is stored in the variable a, the rest are made part of the array parameterArray.
private void DisplayOverload(int a, params string[][] parameterArray)  {     }

private void DisplayOverload(int a, params string[,] parameterArray) { }

For the above written code, we again get a compile time error and a new point to remember as well,
 
Error:The parameter array must be a single dimensional array
Point to remember: same as error above.
The data type of the params argument must be a single dimensional array. Therefore [ ][ ]
is allowed but not [,]. We also not allowed to combine the params keyword with ref or out.

Overload.cs

public class Overload
    {
        public void Display()
        {
            string[] names = {"Akhil", "Ekta", "Arsh"};
            DisplayOverload(3, names);
        }

private void DisplayOverload(int a, params string[] parameterArray)
{
foreach (var s in parameterArray)
Console.WriteLine(s + + a);
}

}

Program.cs

class Program
    {
        static void Main(string[] args)
        {
            Overload overload = new Overload();
            overload.Display();
            Console.ReadKey();
        }
    }

Output

Akhil 3
Ekta 3
Arsh 3
We are, therefore, allowed to pass a string array instead of individual strings as arguments. Here, names is a string array which has been initialized using the short form. Internally when we call the function DisplayOverload, C# converts the string array into individual strings.

Overload.cs

public class Overload
    {
        public void Display()
        {
           string [] names = {"Akhil","Arsh"};
           DisplayOverload(2, names, "Ekta");
        }

private void DisplayOverload(int a, params string[] parameterArray)
{
foreach (var str in parameterArray)
Console.WriteLine(str + + a);
}

}

Program.cs

class Program
    {
        static void Main(string[] args)
        {
            Overload overload = new Overload();
            overload.Display();
            Console.ReadKey();
        }
    }

Output

Error: The best overloaded method match for ‘InheritanceAndPolymorphism.Overload.DisplayOverload(int, params string[])’ has some invalid arguments
Error:Argument 2: cannot convert from ‘string[]’ to ‘string’
So, we got two errors. 
For the above mentioned code, C# does not permit mix and match. We assumed that the last string “Ekta” would be added to the array of strings names or convert names to individual strings and then add the string “Ekta” to it. Quite logical.
Internally before calling the function DisplayOverload, C# accumulates all the individual parameters and converts them into one big array for the params statement.

Overload.cs

public class Overload
    {
        public void Display()
        {
            int[] numbers = {10, 20, 30};
            DisplayOverload(40, numbers);
            Console.WriteLine(numbers[1]);
        }

private void DisplayOverload(int a, params int[] parameterArray)
{
parameterArray[1] = 1000;
}

}

Program.cs

class Program
    {
        static void Main(string[] args)
        {
            Overload overload = new Overload();
            overload.Display();
            Console.ReadKey();
        }
    }

Output

1000
We see that the output produced is the proof of concept. The member parameterArray[1] of array has an initial value of 20 and in the method DisplayOverload, we changed it to 1000. So the original value changes, this shows that the array is given to the method DisplayOverload, Hence proved.

Overload.cs

public class Overload
    {
        public void Display()
        {
            int number = 102;
            DisplayOverload(200, 1000, number, 200);
            Console.WriteLine(number);
        }

private void DisplayOverload(int a, params int[] parameterArray)
{
parameterArray[1] = 3000;
}

}

Program.cs

class Program
    {
        static void Main(string[] args)
        {
            Overload overload = new Overload();
            overload.Display();
            Console.ReadKey();
        }
    }

Output

102
In the above mentioned scenario C# creates an array containing 1000 102 and 200. We now change the second member of array to 3000 which has nothing to do with the variable number. As DisplayOverload has no knowledge of number, so how can DisplayOverload change the value of the int number? Therefore it remains the same.

Overload.cs

public class Overload
    {
        public void Display()
        {
            DisplayOverload(200);
            DisplayOverload(200, 300);
            DisplayOverload(200, 300, 500, 600);
        }

private void DisplayOverload(int x, int y)
{
Console.WriteLine(The two integers “ + x + + y);
}

private void DisplayOverload(params int[] parameterArray)
{
Console.WriteLine(parameterArray”);
}

}

Program.cs

class Program
    {
        static void Main(string[] args)
        {
            Overload overload = new Overload();
            overload.Display();
            Console.ReadKey();
        }
    }

Output

parameterArray
The two integers 200 300
parameterArray
Now we’ll talk about method overloading. C# is extremely talented though partial. It does not appreciate the paramsstatement and treats it as a stepchild. When we invoke DisplayOverload only with one integer, C# can only call theDisplayOverload that takes a params as a parameter as it matches only one int. An array can contain one member too. The fun is with the DisplayOverload that is called with two ints now. So here we have a dilemma. C# can call theparams DisplayOverload or DisplayOverload with the two ints. As discussed earlier, C# treats the params as a second class member and therefore chooses the DisplayOverload with two ints. When there are more than two ints like in the third method call, C# is void of choice but to grudgingly choose the DisplayOverload with the params. C# opts for the params as a last resort before flagging an error.
Now a bit tricky example, yet important,

Overload.cs

public class Overload
    {
        public static void Display(params object[] objectParamArray)
        {
            foreach (object obj in objectParamArray)
            {
                Console.Write(obj.GetType().FullName + " ");
            }
            Console.WriteLine();

}
}

Program.cs

class Program
    {
        static void Main(string[] args)
        {
            object[] objArray = { 100, "Akhil", 200.300 };
            object obj = objArray;
            Overload.Display(objArray);
            Overload.Display((object)objArray);
            Overload.Display(obj);
            Overload.Display((object[])obj);
            Console.ReadKey();

}
}

Output

System.Int32 System.String System.Double
System.Object[]
System.Object[]
System.Int32 System.String System.Double
In the first instance we are passing the method Display an array of object that looks like object. Since all the classes are derived from a common base class object, we can do that. The method Display gets an array of objectsobjectParamArray. In the foreach object class has a method named GetType that returns an object that looks like Type, which too has a method named FullName that returns the name of the type. Since three different types displayed. In the second method call of Display we are casting objArray to an object. Since there is no conversion available from converting an object to an object array i.e. object [ ], so only a one element object [ ] is created. It’s the same case in the third invocation and the last explicitly casts to an object array.
For proof of concept,

Overload.cs

public class Overload
    {
        public static void Display(params object[] objectParamArray)
        {
            Console.WriteLine(objectParamArray.GetType().FullName);
            Console.WriteLine(objectParamArray.Length);
            Console.WriteLine(objectParamArray[0]);

}
}

Program.cs

class Program
    {
        static void Main(string[] args)
        {
            object[] objArray = { 100, "Akhil", 200.300 };
            Overload.Display((object)objArray);
            Console.ReadKey();
        }
    }

Output

System.Object[]
1
System.Object[]

5. Conclusion

In this article of our Diving in OOP series we learnt about compile time polymorphism, it is also called early binding or method overloading. We catered most of the scenarios specific to polymorphism.We also learned about the use of powerful params keyword and its use in polymorphism.
To sum up lets list down all the point to remembers once more,
  1. C# recognizes the method by its parameters and not by its name.
  2. The return value/parameter type of a method is never the part of method signature if the names of the methods are same. So this is not polymorphism.
  3. Modifiers such as static are not considered as part of method signature.
  4. The signature of a method consists of its name, number and types of its formal parameters. The return type of a function is not part of the signature. Two methods can not have the same signature and also non-members cannot have the same name as members.
  5. Parameter names should be unique. And also we can not have a parameter name and a declared variable name in the same function as same.
  6. In case of pass by value, the value of the variable is passed and in the case of ref and out, the address of the reference is passed.
  7. This params keyword can only be applied to the last argument of the method.So the n number of parameters can only be at the end.
  8. C# is very smart to recognize if the penultimate argument and the params have the same data type.
  9. Parameter array must be a single dimensional array.
In upcoming articles we’ll cover topics in the same fashion.  Happy Coding.

Read more:

Other Series

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For more informative articles visit my Blog.

For more technical articles you can reach out to CodeTeddy.

 

 

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Complete End to End CRUD Operations Using Knockout.JS and EntityFramework 5 in MVC4 Application


I) Introduction

I have been browsing multiple sites to check if I could find a complete end to end tutorial or article upon CRUD operations using Knockout.JS and MVC 4. Unfortunately, all the ones I found were incomplete or had too short an explanation. In my last article we learned CRUD in ASP.NET web forms using MVC and EntityFramework. This article is the continuation to the same series. This article will be a kind of tutorial to explain how we can set up a Knockout.JS environment in an MVC4 application that is also capable of performing CRUD operations.

II) Our Road-Map

We’ll stick to our agenda of Learning Knockout.JS as follows,

III) Part2: Complete end to end CRUD operations using Knockout.JS and Entity Framework in MVC4 application

We’ll continue to discuss KO step by step in this article
  1. Creating an MVC application.
  2. Creating CRUD action methods using Entity Framework 5.
  3. Perform CRUD operations using MVC4 and Entity Framework 5
  4. Adding Knockout.JS to our MVC application.
  5. Perform CRUD operation using KO in our MVC 4 application.
Before we start, not going very deep into theory I would like to give an introduction to MVC,Entity Framework and Knockout.

IV) MVC

Model: The business entity on which the overall application operates. Many applications use a persistent storage mechanism (such as a database) to store data. MVC does not specifically mention the data access layer because it is understood to be encapsulated by the Model.
View: The user interface that renders the model into a form of interaction.
Controller: Handles a request from a view and updates the model that results a change in Model’s state.
To implement MVC in .NET we need mainly three classes (View, Controller and the Model).

V) Entity Framework

Let’s have a look on standard definition of Entity Framework given by Microsoft:

“The Microsoft ADO.NET Entity Framework is an Object/Relational Mapping (ORM) framework that enables developers to work with relational data as domain-specific objects, eliminating the need for most of the data access plumbing code that developers usually need to write. Using the Entity Framework, developers issue queries using LINQ, then retrieve and manipulate data as strongly typed objects. The Entity Framework’s ORM implementation provides services like change tracking, identity resolution, lazy loading, and query translation so that developers can focus on their application-specific business logic rather than the data access fundamentals.

In a simple language, Entity framework is an Object/Relational Mapping (ORM) framework. It is an enhancement to ADO.NET, an upper layer to ADO.NET that gives developers an automated mechanism for accessing & storing the data in the database.
Hope this gives a glimpse of an ORM and EntityFramework.

VI) Knockout.JS

Knockout.JS (KO) is basically a JS library that enables Declarative Bindings using an ‘Observable’ View Model on the client (browser) following observer pattern approach, enabling UI to bind and refresh itself automatically whenever the data bound is modified. Knockout.JS provides its own templating pattern that helps us to bind our view model data easily. KO works on MVVM pattern i.e. Model-View-View Model.
As the architecture is shown, Views interact with View Models in a two way binding manner i.e. when the model is changed it view updates itself and when view is updated, the model updates itself instantaneously.
KO provides 3 most important features like,

 

The whole idea of KO derives from these three major functionalities. KO also helps in developing Single page applications (SPA’s).SPA’s are out of the box new way of developing rich internet applications(RIA’s) in todays era.

VII) Application Architecture

The architecture is very much self explanatory. The application works on client-server model, where our MVC application or Web API application (not covered in this tutorial) will interact with EntityFramework layer on server side. Entity Framework layer will be responsible for data transactions with data base.
On clientside we have HTML templates which will communicate with server through Ajax calls and the templates will be bind to data via JSON objects through knockout observables (already discussed in first part).

VIII) MVC Application

1. Step1: Create a data base named LearningKO and add a table named student to it, script of the table is as follows,
USE [LearningKO]
GO
/****** Object:  Table [dbo].[Student]    Script Date: 12/04/2013 23:58:12 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Student](
 [StudentId] [nvarchar](10) NOT NULL,
 [FirstName] [nvarchar](50) NULL,
 [LastName] [nvarchar](50) NULL,
 [Age] [int] NULL,
 [Gender] [nvarchar](50) NULL,
 [Batch] [nvarchar](50) NULL,
 [Address] [nvarchar](50) NULL,
 [Class] [nvarchar](50) NULL,
 [School] [nvarchar](50) NULL,
 [Domicile] [nvarchar](50) NULL,
CONSTRAINT [PK_Student] PRIMARY KEY CLUSTERED
(
 [StudentId] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
INSERT [dbo].[Student] ([StudentId], [FirstName], [LastName], [Age], [Gender], [Batch], [Address], [Class], [School], [Domicile]) VALUES (N'1', N'Akhil', N'Mittal', 28, N'Male', N'2006', N'Noida', N'Tenth', N'LFS', N'Delhi')
INSERT [dbo].[Student] ([StudentId], [FirstName], [LastName], [Age], [Gender], [Batch], [Address], [Class], [School], [Domicile]) VALUES (N'2', N'Parveen', N'Arora', 25, N'Male', N'2007', N'Noida', N'8th', N'DPS', N'Delhi')
INSERT [dbo].[Student] ([StudentId], [FirstName], [LastName], [Age], [Gender], [Batch], [Address], [Class], [School], [Domicile]) VALUES (N'3', N'Neeraj', N'Kumar', 38, N'Male', N'2011', N'Noida', N'10th', N'MIT', N'Outside Delhi')
INSERT [dbo].[Student] ([StudentId], [FirstName], [LastName], [Age], [Gender], [Batch], [Address], [Class], [School], [Domicile]) VALUES (N'4', N'Ekta', N'Mittal', 25, N'Female', N'2005', N' Noida', N'12th', N'LFS', N'Delhi')
  • Step2: Open your Visual Studio (Visual Studio Version should be greater than or equal to 12) and add an MVC Internet application,


 
 
I have given it a name “KnockoutWithMVC4”.
  • Step3: You’ll get a full structured MVC application with default Home controller in the Controller folder. By default the entity framework is downloaded as a package inside application folder, but if not you can add entity framework package by right click the project, select manage nugget packages and search and install Entity Framework,




  • 4. Step 4: Right click project file, select add new item and add ADO.NET entity data model. Follow the steps in the wizard as shown below,



    Generate the model from the data base, select your server and LearningKO database name, the connection string will automatically be added to your Web.Config, name that connection string as LearningKOEntities.

    Select tables to be added to the model. In our case it’s Student Table.


  • Step5: Now add a new controller to the Controller folder, right click controller folder and add a controller named Student. Since we have already created our Datamodel, we can choose for an option where CRUD actions are created by chosen Entity Framework Datamodel,


 
 
  • Name your controller as StudentController,
  • from Scaffolding Options, select “MVC controller with read/write actions and views, using Entity Framework”.
  • Select Model class as Student, that lies in our solution.
  • Select Data context class as LearningKOEntities that is added to outr solution when we added EF data model.
  • Select Razor as rendering engine for views.
  • Click Advanced options, Select Layout or master page and select _Layout.cshtml from the shared folder.
  • Step6: We see out student controller prepared with all the CRUD operation actions as shown below,
    7. using System;
    8. using System.Collections.Generic;
    9. using System.Data;
    10. using System.Data.Entity;
    11. using System.Linq;
    12. using System.Web;
    13. using System.Web.Mvc;
    14. 
    15. namespace KnockoutWithMVC4.Controllers
    16. {
    17.     public class StudentController : Controller
    18.     {
    19.         private LearningKOEntities db = new LearningKOEntities();
    20. 
    21.         //
    22.         // GET: /Student/
    23. 
    24.         public ActionResult Index()
    25.         {
    26.             return View(db.Students.ToList());
    27.         }
    28. 
    29.         //
    30.         // GET: /Student/Details/5
    31. 
    32.         public ActionResult Details(string id = null)
    33.         {
    34.             Student student = db.Students.Find(id);
    35.             if (student == null)
    36.             {
    37.                 return HttpNotFound();
    38.             }
    39.             return View(student);
    40.         }
    41. 
    42.         //
    43.         // GET: /Student/Create
    44. 
    45.         public ActionResult Create()
    46.         {
    47.             return View();
    48.         }
    49. 
    50.         //
    51.         // POST: /Student/Create
    52. 
    53.         [HttpPost]
    54.         [ValidateAntiForgeryToken]
    55.         public ActionResult Create(Student student)
    56.         {
    57.             if (ModelState.IsValid)
    58.             {
    59.                 db.Students.Add(student);
    60.                 db.SaveChanges();
    61.                 return RedirectToAction("Index");
    62.             }
    63. 
    64.             return View(student);
    65.         }
    66. 
    67.         //
    68.         // GET: /Student/Edit/5
    69. 
    70.         public ActionResult Edit(string id = null)
    71.         {
    72.             Student student = db.Students.Find(id);
    73.             if (student == null)
    74.             {
    75.                 return HttpNotFound();
    76.             }
    77.             return View(student);
    78.         }
    79. 
    80.         //
    81.         // POST: /Student/Edit/5
    82. 
    83.         [HttpPost]
    84.         [ValidateAntiForgeryToken]
    85.         public ActionResult Edit(Student student)
    86.         {
    87.             if (ModelState.IsValid)
    88.             {
    89.                 db.Entry(student).State = EntityState.Modified;
    90.                 db.SaveChanges();
    91.                 return RedirectToAction("Index");
    92.             }
    93.             return View(student);
    94.         }
    95. 
    96.         //
    97.         // GET: /Student/Delete/5
    98. 
    99.         public ActionResult Delete(string id = null)
    100.         {
    101.             Student student = db.Students.Find(id);
    102.             if (student == null)
    103.             {
    104.                 return HttpNotFound();
    105.             }
    106.             return View(student);
    107.         }
    108. 
    109.         //
    110.         // POST: /Student/Delete/5
    111. 
    112.         [HttpPost, ActionName("Delete")]
    113.         [ValidateAntiForgeryToken]
    114.         public ActionResult DeleteConfirmed(string id)
    115.         {
    116.             Student student = db.Students.Find(id);
    117.             db.Students.Remove(student);
    118.             db.SaveChanges();
    119.             return RedirectToAction("Index");
    120.         }
    121. 
    122.         protected override void Dispose(bool disposing)
    123.         {
    124.             db.Dispose();
    125.             base.Dispose(disposing);
    126.         }
    127.     }
    128. }


  • 7. Step7: Open App_Start folder and, change the name of controller from Home to Student,

 

the code will become as,
public static void RegisterRoutes(RouteCollection routes)
        {
            routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

routes.MapRoute(
name: Default”,
url: {controller}/{action}/{id}”,
defaults: new { controller = Student”, action = Index”, id = UrlParameter.Optional }
);
}

 

  • Step8: Now press F5 to run the application, and you’ll see the list of all students we added in to table Student while creating it is displayed. Since the CRUD operations are automatically written, we have action results for display list and other Edit, Delete and Create operations. Note that views for all the operations are created in Views Folder under Student Folder name.
  • Now you can perform all the operations on this list.


    Since I have not provided any validation checks on model or creating an existing student id, the code may break, so I am calling Edit Action in create when we find that id already exists,

    Now create new student ,

    We see that the student is created successfully and added to the list,

    In data base,

    Similarly for Edit,

    Change any field and press save.The change will be reflected in the list and data base,

    For Delete,

    Student Deleted.
    And in database,

    So, that’s it, our first job is completed i.e. to create an MVC application, and perform CRUD operations using Entity Framework 5. You can see that until now we have not written a single line of code. Yes that’s the magic of MVC and EF. Cheers!

    IX) Knockout Application

    Our first job is well done,now moving on to our primary target, i.e. KO. Since KO depends largely on MVVM pattern, we’ll take MVVM at client side, and use our controller to be as same just modified little bit for returning JSON logic. You can learn about MVVM pattern and KO theory in first part of this article series.

    1. Step1:JQuery and Knockout.js files are very important to be in the solution’s script folder. Check to them and if you do not find them, then add the packages for jQuery and Knockout, in the same fashion as you added Entity Framework.Right click project, select “Manage nugget packages” and search for jQuery then install it , then search for knockout package and install it,

    2. Step2: Right click Scripts folder and a folder named ViewModel.Add four js files to that folder, and name them as CreateVM.jsEditVM.jsDeleteVM.js and StudentListVM.js respectively. These are View Model files added to communicate to Controller and render our View templates.
    3. Step3: Add some code to CreateVm.js as,
      var urlPath = window.location.pathname;
      $(function () {
          ko.applyBindings(CreateVM);
      });

    var CreateVM = {
    Domiciles: ko.observableArray([Delhi’, Outside Delhi’]),
    Genders: ko.observableArray([Male’, Female’]),
    Students: ko.observableArray([]),
    StudentId: ko.observable(),
    FirstName: ko.observable(),
    LastName: ko.observable(),
    Age: ko.observable(),
    Batch: ko.observable(),
    Address: ko.observable(),
    Class: ko.observable(),
    School: ko.observable(),
    Domicile: ko.observable(),
    Gender: ko.observable(),
    SaveStudent: function () {
    $.ajax({
    url: /Student/Create’,
    type: post’,
    dataType: json’,
    data: ko.toJSON(this),
    contentType: application/json’,
    success: function (result) {
    },
    error: function (err) {
    if (err.responseText == Creation Failed”)
    { window.location.href = /Student/Index/’; }
    else {
    alert(Status:”+err.responseText);
    window.location.href = /Student/Index/’;;
    }
    },
    complete: function () {
    window.location.href = /Student/Index/’;
    }
    });
    }
    };

    On document load we apply bindings for CreateVM, then inside the view model method we initialize the observables to properties of Student, that will be bind to respective view.You can read more about observables in KO in first part of the series. There is a save function, that sends an ajax request to Student Controller’s Create method, and gets string result. data: ko.toJSON(this), means sending the object in JSON format to controller method.

    Student/Create Controller Method

    Modify the code of controller method of Create, to return JSON to the caller. The HTML templates bound with objects are actually bound to json properties, set in the methods of view model using Knockout Observables.
    The work on observer pattern, so that when model is updated the views automatically gets updated and when views get updated the models update itself, this is called two way binding.

    Controller Code

           [HttpPost]
    public string Create(Student student)
            {
    if (ModelState.IsValid)
                {
    if (!StudentExists(student))
                        db.Students.Add(student);
    else
    return Edit(student);
                    db.SaveChanges();
    return "Student Created";
                }
    return "Creation Failed";
            }

    View Code

    Change the code of the already created views to work with KO,
    For create.cshtml,

    <h2>Create</h2>
    <fieldset>
    <legend>Create Student</legend>

    <div class=”editor-label”>
    Student id
    </div>
    <div class=”editor-field”>
    <input data-bind=”value: StudentId” />
    </div>

    <div class=”editor-label”>
    First Name
    </div>
    <div class=”editor-field”>
    <input data-bind=”value: FirstName” />
    </div>

    <div class=”editor-label”>
    Last Name
    </div>
    <div class=”editor-field”>
    <input data-bind=”value: LastName” />
    </div>

    <div class=”editor-label”>
    Age
    </div>
    <div class=”editor-field”>
    <input data-bind=”value: Age” />
    </div>

    <div class=”editor-label”>
    Gender
    </div>
    <div class=”editor-field”>
    <select data-bind=”options: Genders, value: Gender, optionsCaption: ‘Select Gender…'”></select>
    </div>

    <div class=”editor-label”>
    Batch
    </div>
    <div class=”editor-field”>
    <input data-bind=”value: Batch” />
    </div>

    <div class=”editor-label”>
    Address
    </div>
    <div class=”editor-field”>
    <input data-bind=”value: Address” />
    </div>

    <div class=”editor-label”>
    Class
    </div>
    <div class=”editor-field”>
    <input data-bind=”value: Class” />
    </div>

    <div class=”editor-label”>
    School
    </div>
    <div class=”editor-field”>
    <input data-bind=”value: School” />
    </div>

    <div class=”editor-label”>
    Domicile
    </div>
    <div class=”item “>
    <select data-bind=”options: Domiciles, value: Domicile, optionsCaption: ‘Select Domicile…'”></select>
    </div>

    <p>
    <button type=”button” data-bind=”click: SaveStudent”>Save Student To Database</button>
    </p>
    </fieldset>
    <div>
    <a href=”@Url.Action(“Index”, “Student”)” >Back to List</a>
    </div>

    @section Scripts {
    @Scripts.Render(“~/Scripts/ViewModels/CreateVM.js”)
    }

    You can see I have used data-bind attribute of HTML5 to bind the View elements to View Models properties like data-bind="value: StudentId" , the same applies to all the editable elements. Click button is bound to SaveStudent method of view model.
    At the end of the page we have registered the CreateVM.js view model for this particular view by

    @section Scripts {
        @Scripts.Render("~/Scripts/ViewModels/CreateVM.js")
    }

    Tag.

  • Step3: We do the same set of operations for all the views, View models and Controller method, the code is as below,

For Edit

View Model

Code added in StudentListVM for Edit View Model, since it only perform get when it loads.

Controller methods

public ActionResult Edit(string id=null)
        {
            Student student = db.Students.Find(id);
if (student == null)
            {
return null;
            }
            JavaScriptSerializer serializer = new JavaScriptSerializer();
            ViewBag.InitialData = serializer.Serialize(student); 
return View();
        }

/// <summary>
/// Edits particular student details
/// </summary>
/// <param name=”student”></param>
/// <returns></returns>
[HttpPost]
public string Edit(Student student)
{
if (ModelState.IsValid)
{
db.Entry(student).State = EntityState.Modified;
db.SaveChanges();
return Student Edited”;
}
return Edit Failed”;
}

View

<h2>Edit</h2>
<fieldset>
<legend>Edit Student</legend>

<div class=”editor-label”>
Student id
</div>
<div class=”editor-field”>
<input data-bind=”value: StudentId” readonly=”readonly” />
</div>

<div class=”editor-label”>
First Name
</div>
<div class=”editor-field”>
<input data-bind=”value: FirstName” />
</div>

<div class=”editor-label”>
Last Name
</div>
<div class=”editor-field”>
<input data-bind=”value: LastName” />
</div>

<div class=”editor-label”>
Age
</div>
<div class=”editor-field”>
<input data-bind=”value: Age” />
</div>

<div class=”editor-label”>
Gender
</div>
<div class=”editor-field”>
<select data-bind=”options: Genders, value: Gender, optionsCaption: ‘Select Gender…'”></select>
</div>

<div class=”editor-label”>
Batch
</div>
<div class=”editor-field”>
<input data-bind=”value: Batch” />
</div>

<div class=”editor-label”>
Address
</div>
<div class=”editor-field”>
<input data-bind=”value: Address” />
</div>

<div class=”editor-label”>
Class
</div>
<div class=”editor-field”>
<input data-bind=”value: Class” />
</div>

<div class=”editor-label”>
School
</div>
<div class=”editor-field”>
<input data-bind=”value: School” />
</div>

<div class=”editor-label”>
Domicile
</div>
<div class=”editor-field”>
<select data-bind=”options: Domiciles, value: Domicile, optionsCaption: ‘Select Domicile…'”></select>
</div>
<p>
<button type=”button” data-bind=”click: SaveStudent”>Save Student To Database</button>
</p>
</fieldset>
<div>
<a href=”@Url.Action(“Index”, “Student”)”>Back to List</a>
</div>
@section Scripts {
<script>

$(function () {
ko.applyBindings(EditVM);
});

var initialData = @Html.Raw(ViewBag.InitialData)’; //get the raw json
var parsedJSON = $.parseJSON(initialData); //parse the json client side
var EditVM = {
Domiciles: ko.observableArray([Delhi’, ‘Outside Delhi’]),
Genders: ko.observableArray([Male’, ‘Female’]),
Students: ko.observableArray([]),
StudentId: ko.observable(parsedJSON.StudentId),
FirstName: ko.observable(parsedJSON.FirstName),
LastName: ko.observable(parsedJSON.LastName),
Age: ko.observable(parsedJSON.Age),
Batch: ko.observable(parsedJSON.Batch),
Address: ko.observable(parsedJSON.Address),
Class: ko.observable(parsedJSON.Class),
School: ko.observable(parsedJSON.School),
Domicile: ko.observable(parsedJSON.Domicile),
Gender: ko.observable(parsedJSON.Gender),
SaveStudent: function () {
$.ajax({
url: /Student/Edit’,
type: post’,
dataType: json’,
data: ko.toJSON(this),
contentType: application/json’,
success: function (result) {
},
error: function (err) {
if (err.responseText == Creation Failed”)
{ window.location.href = /Student/Index/’; }
else {
alert(Status:” + err.responseText);
window.location.href = /Student/Index/’;;
}
},
complete: function () {
window.location.href = /Student/Index/’;
}
});
}
};

</script>
}

For Delete

View Model

Code added in StudentListVM for Edit View Model, since it only perform get when it loads.

Controller methods

public ActionResult Delete(string id = null)
        {
            Student student = db.Students.Find(id);
if (student == null)
            {
return null;
            }
            JavaScriptSerializer serializer = new JavaScriptSerializer();
            ViewBag.InitialData = serializer.Serialize(student);
return View();
        }

/// <summary>
/// Delete particular student details
/// </summary>
/// <param name=”student”></param>
/// <returns></returns>
[HttpPost]
public string Delete(Student student)
{
Student studentDetail = db.Students.Find(student.StudentId);
db.Students.Remove(studentDetail);
db.SaveChanges();
return Student Deleted”;
}

View

@model KnockoutWithMVC4.Student

@{
ViewBag.Title = Delete”;
}

Delete Student

Are you sure you want to delete this?

Delete
<div class=display-label”>
Student Id

<div class=display-field”>
<input data-bind=value: StudentId” />

<div class=display-label”>
First Name

<div class=display-field”>
<input data-bind=value: FirstName” />

<div class=display-label”>
Last Name

<div class=display-field”>
<input data-bind=value: LastName” />

<div class=display-label”>
Age

<div class=display-field”>
<input data-bind=value: Age” />

<div class=display-label”>
Gender

<div class=display-field”>
<input data-bind=value: Gender” />

<div class=display-label”>
Batch

<div class=display-field”>
<input data-bind=value: Batch” />

<div class=display-label”>
Address

<div class=display-field”>
<input data-bind=value: Address” />

<div class=display-label”>
Class

<div class=display-field”>
<input data-bind=value: Class” />

<div class=display-label”>
School

<div class=display-field”>
<input data-bind=value: School” />

<div class=display-label”>
Domicile

<div class=display-field”>
<input data-bind=value: Domicile” />

<button type=button” data-bind=click: DeleteStudent”>Delete Student |
<a href=@Url.Action(“Index, “Student)”>Back to List

@section Scripts {

$(function () {
ko.applyBindings(DeleteVM);
});

var initialData = @Html.Raw(ViewBag.InitialData)’; //get the raw json
var parsedJSON = $.parseJSON(initialData); //parse the json client side
var DeleteVM = {
Domiciles: ko.observableArray([Delhi’, Outside Delhi’]),
Genders: ko.observableArray([Male’, Female’]),
Students: ko.observableArray([]),
StudentId: ko.observable(parsedJSON.StudentId),
FirstName: ko.observable(parsedJSON.FirstName),
LastName: ko.observable(parsedJSON.LastName),
Age: ko.observable(parsedJSON.Age),
Batch: ko.observable(parsedJSON.Batch),
Address: ko.observable(parsedJSON.Address),
Class: ko.observable(parsedJSON.Class),
School: ko.observable(parsedJSON.School),
Domicile: ko.observable(parsedJSON.Domicile),
Gender: ko.observable(parsedJSON.Gender),
DeleteStudent: function () {
$.ajax({
url: /Student/Delete’,
type: post’,
dataType: json’,
data: ko.toJSON(this),
contentType: application/json’,
success: function (result) {
},
error: function (err) {
if (err.responseText == Creation Failed”)
{ window.location.href = /Student/Index/’; }
else {
alert(Status:” + err.responseText);
window.location.href = /Student/Index/’;;
}
},
complete: function () {
window.location.href = /Student/Index/’;
}
});
}
};

}

For Index(To display list)

View Model

var urlPath = window.location.pathname;
$(function () {
    ko.applyBindings(StudentListVM);
    StudentListVM.getStudents();
});

//View Model
var StudentListVM = {
Students: ko.observableArray([]),
getStudents: function () {
var self = this;
$.ajax({
type: GET”,
url: /Student/FetchStudents’,
contentType: application/json; charset=utf-8″,
dataType: json”,
success: function (data) {
self.Students(data); //Put the response in ObservableArray
},
error: function (err) {
alert(err.status + : “ + err.statusText);
}
});
},
};

self.editStudent = function (student) {
window.location.href = /Student/Edit/’ + student.StudentId;
};
self.deleteStudent = function (student) {
window.location.href = /Student/Delete/’ + student.StudentId;
};

//Model
function Students(data) {
this.StudentId = ko.observable(data.StudentId);
this.FirstName = ko.observable(data.FirstName);
this.LastName = ko.observable(data.LastName);
this.Age = ko.observable(data.Age);
this.Gender = ko.observable(data.Gender);
this.Batch = ko.observable(data.Batch);
this.Address = ko.observable(data.Address);
this.Class = ko.observable(data.Class);
this.School = ko.observable(data.School);
this.Domicile = ko.observable(data.Domicile);
}

Controller methods

public JsonResult FetchStudents()
        {
            return Json(db.Students.ToList(), JsonRequestBehavior.AllowGet);
        }

View

@model IEnumerable

@{
ViewBag.Title = Index”;
}

Students List

<a href=@Url.Action(“Create, “Student)” >Create Student

 

First NameLast NameAgeGenderBatchAddressClassSchoolDomicile   <tbody data-bind=foreach: Students”>

<td data-bind=”text: StudentId”><td data-bind=text: FirstName”><td data-bind=text: LastName”><td data-bind=text: Age”><td data-bind=text: Gender”><td data-bind=text: Batch”><td data-bind=text: Address”><td data-bind=text: Class”><td data-bind=text: School”><td data-bind=text: Domicile”><a data-bind=click: editStudent”>Edit
<a data-bind=click: deleteStudent”>Delete

Student Id

@section Scripts {
@Scripts.Render(~/Scripts/ViewModels/StudentListVM.js”)
}

The return Json(db.Students.ToList(), JsonRequestBehavior.AllowGet); code returns the student object in json format, for binding to the view.
All set now, you can press F5 to run the application and we see, that application runs in the same manner as it executed before,

Now you can perform all the operations on this list.


Do not type anything else other than int for student id and Age, since validation checks are missing, they may cause error.

Now create new student ,


We see that the student is created successfully and added to the list,

In data base,


Similarly for Edit,

Change any field and press save.The change will be reflected in the list and data base,

For Delete,

Student Deleted.


And in database,

X) Knockout Attributes Glossary

. observable: Used to define model/entity properties. If these properties are bound with user interface and when value for these properties gets updated, automatically the UI elements bound with these properties will be updated with the new value instantaneously.
e.g. this.StudentId = ko.observable("1"); – => StudentId is the observable property. KO represent an object for the Knockout.js library.
The value of the observable is read as var id= this. StudentId ();

· observableArrayobservableArray represents a collection of data elements which required notifications. It’s used to bind with the List kind of elements.

e.g this.Students = ko.observableArray([]);
· applyBindings: This is used to activate knockout for the current HTML document or a specific UI element in HTML document. The parameter for this method is the view-model which is defined in JavaScript. This ViewModel contains the observable, observableArray and various methods.
Various other types of binding are used in this article:
. click: Represents a click event handler added to the UI element so that JavaScript function is called.
. value: This represents the value binding with the UI element’s value property to the property defined into the ViewModel.
The value binding should be used with  ,  , 
. visible: This is used to hide or unhide the UI element based upon the value passed to it’s binding.
. Text: This represent the text value of the parameter passed to the UI element.

XI) Conclusion

In this article of series Learning Knockout, we learned a lot of things about MVC, Entity Framework and Knockout.JS. We did practical hands on by creating a CRUD operations application too.

Therefore we can mark it as tasks done.
We’ll be covering more topics in my upcoming articles.
Note: few of the images in this article are taken via Google search.

Read more:

Other Series

My other series of articles:

For more technical articles you can reach out to CodeTeddy.
Happy Coding Smile | :) .

Introduction to Knockout.js and CRUD Operations in ASP.Net Web Forms Using Knockout.JS


Download Source Code

I) Introduction

The development paradigm has been changing rapidly for a last few years. The out of the box technologies have been introduced to develop applications with fast, scalable, extensible structure, easy to maintain and easy to use. Knockout.JS is also one of the examples of such emerging technologies. I take an opportunity to explain the concept and topic my way.
We’ll be discussing the technology from basic to advanced level by just following a road-map.

II) Our Road-map


We’ll learn Knockout.JS in the following three parts:
  1. Part 1: Introduction to Knockout.js and CRUD Operations in ASP.NET Web Forms using Knockout.JS and Entity Framework.
  2. Part 2: Complete end to end CRUD operations using Knockout.JS and Entity Framework in MVC4 application.

III) Part 1: Introduction to Knockout.js and CRUD Operations in ASP.NET Web Forms using Knockout.JS

We’ll discuss this part by starting with an introduction to knockout, MVVM and observer pattern. Then by setting up a basic environment in knockout.js, thereby creating an ASP.NET web forms application and performing CRUD operations.

IV) Knockout

In today’s changing trend of development, data driven apps depend largely on JavaScript and JS based libraries such as jQuery. The client side programming appears to become more and more complex because the user interface becomes richer. In scenarios like this, the data binding and dependency tracking are highly desirable in the applications for further extensibility of the application. Knockout JS fulfills these rich requirements on client side programming and makes a developers’ life easy and joyful. Let’s discuss KO in detail.

Knockout.JS (KO) is basically a JS library that enables Declarative Bindings using an ‘Observable’ ViewModel on the client (browser) following observer pattern approach, enabling UI to bind and refresh itself automatically whenever the data bound is modified. Knockout.JS provides its own templating pattern that helps us to bind our view model data easily. KO works on MVVM pattern i.e. Model-View-ViewModel.
As the architecture is shown, Views interact with View Models in a two way binding manner, i.e., when model is changed, view updates itself and when view is updated, model too updates itself instantaneously.
KO provides 3 most important features like:
  • Automatic Refresh of UI
  • Two way binding
  • Templating
The whole idea of KO derives from these three major functionalities. KO also helps in developing single page applications (SPAs). SPAs are out of the box new way of developing rich internet applications (RIAs) in today’s era.

V) Model-View-View Model (MVVM)

When we develop a rich UI internet based application, we create Views (UI like HTML and aspx pages) using server controls, HTML controls and then extend our application by writing business logic behind those views like event handling, property binding, creating entities. This approach increases complexities when the application is too large. Here, we require separation of concerns and maintainability of the application, especially on client side.
The MVVM pattern includes three key parts:
  1. Model (Business rule, data access, model classes, Data displayed in UI)
  2. View (User interface (html, aspx, cshtml…))
  3. ViewModel (Event handling, binding, business logic)
Model refers to our application data and domain model, i.e., entities. In a traditional ASP.NET web application, the data is basically stored inside database or files and UI fetches the data using client-server request like Ajax or direct bind itself.
View Model contains the User Interface level operations/methods/functions, performed on model data to bind the outcome to view. The operations include business logic validations and checks to be performed before binding data to UI. View models act as interface between model and views and act as a wrapper over model prior binding to Views.
View is the user interface of our application. View talks to View Model to invoke certain methods/operations as explained above. View gets updated automatically whenever data from the View Model changes.
MVVM provides a clear separation of concerns between the user interface (UI) and the business logic.
In the MVC pattern, a view acts as the broker agent between the Model (the data displayed in the View) and the Controller (server-side endpoint that takes data from the View and performs some action on that data and provides a response.

VI) Observables for Two Way Binding

KO provides Observables in the library to be bound to UI elements and simultaneously code is written to view models, so that when view updates the data the model updates itself and vice versa, for example, in the following code:
<tr>
    <td>Batch :</td>
    <td>
        <input data-bind="value: Batch" /></td>
    <td><span data-bind="text: Batch" /></td>
</tr>
<tr>
    <td>Address :</td>
    <td>
        <input data-bind="value: Address" /></td>
    <td><span data-bind="text: Address" /></td>
</tr>
<tr>
    <td>Class :</td>
    <td>
        <input data-bind="value: Class" /></td>
    <td><span data-bind="text: Class" /></td>
</tr>
The above code shows a part of view, you can see the elements are bound to properties like text and value, these properties are provided by KO, and the right side of these properties are property key names which are bind in view-models with the help of observables like shown below:
    var self = this;
    self.Batch = ko.observable();
    self.Address = ko.observable();
    self.Class = ko.observable();
So this would be the code in View model, anyways we’ll be discussing all this in detail.
NOTE: Data-bind is an HTML5 attribute.

VII) Setting up Environment in Visual Studio for KO

We go step by step to set up Knockout js environment in Visual Studio.
The pre-requisite is Visual Studio must be version greater than or equal to 12. I am using Visual Studio 2013 Express.
Step 1: Open Visual Studio and create a simple ASP.NET application, I have given it a name KOSetup.
 
Step 2: Right click on project, and in context menu select manage Nuget packages to install JQuery and KO.
 
Step 3: Type jQuery in search text box to get the latest compatible jQuery library. Click install to install the library.
 
Step 4: In the similar fashion, search ‘knockout’ in search textbox and install knockoutjs library in your application.
 
Step 5: Our solution will look like we have a folder created named Scripts and that contains jQuery and knockout libraries.
 
Step 6: Now right click the project and add an aspx page, I named that page LearnKO.aspx.
 
Step 7: Similarly create a JavaScript file and add that to the project , I named that file as LearnKO.js.
 
Step 8: Open the learnKO.js file and drag the jQuery file and knockout.js library file to the LearKO.js file, we see in the below picture that reference of both the files is created on the js file. We did this because it will prove us intellisense support for jQuery and knockout on our LearnKO.js file.
 
Step 9: Write document.ready function of jquery in our LearnKO.js file. Document.ready function is fired when our HTML document object model is loaded in browser.
This is all we have to do to setup knockout, now we know how to setup initial environment to use knockout.js in our application.
We proceed now to create the application, talk to database and create template and view model.

VIII) Creating Knockout Application

Step 10: For communication to database, add Entity Framework library in the same manner as we added JQuery and KO, installing Entity Framework library will add the EF DLL to the project. We’ll talk to database using Entity Framework of Microsoft. Alternatively, there are a number of ways to talk to database like ADO.NET, LINQ to SQL, etc. But first things first, create a database you have to use in SQL Server. I’ve provided the script for the same.
Step 11: Right click project and add ADO.NET Entity data Model, click Add, and follow these below steps:
Step 12: Following is step two of Entity Data Model. You can choose model contents from database you already created. So select “Generate From database” option. Click Next.
Step 13: Choose the table you want to add, i.e., Student table as shown below in the figure. Name the model asLearningKOModel. Click Finish.
Step 14: We get certain files in our solution like context and tt files. We also get Student.CS file, that will act as our server side domain model. The context class contains the data communication methods of Entity Framework.
Step 15: Write three methods with the help of Entity Framework in our aspx.cs page. One method to fetch all theStudents and another method to save and delete a student to/from database, as shown below. Mark them as web method so that they could be called from client side.
The code is as follows:
#region Public Web Methods.
        /// <summary>
        /// Gets Student Details
        /// </summary>
        /// <returns></returns>
        [WebMethod]
        public static Student[] FetchStudents()
        {
            LearningKOEntities dbEntities = new LearningKOEntities();
            var data = (from item in dbEntities.Students
                        orderby item.StudentId
                        select item).Take(5);
            return data.ToArray();
        }

/// <summary>
/// Saves Student Details
/// </summary>
/// <param name=”data”></param>
/// <returns></returns>
[WebMethod]
public static string SaveStudent(Student[] data)
{
try
{
var dbContext = new LearningKOEntities();
var studentList = from dbStududent in dbContext.Students select dbStududent;
foreach (Student userDetails in data)
{
var student = new Student();
if (userDetails != null)
{
student.StudentId = userDetails.StudentId;
student.FirstName = userDetails.FirstName;
student.LastName = userDetails.LastName;
student.Address = userDetails.Address;
student.Age = userDetails.Age;
student.Gender = userDetails.Gender;
student.Batch = userDetails.Batch;
student.Class = userDetails.Class;
student.School = userDetails.School;
student.Domicile = userDetails.Domicile;
}
Student stud=(from st in studentList where
st.StudentId==student.StudentId select st).FirstOrDefault();
if (stud == null)
dbContext.Students.Add(student);
dbContext.SaveChanges();
}
return Data saved to database!”;
}
catch (Exception ex)
{
return Error: “ + ex.Message;
}
}

/// <summary>
/// Deletes Student Details
/// </summary>
/// <param name=”data”></param>
/// <returns></returns>
[WebMethod]
public static string DeleteStudent(Student data)
{
try
{
var dbContext = new LearningKOEntities();
var student = dbContext.Students.FirstOrDefault
(userId => userId.StudentId == data.StudentId);
if (student != null)
{
if (student != null)
{
dbContext.Students.Remove(student);
dbContext.SaveChanges();
}
}
return Data deleted from database!”;

}
catch (Exception ex)
{
return Error: “ + ex.Message;
}
}
#endregion

 
Step 16: Open the aspx page we created and add the following code to it. The code provides templates in HTML bound to model properties, one to add Student and other displaying Student List.
<table style="width:100%;" >
            <tbody>
                <tr>
                    <th style="width:100px;">Property Name</th>
                    <th style="width:100px;">Enter Value</th>
                    <th style="width:100px;">Example of two Way Binding</th>
                </tr>
                </tbody>
            <tr>
                <td>Student ID (int):</td>
                <td>
                    <input data-bind="value: StudentId" />
                    </td> <!--,valueUpdate:'keypress'-->
                <td><span data-bind="text: StudentId" /></td>
            </tr>
            <tr>
                <td>First Name :</td>
                <td>
                    <input data-bind="value: FirstName" /></td>
                <td  ><span data-bind="text: FirstName" /></td>
            </tr>
            <tr>
                <td>Last Name :</td>
                <td>
                    <input data-bind="value: LastName" /></td>
                <td><span data-bind="text: LastName" /></td>
            </tr>

<tr>
<td>Student Age (int) :</td>
<td>
<input data-bind=”value: Age” /></td>
<td><span data-bind=”text: Age” /></td>
</tr>
<tr>
<td>Gender :</td>
<td>
<select data-bind=”options: Genders, value:
Gender, optionsCaption: ‘Select Gender…'”
></select></td>
<td><span data-bind=”text: Gender” /></td>
</tr>
<tr>
<td>Batch :</td>
<td>
<input data-bind=”value: Batch” /></td>
<td><span data-bind=”text: Batch” /></td>
</tr>
<tr>
<td>Address :</td>
<td>
<input data-bind=”value: Address” /></td>
<td><span data-bind=”text: Address” /></td>
</tr>
<tr>
<td>Class :</td>
<td>
<input data-bind=”value: Class” /></td>
<td><span data-bind=”text: Class” /></td>
</tr>
<tr>
<td>School :</td>
<td>
<input data-bind=”value: School” /></td>
<td><span data-bind=”text: School” /></td>
</tr>
<tr>
<td>Domicile :</td>
<td>
<select data-bind=”options: Domiciles, value:
Domicile, optionsCaption: ‘Select Domicile…'”
></select>
</td>
<td><span data-bind=”text: Domicile” /></td>
</tr>
<tr>
<td colspan=”3″>
<button type=”button” data-bind=”click:
AddStudent”
>Add Student</button>
<button type=”button” data-bind=”click:
SaveStudent”
>Save Student To Database</button>
</td>
</tr>

</table>
</div>

<div style=”width:70%;float:left;display:inline-block;”>
<h2>List of Students</h2>
<table style=”width:100%;” data-bind=”visible:
Students().length > 0″
border=”0″>
<tr>
<th>Student Id</th>
<th>First Name</th>
<th>Last Name</th>
<th>Age</th>
<th>Gender</th>
<th>Batch</th>
<th>Address</th>
<th>Class</th>
<th>School</th>
<th>Domicile</th>
</tr>
<tbody data-bind=”foreach: Students”>
<tr>
<td><span data-bind=”text: StudentId” /></td>
<td>
<input data-bind=”value: FirstName” /></td>
<td>
<input data-bind=”value: LastName” /></td>
<td>
<input data-bind=”value: Age” /></td>

<td>
<select data-bind=”options: $root.Genders,
value: Gender”
></select></td>
<td>
<input data-bind=”value: Batch” /></td>
<td>
<input data-bind=”value: Address” /></td>
<td>
<input data-bind=”value: Class” /></td>
<td>
<input data-bind=”value: School” /></td>
<td>
<select data-bind=”options: $root.Domiciles,
value: Domicile”
></select></td>

<td><a href=”#” data-bind=”click: $root.
DeleteStudent”
>Delete</a></td>
</tr>
</tbody>
</table>

There are two HTML tables, one for adding student to database and other showing all the students having delete anchor link to delete the student, these template properties will be bound in view model, where we write method to communicate with data base and call Web Methods we created in aspx.cs page. The Viewmodel also contains observables to be bound to these properties.
Step 17: Now it’s time to create ViewModel, Open the learnKO.js file and add codes to fetch, save and delete student, and observables bound to properties binded on controls of HTML page.
/// <reference path="jquery-2.0.3.min.js" />
/// <reference path="knockout-3.0.0.js" />

function Student(data) {
    this.StudentId = ko.observable(data.StudentId);
    this.FirstName = ko.observable(data.FirstName);
    this.LastName = ko.observable(data.LastName);
    this.Age = ko.observable(data.Age);
    this.Gender = ko.observable(data.Gender);
    this.Batch = ko.observable(data.Batch);
    this.Address = ko.observable(data.Address);
    this.Class = ko.observable(data.Class);
    this.School = ko.observable(data.School);
    this.Domicile = ko.observable(data.Domicile);
}

function StudentViewModel() {
var self = this;
self.Domiciles = ko.observableArray([Delhi’, Outside Delhi’]);
self.Genders = ko.observableArray([Male’, Female’]);
self.Students = ko.observableArray([]);
self.StudentId = ko.observable();
self.FirstName = ko.observable();
self.LastName = ko.observable();
self.Age = ko.observable();
self.Batch = ko.observable();
self.Address = ko.observable();
self.Class = ko.observable();
self.School = ko.observable();
self.Domicile = ko.observable();
self.Gender = ko.observable();

self.AddStudent = function () {
self.Students.push(new Student({
StudentId: self.StudentId(),
FirstName: self.FirstName(),
LastName: self.LastName(),
Domicile: self.Domicile(),
Age: self.Age(),
Batch: self.Batch(),
Address: self.Address(),
Class: self.Class(),
School: self.School(),
Gender: self.Gender()
}));
self.StudentId(),
self.FirstName(),
self.LastName(),
self.Domicile(),
self.Age(),
self.Batch(),
self.Address(),
self.Class(),
self.School(),
self.Gender()
};

self.DeleteStudent = function (student) {

$.ajax({
type: POST”,
url: LearnKO.aspx/DeleteStudent’,
data: ko.toJSON({ data: student }),
contentType: application/json; charset=utf-8″,
success: function (result) {
alert(result.d);
self.Students.remove(student)
},
error: function (err) {
alert(err.status + – “ + err.statusText);
}
});
};

self.SaveStudent = function () {
$.ajax({
type: POST”,
url: LearnKO.aspx/SaveStudent’,
data: ko.toJSON({ data: self.Students }),
contentType: application/json; charset=utf-8″,
success: function (result) {
alert(result.d);
},
error: function (err) {
alert(err.status + – “ + err.statusText);
}
});
};

$.ajax({
type: POST”,
url: LearnKO.aspx/FetchStudents’,
contentType: application/json; charset=utf-8″,
dataType: json”,
success: function (results) {
var students = $.map(results.d, function (item) {
return new Student(item)
});
self.Students(students);
},
error: function (err) {
alert(err.status + – “ + err.statusText);
}
})
}

$(document).ready(function () {
ko.applyBindings(new StudentViewModel());
});

We create StudentViewModel() as our primary view model JavaScript function, that contains all the business logic and operations.
We bind this View model on document ready function by the KO method named applyBindings. This initializes our view model, ko.applyBindings(new StudentViewModel());
Function function Student(data) contains observables bound to model properties.
We can create observable arrays of Domiciles and genders to bind to the dropdown list of our HTML. Ko provides these observables and other such properties to bind to model.
  • observable: Used to define model/entity properties. If these properties are bound with user interface and when value for these properties gets updated, automatically the UI elements bound with these properties will be updated with the new value instantaneously.

E.g. this.StudentId = ko.observable(“1”); - => StudentId is the observable property. KO represent an object for the Knockout.js library.

The value of the observable is read as var id= this. StudentId ();

  • observableArrayobservableArray represents a collection of data elements which required notifications. It’s used to bind with the List kind of elements.
    E.g. this.Students = ko.observableArray([]);
  • applyBindings: This is used to activate knockout for the current HTML document or a specific UI element in HTML document. The parameter for this method is the view-model which is defined in JavaScript. ThisViewModel contains the observableobservableArray and various methods.

 

Various other types of binding are used in this article:
  • click: Represents a click event handler added to the UI element so that JavaScript function is called.
  • value: This represents the value binding with the UI element’s value property to the property defined into theViewModel.
The value binding should be used with :
  • visible: This is used to hide or unhide the UI element based upon the value passed to its binding.
  • Text: This represents the text value of the parameter passed to the UI element.
Step 18: Include js files and stylesheet (you can create your own stylesheet file) to head section of aspx page.
 
Step 19: Press F5 to run the application, and we’ll be shown a page having HTML controls as follows:
List of Students shows the list of students from database, bound to viewmodel’s event.
Try to create a new student and add student, then save it to database, it will automatically be added to the right hand side list.
We can see that Domicile and Genders drop down lists are bound to our Viewmodel’s properties.
Note: Do not give string in StudentId and Age as no validation is put on those fields, code may break.
Create Student:
Student added to list and database:
Job done!
Now you can say that you have become a knockout.js developer.

IX) Conclusion

We learnt a lot in this article about how to set up knockout.js in Visual Studio, lots of theory and also created a sample application just to hands-on the concept. There are numerous articles and blogs related to the same concept, you can explore more and more to learn. In the next article, I’ll explain creating a sample application and performing CRUD operations in MVC4 with knockout js and Entity Framework. Now pat your back to have done a great job by learning a new concept.
Note: Few of the images in this article are taken via Google search.

Complete CRUD Operations in MVC 4 using Entity Framework 5 Without Writing a Single Line of Code


Introduction

In this article, I’ll describe how to perform basic CRUD operations in an MVC4 application with the help of Entity Framework 5 without writing a single line of code. EF and MVC had advanced themselves to the level that we don’t have to put effort in doing extra work.

I) MVC

Model: The business entity on which the overall application operates. Many applications use a persistent storage mechanism (such as a database) to store data. MVC does not specifically mention the data access layer because it is understood to be encapsulated by the Model.
View: The user interface that renders the model into a form of interaction.
Controller: Handles a request from a view and updates the model that results a change in Model’s state.
To implement MVC in .NET, we need mainly three classes (ViewController and the Model).

II) Entity Framework

Let’s have a look at the standard definition of Entity Framework given by Microsoft:

“The Microsoft ADO.NET Entity Framework is an Object/Relational Mapping (ORM) framework that enables developers to work with relational data as domain-specific objects, eliminating the need for most of the data access plumbing code that developers usually need to write. Using the Entity Framework, developers issue queries using LINQ, then retrieve and manipulate data as strongly typed objects. The Entity Framework’s ORM implementation provides services like change tracking, identity resolution, lazy loading, and query translation so that developers can focus on their application-specific business logic rather than the data access fundamentals.”

In a simple language, Entity framework is an Object/Relational Mapping (ORM) framework. It is an enhancement to ADO.NET, an upper layer to ADO.NET that gives developers an automated mechanism for accessing & storing the data in the database.
Hope this gives a glimpse of an ORM and EntityFramework.

III) MVC Application

Step 1: Create a database named LearningKO and add a table named student to it, script of the table is as follows:
USE [LearningKO]
GO
/****** Object: Table [dbo].[Student] Script Date: 12/04/2013 23:58:12 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Student](
[StudentId] [nvarchar](10) NOT NULL,
[FirstName] [nvarchar](50) NULL,
[LastName] [nvarchar](50) NULL,
[Age] [int] NULL,
[Gender] [nvarchar](50) NULL,
[Batch] [nvarchar](50) NULL,
[Address] [nvarchar](50) NULL,
[Class] [nvarchar](50) NULL,
[School] [nvarchar](50) NULL,
[Domicile] [nvarchar](50) NULL,
CONSTRAINT [PK_Student] PRIMARY KEY CLUSTERED
(
[StudentId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, _
IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
INSERT [dbo].[Student] ([StudentId], [FirstName], [LastName], [Age], _
[Gender], [Batch], [Address], [Class], [School], [Domicile]) _
VALUES (N'1', N'Akhil', N'Mittal', 28, N'Male', N'2006', N'Noida', N'Tenth', N'LFS', N'Delhi')
INSERT [dbo].[Student] ([StudentId], [FirstName], [LastName], [Age], _
[Gender], [Batch], [Address], [Class], [School], [Domicile]) _
VALUES (N'2', N'Parveen', N'Arora', 25, N'Male', N'2007', N'Noida', N'8th', N'DPS', N'Delhi')
INSERT [dbo].[Student] ([StudentId], [FirstName], [LastName], [Age], _
[Gender], [Batch], [Address], [Class], [School], [Domicile]) _
VALUES (N'3', N'Neeraj', N'Kumar', 38, N'Male', _
N'2011', N'Noida', N'10th', N'MIT', N'Outside Delhi')
INSERT [dbo].[Student] ([StudentId], [FirstName], [LastName], [Age], _
[Gender], [Batch], [Address], [Class], [School], [Domicile]) _
VALUES (N'4', N'Ekta', N'Mittal', 25, N'Female', N'2005', N' Noida', N'12th', N'LFS', N'Delhi')

Step 2: Open your Visual Studio (Visual Studio Version should be greater than or equal to 12) and add an MVC Internet application.
I have given it a name “KnockoutWithMVC4”.
Step 3: You’ll get a full structured MVC application with default Home controller in the Controller folder. By default, entity framework is downloaded as a package inside application folder but if not, you can add entity framework package by right clicking the project, select manage nugget packages and search and install Entity Framework.
Step 4: Right click project file, select add new item and add ADO.NET entity data model, follow the steps in the wizard as shown below:
Generate model from database, select your server and LearningKO database name, the connection string will automatically be added to your Web.Config, name that connection string as LearningKOEntities.
Select tables to be added to the model. In our case, it’s Student Table.

Step 5: Now add a new controller to the Controller folder, right click controller folder and add a controller namedStudent. Since we have already created our Datamodel, we can choose for an option where CRUD actions are created by chosen Entity Framework Datamodel:
  • Name your controller as StudentController.
  • From Scaffolding Options, select “MVC controller with read/write actions and views, using Entity Framework”.
  • Select Model class as Student, that lies in our solution.
  • Select Data context class as LearningKOEntities that is added to our solution when we added EF data model.
  • Select Razor as rendering engine for views.
  • Click Advanced options, select Layout or master page and select _Layout.cshtml from the shared folder.

Step 6: We see our student controller prepared with all the CRUD operation actions as shown below:
using System;
using System.Collections.Generic;
using System.Data;
using System.Data.Entity;
using System.Linq;
using System.Web;
using System.Web.Mvc;

namespace KnockoutWithMVC4.Controllers
{
public class StudentController : Controller
{
private LearningKOEntities db = new LearningKOEntities();

//
// GET: /Student/

public ActionResult Index()
{
return View(db.Students.ToList());
}

//
// GET: /Student/Details/5

public ActionResult Details(string id = null)
{
Student student = db.Students.Find(id);
if (student == null)
{
return HttpNotFound();
}
return View(student);
}

//
// GET: /Student/Create

public ActionResult Create()
{
return View();
}

//
// POST: /Student/Create

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create(Student student)
{
if (ModelState.IsValid)
{
db.Students.Add(student);
db.SaveChanges();
return RedirectToAction("Index");
}

return View(student);
}

//
// GET: /Student/Edit/5

public ActionResult Edit(string id = null)
{
Student student = db.Students.Find(id);
if (student == null)
{
return HttpNotFound();
}
return View(student);
}

//
// POST: /Student/Edit/5

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Edit(Student student)
{
if (ModelState.IsValid)
{
db.Entry(student).State = EntityState.Modified;
db.SaveChanges();
return RedirectToAction("Index");
}
return View(student);
}

//
// GET: /Student/Delete/5

public ActionResult Delete(string id = null)
{
Student student = db.Students.Find(id);
if (student == null)
{
return HttpNotFound();
}
return View(student);
}

//
// POST: /Student/Delete/5

[HttpPost, ActionName("Delete")]
[ValidateAntiForgeryToken]
public ActionResult DeleteConfirmed(string id)
{
Student student = db.Students.Find(id);
db.Students.Remove(student);
db.SaveChanges();
return RedirectToAction("Index");
}

protected override void Dispose(bool disposing)
{
db.Dispose();
base.Dispose(disposing);
}
}
}

Step 7: Open App_Start folder and, change the name of controller from Home to Student.
The code will become as:
public static void RegisterRoutes(RouteCollection routes)
{
routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

routes.MapRoute(
name: "Default",
url: "{controller}/{action}/{id}",
defaults: new { controller = "Student",
action = "Index", id = UrlParameter.Optional }
);
}

Step 8: Now press F5 to run the application, and you’ll see the list of all students we added into table Student while creating it is displayed. Since the CRUD operations are automatically written, we have action results for display list and other Edit, Delete and Create operations. Note that views for all the operations are created in Views Folder underStudent Folder name.
Now you can perform all the operations on this list.
Since I have not provided any validation checks on model or creating an existing student id, the code may break, so I am calling Edit Action in create when we find that id already exists.
Now create new student.
We see that the student is created successfully and added to the list.
In database:
Similarly for Edit:
Change any field and press save. The change will be reflected in the list and database:
For Delete:
Student deleted.
And in database:
Not a single line of code is written till now.

Conclusion

In this tutorial, we learnt to setup environment for MVC and Entity Framework 5 and perform CRUD operations on Student model without writing a single line of code. You can expand the application by adding multiple Controllers, Models and Views.
Note: Few of the images in this article are taken via Google search.
You can follow my articles at csharppulse.blogspot.in.
Happy coding!

LINQ Interview Questions (All in One)


I. Introduction

This article explains some of the main and important concepts of LINQ and C#. The article explains LINQ in detail, and covers almost every concept of LINQ and C# 2.0 and 3.0. This is an effort to put together the important concepts in one place to make it easy to follow. I will explain the topics by giving simple examples, rather than explaining too much theory behind the examples.

II. Pre-requisites

  • The reader of this article should be aware of the LINQ term.
  • The reader should have basic knowledge of SQL.
  • The reader should know how to code in C#.

III. Overview

LINQ is so dynamic that it could be described in several ways as:
  • LINQ is a uniform programming model for any kind of data. LINQ enables you to query and manipulate data with a consistent model that is independent from data sources.
  • LINQ is just another tool for embedding SQL queries into code.
  • LINQ is yet another data abstraction layer.

IV. What Is LINQ?

In my terms, LINQ is actually a methodology that simplifies and unifies the implementation of any kind of data access. LINQ does not force you to use a specific architecture; it facilitates the implementation of several existing architectures for accessing data.
LINQ is a programming model that introduces queries as a first-class concept into any Microsoft .NET language. However, complete support for LINQ requires some extensions in the language used.
These extensions boost productivity, thereby providing a shorter, meaningful, and expressive syntax to manipulate data.
Examining a simple LINQ query:
var query = from c in Customers
                     where c.Country == "Italy"
                     select c.CompanyName;
The SQL-like syntax used in LINQ is called a query expression, but remember LINQ is not the same as embedded SQL.

V. How LINQ Works Internally

When we look at the following query expression:
Customer[] Customers = GetCustomers();
var query = from c in Customers where c.Country == "Italy“ select c;
When the compiler compiles the above code, it generates the following code:
Customer[] Customers = GetCustomers();
IEnumerable query =
Customers .Where( c => c.Country == "Italy" );
Look at another query expression:
var query = from c in Customers
where c.Country == "Italy“ orderby c.Name
select new { c.Name, c.City };
and the code when compiled:
var query = Customers.Where( c => c.Country == "Italy" ).OrderBy( c => c.Name ).Select
( c => new { c.Name, c.City } );
Therefore, we see the compiler internally treats this SQL type query as a simple C# lambda expressions query.
One important thing about LINQ to keep in mind is that a LINQ query is not really executed until there is access to the query result, this is also called on demand loading or lazy loading,
Example:
1. var query = from c in Customers ...
      foreach ( string name in query ) ...

2. var query = from c in Customers …
List customers = query.ToList();

In both the above mentioned examples, the LINQ query does not execute in the first line actually, it is executed in the second line when that query variable is actually addressed or used. Write a code and try it yourself.

VI. Relational Model vs. Hierarchical/Graph Model

LINQ works on relational and hierarchical model. Rather than explaining theory, I would explain the concept with these examples:
  • In a relational model:
    var query = from c in Customers join o in Orders on c.CustomerID equals o.CustomerID
    select new {  c.CustomerID, c.CompanyName, o.OrderID };
  • In a hierarchical model:
    var query = from c in Customers from o in c.Orders
    select new {  c.Name, o.Quantity, o.Product. ProductName  };
The above two statements clearly state both the models, if you are aware of SQL queries, you can get the above given examples.
Follow the below mentioned scenarios.

A. Type declarations with simple relationships

class Customer
{
 public string Name;
 public string City;

public Order[] Orders;
}

public class Order
{
public int Quantity;
public Product Product;
}

public class Product
{
public int ProductId;
public decimal Price;
public string ProductName;
}

B. Type declarations with two-way relationships

public class Customer
{
public string Name;
public string City;
public Order[] Orders;
}

public class Order
{
public int Quantity;
public Product Product;
public Customer Customer;
}

public class Product
{
public int ProductId;
public decimal Price;
public string ProductName;
public Order[] Orders;
}

C. Querying the graph of objects

var query = from p in products where p.ProductId == 3 from o in p.Orders
select o;
  • If you have entity relationships in your data model, you can still use explicit relationships in a LINQ:
    var query = from c in Customers join s in Suppliers on c.City equals s.City
    select new { c.City, c.Name, SupplierName = s.Name };

    And something like the following will be returned:

    City=Torino Name=Marco SupplierName=Trucker
    City=Dallas Name=James SupplierName=FastDelivery
    City=Dallas Name=James SupplierName=Horizon
    City=Seattle Name=Frank SupplierName=WayFaster
  • LINQ can return a hierarchy or graph of objects for a SQL query that contains several entities with one or more one-to-many relationships:
    var query = from c in Customers join s in _
    Suppliers on c.City equals s.City into customerSuppliers
    select new { c.City, c.Name, customerSuppliers };

Here is how the hierarchized results might appear:

City=Torino Name=Marco customerSuppliers=...
customerSuppliers: Name=Trucker City=Torino
City=Dallas Name=James customerSuppliers=...
customerSuppliers: Name=FastDelivery City=Dallas
customerSuppliers: Name=Horizon City=Dallas
City=Seattle Name=Frank customerSuppliers=...
customerSuppliers: Name=WayFaster City=Seattle
  • LINQ requires to describe your data in terms of entities that are also types in the language.
  • A LINQ query, it is always a set of operations on instances of some classes.
  • These objects might be the real container of data, or they might be a simple description (in terms of metadata) of the external entity one is going to manipulate.
  • A query can be sent to a database through an SQL command only if it is applied to a set of types that map tables and relationships contained in the database.
  • The conversion of all these operations in SQL commands is the responsibility of the LINQ engine.
  • Class declaration mapped on a database table:
[Table("Products")]
public class Product
{

[Column(IsPrimaryKey=true)]
public int IdProduct;
[Column(Name=UnitPrice”)]
public decimal Price;
[Column()]
public string ProductName;

[Column()]
public bool Taxable;
[Column()]
public decimal Tax;
}

D. Database update calling the SubmitChanges() method

Example:
var taxableProducts = from p in db.Products where p.Taxable == true select p;

foreach( Product product in taxableProducts ) { RecalculateTaxes( product ); }
db.SubmitChanges();

VII. XML Manipulation

LINQ has a different set of classes and extensions to support the manipulation of XML data.
e.g. A fragment of an XML file of orders:
<?xml version="1.0" encoding="utf-8" ?>
<orders xmlns="http://schemas.devleap.com/Orders">
<order idCustomer="ALFKI" idProduct="1" quantity="10" price="20.59"/>
<order idCustomer="ANATR" idProduct="5" quantity="20" price="12.99"/>
<order idCustomer="KOENE" idProduct="7" quantity="15" price="35.50"/>
 </orders>

A. Reading the XML file of orders using an XmlReader

String nsUri = "http://schemas.devleap.com/Orders";
XmlReader xmlOrders = XmlReader.Create( "Orders.xml" );
List orders = new List();

Order order = null;

while (xmlOrders.Read())
{

switch (xmlOrders.NodeType)
{
case XmlNodeType.Element:

if ((xmlOrders.Name == order”) && (xmlOrders.NamespaceURI == nsUri))
{

order = new Order();
order.CustomerID = xmlOrders.GetAttribute( idCustomer” );

order.Product = new Product();
order.Product.IdProduct = Int32.Parse
( xmlOrders.GetAttribute( idProduct” ) );
order.Product.Price = Decimal.Parse
( xmlOrders.GetAttribute( price” ) );
order.Quantity = Int32.Parse
( xmlOrders.GetAttribute( quantity” ) );
orders.Add( order );
}
break;
}
}

B. An XQuery like the following one to select nodes

for $order in document("Orders.xml")/orders/order return $order

C. Reading the XML file using LINQ to XML

XDocument xmlOrders = XDocument.Load( "Orders.xml" );
XNamespace ns = "http://schemas.devleap.com/Orders";
var orders = from o in xmlOrders.Root.Elements( ns + "order" )
select new Order {
CustomerID = (String)o.Attribute( "idCustomer" ),
Product = new Product {
IdProduct = (Int32)o.Attribute("idProduct"), Price = (Decimal)o.Attribute("price")
},
Quantity = (Int32)o.Attribute("quantity")
};

VIII. Language Integration

Language integration is a fundamental aspect of LINQ. It allows you to write code such as the following:
var query =
from c in Customers
where c.Country == "Italy" orderby c.Name
select new { c.Name, c.City };
Instead of writing this code:
var query = Customers
.Where( c => c.Country == "Italy" )
.OrderBy( c => c.Name )
.Select( c => new { c.Name, c.City } );
  • LINQ enables a more declarative style of coding for C# and Visual Basic.
  • In SQL, we describe what you want. In C#, we describe how to obtain the expected result.
  • Declarative programming can take advantage of services offered by compilers and frameworks, and in general, it is easier to read and maintain.
  • This single “feature” can be the most important one because it boosts programmers’ productivity.

IX. Type Checking

Another important aspect of language integration is type checking. Whenever data is manipulated by LINQ, no unsafe cast is necessary. Data is always strongly typed, including both the queried collections and the single entities that are read and returned.
This enables the use of Visual Studio features such as IntelliSense and Refactoring, even with LINQ queries.

X. Transparency Across Different Type Systems

The type system of the Microsoft .NET Framework and the type system of SQL Server are different. Using LINQ, we give precedence to the .NET type system because it is the one supported by any language that hosts a LINQ query. It is necessary to convert many types of data between these two worlds. LINQ handles this conversion for you automatically, making the differences in type systems almost completely transparent to the programmer.

XI. LINQ Flavors

LINQ is a technology that covers many data domains. Some of these domains are included in those “LINQ Flavors” that Microsoft provides as part of the .NET 3.5 Framework, as shown below:

XII. LINQ to Objects

LINQ to Objects has the goal of manipulating collections of objects, which can be related to each other to form a hierarchy or a graph. From a certain point of view, LINQ to Objects is the default implementation used by a LINQ query. LINQ to Objects is enabled including the System.Linq namespace.

XIII. LINQ to ADO.NET

LINQ to ADO.NET includes different LINQ implementations that share the need to manipulate relational data. It includes other technologies that are specific to each particular persistence layer:
  • LINQ to SQLHandles the mapping between custom types in C# and the physical table schema
  • LINQ to EntitiesIs in many ways similar to LINQ to SQL. However, instead of using the physical database as a persistence layer, it uses a conceptual Entity Data Model (EDM). The result is an abstraction layer that is independent from the physical data layer.
  • LINQ to DataSetMakes it possible to query a DataSet using LINQ

XIV. LINQ to XML

LINQ to XML offers a slightly different syntax that operates on XML data, allowing query and data manipulation.This query corresponds to the following C# 3.0 syntax:
var book =
new XElement( "Book",
new XAttribute( "Title", "Introducing LINQ" ), from person in team
where person.Role == "Author“ select new XElement( "Author", person.Name ) );

XV. C#2 and C#3 Important Language Features

1. C# 2.0 Revisited – Generics

You must be aware of this concept very well, but I wanted to cover this in my way taking simple examples.
Let’s take Min() function of C# for example,

Problem

The Min function, following is the issue:
int Min( int a, int b )
{ if (a < b) return a; else return b; }
object Min( object a, object b )
{ if (a < b) return a; else return b; }
IComparable Min( IComparable a, IComparable b )
{ if (a.CompareTo( b ) < 0) return a; else return b; }
int a = 5, b = 10;
int c = (int) Min( a, b );
I hope you got the issue, yes type casting.
C# 2.0 solved this problem with generics. The basic principle of generics is that type resolution is moved from the C# compiler to the jitter. Here is the generic version of the Min function:

Solution

T Min( T a, T b ) where T : IComparable {
                           if (a.CompareTo( b ) < 0) return a;
    else return b;
}

2. C# 2.0 Revisited – Delegates

delegate is a class that encapsulates one or more method. Internally, one delegate stores a list of method pointers, each of which can be paired with a reference to an instance of the class containing an instance method.
delegate can be declared as:
delegate void SimpleDelegate(); delegate int ReturnValueDelegate();
delegate void TwoParamsDelegate( string name, int age );
  • In C# 1.X, Delegates were instantiated as:
    public class DemoDelegate { void MethodA() { … }
    int MethodB() { … }

    void MethodC( string x, int y ) { … }

    void CreateInstance() {

    SimpleDelegate a = new SimpleDelegate( MethodA );
    ReturnValueDelegate b = new ReturnValueDelegate ( MethodB );

    TwoParamsDelegate c = new TwoParamsDelegate(

    MethodC ); // … } }

  • Delegate instantiation in C# 2.0:
    public class DemoDelegate
     {
    void MethodA() { … }

    int MethodB() { … }

    void MethodC( string x, int y ) { … }

    void CreateInstance() {
    SimpleDelegate a = MethodA;
    ReturnValueDelegate b = MethodB;
    TwoParamsDelegate c = MethodC; //
    }

    // … }

3. C# 2.0 Revisited – Anonymous Methods

  • Using an anonymous method:
    public class DemoDelegate {
    void Repeat10Times( SimpleDelegate someWork )
    { for (int i = 0; i < 10; i++) someWork(); }
    void Run2() {
    int counter = 0;
    this.Repeat10Times( delegate { Console.WriteLine("C# chapter" );
    counter++; } );
    Console.WriteLine( counter ); } // … }
  • Parameters for an anonymous method:
    public class DemoDelegate {

    void Repeat10Times( TwoParamsDelegate callback )
    { for (int i = 0; i < 10; i++)

    callback( Linq book”, i ); }

    void Run3() { Repeat10Times(

    delegate( string text, int age )

    { Console.WriteLine( {0} {1}”, text, age ); } );

    }

    // … }

4. C# 2.0 Revisited – Enumerators and Yield

a. IEnumerator and IEnumerable declarations

public interface IEnumerator
    {
bool MoveNext();
object Current { get; }
void Reset();
    }

public interface IEnumerable
{
IEnumerator GetEnumerator();
}

C# 2.0 introduced the yield statement through which the compiler automatically generates a class that implements the IEnumerator interface returned by the GetEnumerator method. The yield statement can be used only immediately before a return or break keyword. Enumeration using a yield statement:
public class CountdownYield : IEnumerable {
public int StartCountdown;

public IEnumerator GetEnumerator() {
for (int i = StartCountdown – 1; i >= 0; i–)
{
yield return i; }
}
}

b. Multiple yield statements

             public class CountdownYieldMultiple : IEnumerable
               {
                     public IEnumerator GetEnumerator() {

yield return 4;
yield return 3;
yield return 2;
yield return 1;
yield return 0;

}
}

c. Enumeration using yield (typed)

public class CountdownYieldTypeSafe : IEnumerable<int> {
public int StartCountdown;

IEnumerator IEnumerable.GetEnumerator() { return this.GetEnumerator(); }

public IEnumerator<int> GetEnumerator() {

for (int i = StartCountdown – 1; i >= 0; i–)

{ yield return i; }
}
}

5. C# 3.0 Features – Local Type Inference

C# 3.0 offers type inference that allows us to define a variable by using the var keyword instead of a specific type. This might seem to be equivalent to defining a variable of type object, but it is not.
     var a = 2; //a is declared as int
     object b = 2; // Boxing an int into an object
     int C = a; // No cast, no unboxing
     int D = (int)b // Cast is required, an unboxing is done
  • When var is used, the compiler infers the type from the expression used to initialize the variable. The compiled IL code contains only the inferred type.
  • In other words, consider this code:
      int a = 5;
      var b = a;
  • It is perfectly equivalent to this example:
      int a = 5;
      int b = a;
  • The var keyword can be used only within a local scope.
  • In other words, a local variable can be defined in this way, but not a member or a parameter.
  • The following code shows some examples of valid uses of var:
    public void ValidUse( decimal d )
      {
        var x = 2.3; // double
    
        var y = x; // double
        var r = x / y; // double
    
        var s = "sample"; // string
        var l = s.Length; // int
        var w = d; // decimal
    
        var p = default(string); // string
    }
  • The sample shows some cases in which the var keyword is not allowed:
    class VarDemo {

    // invalid token ‘var’ in class, struct or interface member declaration

    var k =0;

    // type expected in parameter list

    public void InvalidUseParameter( var x ){} // type expected in result type declaration
    public var InvalidUseResult() { return 2; }

    public void InvalidUseLocal() {

    var x; // Syntax error, ‘=’ expected

    var y = null; // Cannot infer local variable type from ‘null’
    }
    // … }

6. C# 3.0 Features – Lambda Expressions

C# 2.0 introduced the capability to “pass a pointer to some code” as a parameter by using anonymous methods. This concept is a powerful one, but what you really pass in this way is a reference to a method, not exactly a piece of code. That reference points to strongly typed code that is generated at compile time. Using generics, we can obtain more flexibility, but it is hard to apply standard operators to a generic type.
C# 3.0 introduces lambda expressions, which allow the definition of anonymous methods using more concise syntax. Lambda expressions can also optionally postpone code generation by creating an expression tree that allows further manipulation before code is actually generated, which happens at execution time.
Lambda expression examples:
• ( int a, int b ) => { return a + b; } // Explicitly typed, statement body
• ( int a, int b ) => a + b; // Explicitly typed, expression body

• ( a, b ) => { return a + b; } // Implicitly typed, statement body
• ( a, b ) => a + b // Implicitly typed, expression body

• ( x ) => sum += x // Single parameter with parentheses
• x => sum += x // Single parameter no parentheses

• () => sum + 1 // No parameters
Some lambda expressions have a particular name based on their purpose. A predicate is a Boolean expression that is intended to indicate membership of an element in a group. For example, it is used to define how to filter items inside a loop:
// Predicate

 age ) => age > 21
A projection is an expression that returns a type different from the type of its single parameter:
// Projection: takes a string and returns an int
 ( s ) => s.Length
  • Lambda expression as a predicate:
    public static void Demo() {
    string[] names = { "Marco", "Paolo", "Tom" }; 
    Display( names, s => s.Length > 4 ); }
    public static void Display( T[] names, Func<T, bool> filter ){
    foreach( T s in names) {
    if (filter( s )) Console.WriteLine( s ); }
    }
  • A lambda expression can also be assigned to a variable of these delegate types:
    public delegate T Func();
    public delegate T Func( A0 arg0 );
    public delegate T Func( A0 arg0, A1 arg1 );
    public delegate T Func( A0 arg0, A1 arg1, A2 arg2 );
    public delegate T Func( A0 arg0, A1 arg1, A2 arg2, A3 arg3 );

7. C# 3.0 Features – Extension Methods

C# 3.0 introduces a syntax that conceptually extends an existing type (either reference or value) by adding new methods without deriving it into a new type. The methods that extend a type can use only the public members of the type itself, just as you can do from any piece of code outside the target type.
An extension method must be static and public, must be declared inside a static class, and must have the keyword this before the first parameter type, which is the type that the method extends.
Extension methods are public because they can be (and normally are) called from outside the class where they are declared.
However, the result type of the extension method might be the extended type itself.
LINQ very frequently uses extension methods in this way.
The following code shows a traditional approach to writing two methods (FormattedUS and FormattedIT) that converts a decimal value into a string formatted with a specific culture:
static class Traditional {
public static void Demo() {
decimal x = 1234.568M;
Console.WriteLine( FormattedUS( x ) );

Console.WriteLine( FormattedIT( x ) );
}

public static string FormattedUS( decimal d ) {
return String.Format( formatIT, {0:#,0.00}”, d );
}
public static string FormattedIT( decimal d ) {
return String.Format( formatUS, {0:#,0.00}”, d );
}

static CultureInfo formatUS = new CultureInfo( en-US” );
static CultureInfo formatIT = new CultureInfo( it-IT” );
}

a. Extension methods declaration

using System;
using System.Globalization;

internal static class ExtensionMethods
{
public static void Demo()
{
decimal x = 1234.568M;
Console.WriteLine(x.FormattedUS());
Console.WriteLine(x.FormattedIT());
Console.WriteLine(FormattedUS(x)); // Traditional call allowed
Console.WriteLine(FormattedIT(x));// Traditional call allowed
}

private static CultureInfo formatUS = new CultureInfo(en-US”);
private static CultureInfo formatIT = new CultureInfo(it-IT”);

public static string FormattedUS(this decimal d)
{
return String.Format(formatIT, {0:#,0.00}”, d);
}

public static string FormattedIT(this decimal d)
{
return String.Format(formatUS, {0:#,0.00}”, d);
}
}

b. Extension methods for native value types

static class ExtensionMethods {
public static decimal Double( this decimal d ) { return d + d; }
public static decimal Triple( this decimal d ) { return d * 3; }
public static decimal Increase( this decimal d ) { return ++d; }
public static decimal Decrease( this decimal d ) { return --d; }
public static decimal Half( this decimal d ) { return d / 2; } //}
Extension methods call order:
decimal x=14M,y= 14M;
x = Half(Triple(Decrease(Decrease(Double(Increase(x) )))) );
y = y.Increase().Double().Decrease().Decrease().Triple().Half( );
  • An extension method is not automatically considered. Its resolution follows some rules.
  • Here is the order of evaluation used to resolve a method for an identifier.
  • Instance method: If an instance method exists, it has priority.
  • Extension method: The search for an extension method is made through all static classes in the “current namespace” and in all namespaces included in active using directives.

c. Extension methods resolution

public class A
{
    public virtual void X() { }
}
public class B : A
{
    public override void X() { }
    public void Y() { }
}
static public class E
{
    static void X(this A a) { }
    static void Y(this A b) { }
    public static void Demo() {
A a = new A();
B b = new B();
A c = new B();
a.X(); // Call A.X
b.X(); // Call B.X
c.X(); // Call B.X
a.Y(); // Call E.Y
b.Y(); // Call B.Y
c.Y(); // Call E.Y }
}

d. Lambda expression as predicate

public static void Display( this T[] names, Func<T, bool> filter ) {…}

public static void Demo() {

string[] names = { Marco”, Paolo”, Tom” };
names.Display( s => s.Length > 4 );// It was: Display( names, s => s.Length > 4 );

}

8. C# 3.0 Features – Object Initialization Expressions

C# 3.0 introduces a shorter form of object initialization syntax that generates functionally equivalent code:
// Implicitly calls default constructor before object initialization
Customer customer = new Customer { Name = "Marco", Country = "Italy" };

a. Explicit constructor call in object initializer

// Explicitly specify constructor to call before object initialization
Customer c1 = new Customer() { Name = "Marco", Country = "Italy" };
// Explicitly specify nondefault constructor
Customer c2 = new Customer( "Paolo", 21 ) { Country = "Italy" };

b. Nested object initializers

public class Point
{
    private int x, y;

public int X
{
get { return x; }
set { x = value; }
}

public int Y
{
get { return y; }
set { y = value; }
}
}

public class Rectangle
{
private Point tl, br;

public Point TL
{
get { return tl; }
set { tl = value; }
}

public Point BR
{
get { return br; }
set { br = value; }
}
}

// Possible code inside a method
Rectangle r = new Rectangle { TL = new Point { X = 0, Y = 1 },BR = new Point { X = 2, Y = 3 } };

c. Initializers for owned objects

public class Rectangle { Point tl = new Point(); Point br = new Point();

public Point TL { get { return tl; } } public Point BR { get { return br; } } }

// Possible code inside a method
Rectangle r = new Rectangle { TL = { X = 0, Y = 1 },BR = { X = 2, Y = 3 } };

d. Collection initializers

//Collection classes that implement ICollection
List<int> integers = new List<int> { 1, 3, 9, 18 };
List list = new List {

new Customer( Jack”, 28 ) { Country = USA”}, new Customer { Name = Paolo” },

new Customer { Name = Marco”, Country = Italy” }
};

//Collection classes that implement IEnumerable
ArrayList integers = new ArrayList() { 1, 3, 9, 18 };
ArrayList list = new ArrayList {

new Customer( Jack”, 28 ) { Country = USA”}, new Customer { Name = Paolo” },

new Customer { Name = Marco”, Country = Italy” }
};

9. C# 3.0 Features – Anonymous Types

An object initializer can also be used without specifying the class that will be created with the new operator.
Doing that, a new class-an anonymous type-is created.
Consider the example shown below:
Customer c1 = new Customer { Name = "Marco" };
 var c2 = new Customer { Name = "Paolo" };

var c3 = new { Name = Tom”, Age = 31 };
var c4 = new { c2.Name, c2.Age };

var c5 = new { c1.Name, c1.Country };
var c6 = new { c1.Country, c1.Name };

When you do GetType() – the following is the output that is generated:
c1 is Customer c2 is Customer c3 is:
f__AnonymousType0`2[System.String,System.Int32] c4 is
f__AnonymousType0`2[System.String,System.Int32] c5 is
 f__AnonymousType5`2[System.String,System.String] c6 is
f__AnonymousTypea`2[System.String,System.String]

10. C# 3.0 Features – Query Expressions

C# 3.0 also introduces query expressions, which have a syntax similar to the SQL language and are used to manipulate data. This syntax is converted into regular C# 3.0 syntax that makes use of specific classes, methods, and interfaces that are part of the LINQ libraries.

XVI. LINQ Syntax Fundamentals

1. LINQ Query Expression

The following code shows a prototype of the full syntax of a LINQ query expression:
query-expression ::=
from-clause query-body query-body
::= join-clause* (from-clause join-clause* | let-clause | where-clause)*
orderby-clause? (select-clause | groupby-clause) query-continuation?
from-clause ::= from itemName in srcExpr _
select-clause ::= select selExpr groupby-clause ::= group selExpr by keyExpr
The first from clause can be followed by zero or more fromlet, or where clauses.
let clause applies a name to the result of an expression, while a where clause defines a filter that will be applied to include specific items in the results. Each from clause is a generator that represents an iteration over a sequence on which query operators (such as the extension methods of System.Linq.Enumerable) are applied.
let-clause ::= let itemName = selExpr where-clause ::= where predExpr
from clause can be followed by any number of join clauses. The final select or group clause can be preceded by an orderby clause that applies an ordering to the results:
join-clause ::= join itemName in srcExpr on keyExpr equals keyExpr (into itemName)?

orderby-clause ::= orderby (keyExpr (ascending | descending)?)* _
query-continuation ::= into itemName query-body.

XVII. Conclusion

Long post, I guess we covered a lot of concepts deeply. You can learn more theory from MSDN or other renowned community sites. We covered very important and deep concepts of LINQ, C#2.0 and C# 3.0.
Happy coding!
To read more informative articles on C#, ASP.NET and MVC, follow A Practical Approach.

Continue reading “LINQ Interview Questions (All in One)”

Web Services and Windows Services Interview Questions


WebServices And Windows Services

Can you give an example of when it would be appropriate to use a web service as opposed to non-serviced .NET component
Web service is one of main component in Service Oriented Architecture. You could use web services when your clients and servers are running on different networks and also different platforms. This provides a loosely coupled system. And also if the client is behind the firewall it would be easy to use web service since it runs on port 80 (by default) instead of having some thing else in Service Oriented Architecture applications.
What is the standard you use to wrap up a call to a Web service
“SOAP.

What is the transport protocol you use to call a Web service SOAP HTTP with SOAP
What does WSDL stand for? “WSDL stands for Web Services Dsescription Langauge. There is WSDL.exe that creates a .wsdl Files which defines how an XML Web service behaves and instructs clients as to how to interact with the service.
eg: wsdl http://LocalHost/WebServiceName.asmx
Where on the Internet would you look for Web Services?http://www.uddi.org

What does WSDL stand for? Web Services Description Language

True or False: To test a Web service you must create a windows application or Web application to consume this service? False.

What are the various ways of accessing a web service ?

1.Asynchronous Call
Application can make a call to the Webservice and then continue todo watever oit  wants to do.When the service is ready it will notify the application.Application  can use BEGIN and END method to make asynchronous call to the webmethod.We can use  either a WaitHandle or a Delegate object when making asynchronous call.
The WaitHandle class share resources between several objects. It provides several  methods which will wait for the resources to become available
The easiest and most powerful way to to implement an asynchronous call is using a  delegate object. A delegate object wraps up a callback function. The idea is to  pass a method in the invocation of the web method. When the webmethod has finished  it will call this callback function to process the result
2.Synchronous Call
Application has to wait until execution has completed.
 Note: Few of the references are taken from other sites/sources
 
What are VSDISCO files?VSDISCO files are DISCO files that support dynamic discovery of Web services. If you place the following VSDISCO file in a directory on your Web server, for example, it returns   references to all ASMX and DISCO files in the host directory and any subdirectories not noted in elements:
                <DYNAMICDISCOVERY
                  xmlns="urn:schemas-dynamicdiscovery:disco.2000-03-17">
                  <EXCLUDE path="_vti_cnf" />
                  <EXCLUDE path="_vti_pvt" />
                  <EXCLUDE path="_vti_log" />
                  <EXCLUDE path="_vti_script" />
                  <EXCLUDE path="_vti_txt" />
                </DYNAMICDISCOVERY>
 
How does dynamic discovery work?ASP.NET maps the file name extension VSDISCO to an HTTP handler that scans the host  directory and subdirectories for ASMX and DISCO files and returns a dynamically generated DISCO document. A client who requests a VSDISCO file gets back what appears to be a static DISCO document.
Note that VSDISCO files are disabled in the release version of ASP.NET. You can reenable them by uncommenting the line   in the section of Machine.config that maps *.vsdisco to System.Web.Services.Discovery.DiscoveryRequestHandler and granting the ASPNET  user account permission to read the IIS metabase. However, Microsoft is actively discouraging the use of VSDISCO files because they could represent a threat to Web server security.
 
Is it possible to prevent a browser from caching an ASPX page?
Just call SetNoStore on the HttpCachePolicy object exposed through the Response object’s Cache property, as demonstrated here:
        <%@ Page Language="C#" %>

<%
Response.Cache.SetNoStore ();
Response.Write (DateTime.Now.ToLongTimeString ());
%>

SetNoStore works by returning a Cache-Control: private, no-store header in the HTTP response. In this example, it prevents caching of a Web page that shows the current time.
What does AspCompat=”true” mean and when should I use it?
AspCompat is an aid in migrating ASP pages to ASPX pages. It defaults to false but should be set to true in any ASPX file that creates apartment-threaded COM objects–that is, COM objects registered ThreadingModel=Apartment. That includes all COM objects written with  Visual Basic 6.0. AspCompat should also be set to true (regardless of threading  model)  if the page creates COM objects that access intrinsic ASP objects such as Request and Response. The following directive sets AspCompat to true:
 <%@ Page AspCompat="true" %>
Setting AspCompat to true does two things. First, it makes intrinsic ASP objects available      to the COM components by placing unmanaged wrappers around the equivalent ASP.NET objects. Second, it improves the performance of calls that the page places to apartment- threaded COM objects by ensuring that the page (actually, the thread that processes the  request for the page) and the COM objects it creates share an apartment. AspCompat=”true” forces ASP.NET request threads into single-threaded apartments (STAs). If those threads create COM objects marked ThreadingModel=Apartment, then the objects are created in the same STAs as the threads that created them. Without AspCompat=”true,” request threads run in a multithreaded apartment (MTA) and each call to an STA-based COM object incurs a performance hit when it’s  marshaled across apartment boundaries.
Do not set AspCompat to true if your page uses no COM objects or if it uses COM objects that don’t access ASP intrinsic objects and that are registered ThreadingModel=Free or  ThreadingModel=Both.
Can two different programming languages be mixed in a single ASMX file?
No.
 
What namespaces are imported by default in ASMX files?
The following namespaces are imported by default. Other namespaces must be imported manually.· System, System.Collections,System.ComponentModel,System.Data, System.Diagnostics,System.Web,System.Web.Services
How do I provide information to the Web Service when the information is required as a SOAP Header?
The key here is the Web Service proxy you created using wsdl.exe or through Visual Studio .NET’s Add Web Reference menu option. If you happen to download a WSDL file for a Web Service that requires a SOAP header, .NET will create a SoapHeader class in the proxy source file. Using the previous example:
      public class Service1 : System.Web.Services.Protocols.SoapHttpClientProtocol
        {   
            public AuthToken AuthTokenValue;

[System.Xml.Serialization.XmlRootAttribute(Namespace=http://tempuri.org/&#8221;, IsNullable=false)]
public class AuthToken : SoapHeader { public string Token; }}

In this case, when you create an instance of the proxy in your main application file, you’ll also create an instance of the AuthToken class and assign the string:

     Service1 objSvc = new Service1();
     processingobjSvc.AuthTokenValue = new AuthToken();
     objSvc.AuthTokenValue.Token = <ACTUAL token value>;
     Web Servicestring strResult = objSvc.MyBillableWebMethod();
 
What is WSDL?
WSDL is the Web Service Description Language, and it is implemented as a specific XML vocabulary. While it’s very much more complex than what can be described here, there are two important aspects to WSDL with which you should be aware. First, WSDL provides instructions to consumers of Web Services to describe the layout and contents of the SOAP packets  the Web Service intends to issue. It’s an interface description document, of sorts. And second, it isn’t intended that you  read and interpret the WSDL. Rather, WSDL should be processed by machine, typically to generate proxy source code (.NET) or create dynamic proxies on the fly (the SOAP Toolkit or Web Service Behavior).
What is a Windows Service and how does its lifecycle differ from a “standard” EXE?
Windows service is a application that runs in the background. It is equivalent to a NT service.
The executable created is not a Windows application, and hence you can’t just click and run it . it needs to be installed as a service, VB.Net has a facility where we can add an installer to our program and then use a utility to install the service. Where as this is not the case with standard exe

How can a win service developed in .NET be installed or used in Win98?
Windows service cannot be installed on Win9x machines even though the .NET framework runs on machine.

 
Can you debug a Windows Service? How ? 
Yes we can debug a Windows Service.
Attach the WinDbg debugger to a service after the service starts
This method is similar to the method that you can use to attach a debugger to a process and then debug a process.
Use the process ID of the process that hosts the service that you want to debug
  1. To determine the process ID (PID) of the process that hosts the service that you want to debug, use one of the following methods.
    • Method 1: Use the Task Manager
      1. Right-click the taskbar, and then click Task Manager. The Windows Task Manager dialog box appears.
      2. Click the Processes tab of the Windows Task Manager dialog box.
      3. Under Image Name, click the image name of the process that hosts the service that you want to debug. Note the process ID of this process as specified by the value of the corresponding PID field.
    • Method 2: Use the Task List Utility (tlist.exe)
      1. Click Start, and then click Run. The Run dialog box appears.
      2. In the Open box, type cmd, and then click OK.
      3. At the command prompt, change the directory path to reflect the location of the tlist.exe file on your computer.Note The tlist.exe file is typically located in the following directory: C:\Program Files\Debugging Tools for Windows
      4. At the command prompt, type tlist to list the image names and the process IDs of all processes that are currently running on your computer.

    Note Make a note of the process ID of the process that hosts the service that you want to debug.

  2. At a command prompt, change the directory path to reflect the location of the windbg.exe file on your computer.Note If a command prompt is not open, follow steps a and b of Method 1. The windbg.exe file is typically located in the following directory: C:\Program Files\Debugging Tools for Windows.
  3. At the command prompt, type windbg –p ProcessID to attach the WinDbg debugger to the process that hosts the service that you want to debug.
Note ProcessID is a placeholder for the process ID of the process that hosts the service that you want to debug.

Use the image name of the process that hosts the service that you want to debug

You can use this method only if there is exactly one running instance of the process that hosts the service that you want to run. To do this, follow these steps:

  1. Click Start, and then click Run. The Run dialog box appears.
  2. In the Open box, type cmd, and then click OK to open a command prompt.
  3. At the command prompt, change the directory path to reflect the location of the windbg.exe file on your computer.Note The windbg.exe file is typically located in the following directory: C:\Program Files\Debugging Tools for Windows.
  4. At the command prompt, type windbg –pn ImageName to attach the WinDbg debugger to the process that hosts the service that you want to debug.
NoteImageName is a placeholder for the image name of the process that hosts the service that you want to debug. The “-pn” command-line option specifies that the ImageName command-line argument is the image name of a process. back to the top
Start the WinDbg debugger and attach to the process that hosts the service that you want to debug
  1. Start Windows Explorer.
  2. Locate the windbg.exe file on your computer.Note The windbg.exe file is typically located in the following directory: C:\Program Files\Debugging Tools for Windows
  3. Run the windbg.exe file to start the WinDbg debugger.
  4. On the File menu, click Attach to a Process to display the Attach to Process dialog box.
  5. Click to select the node that corresponds to the process that hosts the service that you want to debug, and then click OK.
  6. In the dialog box that appears, click Yes to save base workspace information. Notice that you can now debug the disassembled code of your service.
Configure a service to start with the WinDbg debugger attached
You can use this method to debug services if you want to troubleshoot service-startup-related problems.
1 Configure the “Image File Execution” options. To do this, use one of the following methods:
  • Method 1: Use the Global Flags Editor (gflags.exe)
    1. Start Windows Explorer.
    2. Locate the gflags.exe file on your computer.Note The gflags.exe file is typically located in the following directory: C:\Program Files\Debugging Tools for Windows.
    3. Run the gflags.exe file to start the Global Flags Editor.
    4. In the Image File Name text box, type the image name of the process that hosts the service that you want to debug. For example, if you want to debug a service that is hosted by a process that has MyService.exe as the image name, type MyService.exe.
    5. Under Destination, click to select the Image File Options option.
    6. Under Image Debugger Options, click to select the Debugger check box.
    7. In the Debugger text box, type the full path of the debugger that you want to use. For example, if you want to use the WinDbg debugger to debug a service, you can type a full path that is similar to the following: C:\Program Files\Debugging Tools for Windows\windbg.exe
      h. Click Apply, and then click OK to quit the Global Flags Editor.
  • Method 2: Use Registry Editor
    1. Click Start, and then click Run. The Run dialog box appears.
    2. In the Open box, type regedit, and then click OK to start Registry Editor.
    3. Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.In Registry Editor, locate, and then right-click the following registry subkey:
      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options
    4. Point to New, and then click Key. In the left pane of Registry Editor, notice that New Key #1 (the name of a new registry subkey) is selected for editing.
    5. Type ImageName to replace New Key #1, and then press ENTER.Note ImageName is a placeholder for the image name of the process that hosts the service that you want to debug. For example, if you want to debug a service that is hosted by a process that has MyService.exe as the image name, type MyService.exe.
    6. Right-click the registry subkey that you created in step e.
    7. Point to New, and then click String Value. In the right pane of Registry Editor, notice that New Value #1, the name of a new registry entry, is selected for editing.
    8. Replace New Value #1 with Debugger, and then press ENTER.
    9. Right-click the Debugger registry entry that you created in step h, and then click Modify. The Edit String dialog box appears.
    10. In the Value data text box, type DebuggerPath, and then click OK.

    Note DebuggerPath is a placeholder for the full path of the debugger that you want to use. For example, if you want to use the WinDbg debugger to debug a service, you can type a full path that is similar to the following: C:\Program Files\Debugging Tools for Windows\windbg.exe

2 For the debugger window to appear on your desktop, and to interact with the debugger, make your service interactive. If you do not make your service interactive, the debugger will start but you cannot see it and you cannot issue commands. To make your service interactive, use one of the following methods:
  • Method 1: Use the Services console
    1. Click Start, and then point to Programs.
    2. On the Programs menu, point to Administrative Tools, and then click Services. The Services console appears.
    3. In the right pane of the Services console, right-click ServiceName, and then click Properties.Note ServiceName is a placeholder for the name of the service that you want to debug.
    4. On the Log On tab, click to select the Allow service to interact with desktop check box under Local System account, and then click OK.
  • Method 2: Use Registry Editor
    1. In Registry Editor, locate, and then click the following registry subkey:HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ServiceName
      Note Replace ServiceName with the name of the service that you want to debug. For example, if you want to debug a service named MyService, locate and then click the following registry key:
      HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MyService
    2. Under the Name field in the right pane of Registry Editor, right-click Type, and then click Modify. The Edit DWORD Value dialog box appears.
    3. Change the text in the Value data text box to the result of the binary OR operation with the binary value of the current text and the binary value, 0x00000100, as the two operands. The binary value, 0x00000100, corresponds to the SERVICE_INTERACTIVE_PROCESS constant that is defined in the WinNT.h header file on your computer. This constant specifies that a service is interactive in nature.
3 When a service starts, the service communicates to the Service Control Manager how long the service must have to start (the time-out period for the service). If the Service Control Manager does not receive a “service started” notice from the service within this time-out period, the Service Control Manager terminates the process that hosts the service. This time-out period is typically less than 30 seconds. If you do not adjust this time-out period, the Service Control Manager ends the process and the attached debugger while you are trying to debug. To adjust this time-out period, follow these steps:
  1. In Registry Editor, locate, and then right-click the following registry subkey: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control
  2. Point to New, and then click DWORD Value. In the right pane of Registry Editor, notice that New Value #1 (the name of a new registry entry) is selected for editing.
  3. Type ServicesPipeTimeout to replace New Value #1, and then press ENTER.
  4. Right-click the ServicesPipeTimeout registry entry that you created in step c, and then click Modify. The Edit DWORD Value dialog box appears.
  5. In the Value data text box, type TimeoutPeriod, and then click OKNote TimeoutPeriod is a placeholder for the value of the time-out period (in milliseconds) that you want to set for the service. For example, if you want to set the time-out period to 24 hours (86400000 milliseconds), type 86400000.
  6. Restart the computer. You must restart the computer for Service Control Manager to apply this change.
4 Start your Windows service. To do this, follow these steps:
  1. Click Start, and then point to Programs.
  2. On the Programs menu, point to Administrative Tools, and then click Services. The Services console appears.
  3. In the right pane of the Services console, right-click ServiceName, and then click Start.
Note ServiceName is a placeholder for the name of the service that you want to debug.
 Note: Few of the references are taken from other sites/sources
http://www.planet-source-code.com/vb/scripts/ShowCode.asp?txtCodeId=3631&lngWId=10

C# and Asp.Net Questions (All in one)


Introduction

My this article provides a collection of numerous .Net, C#, ADO.NET, Web Services, .Net Framework questions and answers for which a reader has to look around for entire internet on different community web sites. Most of the questions and answers you must have already read. The purpose of this article is to consolidate at the most study material related to .Net at one single place.

ASP.NET

What is view state and use of it?The current property settings of an ASP.NET page and those of any ASP.NET server controls contained within the page. ASP.NET can detect when a form is requested for the first time versus when the form is posted (sent to the server), which  allows you to program accordingly.

What are user controls and custom controls?Custom controls:
 A control authored by a user or a third-party software vendor that does not belong to   the .NET Framework class library. This is a generic term that includes user controls. A  custom server control is used in Web Forms (ASP.NET pages). A custom client control is used  in Windows Forms applications.

User Controls:
In ASP.NET: A user-authored server control that enables an ASP.NET page to be re-used   as a server control. An ASP.NET user control is authored declaratively  and persisted as a  text file with an .ascx extension. The ASP.NET page framework compiles a user control on  the fly to a class that derives from the        System.Web.UI.UserControl class.

What are the validation controls?A set of server controls included with ASP.NET that test user input in HTML and Web server  controls for programmer-defined requirements. Validation controls perform input checking in server code. If the user is working with a browser that supports DHTML, the validation  controls can also perform validation using client script.

What’s the difference between Response.Write() andResponse.Output.Write()?The latter one allows you to write formattedoutput.

What methods are fired during the page load? Init () When the page is instantiated, Load() – when the page is loaded into server  memory,PreRender () – the brief moment before the page is displayed to the user  as HTML, Unload() – when page finishes loading.

Where does the Web page belong in the .NET Framework class hierarchy?System.Web.UI.Page

Where do you store the information about the user’s locale?System.Web.UI.Page.Culture

What’s the difference between Codebehind=”MyCode.aspx.cs” and Src=”MyCode.aspx.cs”?CodeBehind is relevant to Visual Studio.NET only.

What’s a bubbled event?
When you have a complex control, like DataGrid, writing an event processing routine for each object (cell, button,row, etc.) is quite tedious. The controls can bubble up their eventhandlers, allowing the main DataGrid event handler to take care of its constituents.
Suppose you want a certain ASP.NET function executed on MouseOver over a certain button.

Where do you add an event handler?It’s the Attributesproperty, the Add function inside that property.            
e.g. btnSubmit.Attributes.Add(“onMouseOver”,”someClientCode();”)

What data type does the RangeValidator control support?Integer,String and Date.

What are the different types of caching?
Caching is a technique widely used in computing to increase performance by keeping frequently accessed or expensive data in memory. In context of web application, caching is used to retain the pages or data across HTTP requests and reuse them without the expense of recreating them.ASP.NET has 3 kinds of caching strategiesOutput CachingFragment CachingData    

CachingOutput Caching: Caches the dynamic output generated by a request. Some times it is useful to cache  the output of a website even for a minute, which will result in a better  performance. For caching the whole page the page should have OutputCache directive.
Fragment Caching: Caches the portion of the  page generated by the request. Some times it is not practical to cache the entire page, in such cases we can cache a portion of page

Data Caching: Caches the objects programmatically. For     data caching asp.net provides a cache object for eg: cache[“States”] = dsStates;

What do you mean by authentication and authorization?Authentication is the process of validating a user on the credentials (username and     password) and authorization performs after authentication. After Authentication a user will     be verified for performing the various tasks, It access is limited it is known as       authorization.

What are different types of directives in .NET?
@Page: Defines page-specific attributes used by the ASP.NET page parser and compiler. Can       be included only in .aspx files   
@Control:Defines control-specific attributes used by the ASP.NET page parser and        compiler. Can be included only in .ascx files.
@Import: Explicitly imports a namespace into a page or user control. The Import         directive cannot have more than one namespace attribute. To import multiple     namespaces,     use multiple @Import directives.
@Implements: Indicates that the current page or user control implements the specified .NET      framework interface.
@Register: Associates aliases with namespaces and class names for concise notation in   custom server control syntax.
@Assembly: Links an assembly to the current page during compilation, making all         the     assembly’s classes and interfaces available for use on the      page.
@OutputCache: Declaratively controls the output caching policies of an ASP.NET page or a        user control contained in a page
@Reference: Declaratively indicates that another user control or page source file               should be dynamically compiled and linked against the page in which this directive is   declared.

Note: Few of the references are taken from other sites/sources


How do I debug an ASP.NET application that wasn’t written with Visual Studio.NET and that doesn’t use code-behind?Start the DbgClr debugger that comes with the .NET Framework SDK, open the file containing      the code you want to debug, and set your breakpoints. Start the ASP.NET application. Go back to DbgClr, choose Debug Processes from the Tools menu, and select  aspnet_wp.exe from  the list of processes. (If aspnet_wp.exe doesn’t appear in the list,check the “Show system      processes” box.) Click the Attach button to attach to aspnet_wp.exe and begin debugging.
Be sure to enable debugging in the ASPX file before debugging it with DbgClr. You can   enable tell ASP.NET to build debug executables by placing a
   statement at the top of an ASPX file or a   statement in a Web.config file.

Can a user browsing my Web site read my Web.config or Global.asax files?
No. The section of Machine.config, which holds the master configuration  settings for ASP.NET, contains entries that map ASAX files, CONFIG files, and selected  other file types to an HTTP handler named HttpForbiddenHandler, which fails attempts to retrieve the associated file. You can modify it by editing  Machine.config or including an section in a local Web.config file.

What’s the difference between Page.RegisterClientScriptBlock and Page.RegisterStartupScript?RegisterClientScriptBlock is for returning blocks of client-side script containing functions. RegisterStartupScript is for returning blocks of client-script not   packaged in functions-in other words, code that’s to execute when the page is loaded. The latter positions script blocks near the end of the document so elements on the page that the script interacts are loaded before the script runs.

Is it necessary to lock application state before accessing it?Only if you’re performing a multistep update and want the update to be treated as an atomic     operation. Here’s an example:

Application.Lock ();
                Application["ItemsSold"] = (int) Application["ItemsSold"] + 1;
                Application["ItemsLeft"] = (int) Application["ItemsLeft"] - 1;
                Application.UnLock ();


By locking application state before updating it and unlocking it afterwards, you ensure  that another request being processed on another thread doesn’t read application state   at exactly the wrong time and see an inconsistent view of it. If I update session state, should I lock it, too? Are concurrent accesses by multiple requests executing on multiple threads a concern with session state?
Concurrent accesses aren’t an issue with session state, for two reasons. One, it’s unlikely that two requests from the same user will overlap. Two, if they do overlap, ASP.NET locks down session state during request processing so that two threads can’t touch it at once. Session state is locked down when the HttpApplication instance that’s processing the request fires an AcquireRequestState event and unlocked when it fires a ReleaseRequestState event.

Do ASP.NET forms authentication cookies provide any protection against replay attacks? Do they, for example, include the client’s IP  address or anything else that would distinguish the real client from an attacker?
No. If an authentication cookie is stolen, it can be used by an attacker. It’s up to you to     prevent this from happening by using an encrypted communications channel (HTTPS). Authentication cookies issued as session cookies, do, however,include a time-out valid that     limits their lifetime. So a stolen session cookie can only be used in replay attacks as long as the ticket inside the cookie is valid. The default time-out interval is 30 minutes.You can change that by modifying the timeout attribute accompanying the element in Machine.config or a local Web.config file. Persistent authentication cookies do not  time-out and therefore are a more serious security threat if stolen.
How do I send e-mail from an ASP.NET application?
MailMessage message = new MailMessage ();
        message.From = ;
        message.To = ;
        message.Subject = "Scheduled Power Outage";
        message.Body = "Our servers will be down tonight.";
        SmtpMail.SmtpServer = "localhost";
        SmtpMail.Send (message);
 MailMessage and SmtpMail are classes defined in the .NET Framework Class Library’s  System.Web.Mail namespace. Due to a security change made to ASP.NET just before it shipped,  you need to set SmtpMail’s SmtpServer property to “localhost” even though “localhost” is  the default. In addition, you must use the IIS configuration applet to enable localhost  (127.0.0.1) to relay messages through the local SMTP service.
What are VSDISCO files?
VSDISCO files are DISCO files that support dynamic discovery of Web services. If you place the following VSDISCO file in a directory on your Web server, for example, it returns   references to all ASMX and DISCO files in the host directory and any subdirectories not         noted in elements:
<?xml version="1.0" ?>
<dynamicDiscovery
xmlns="urn:schemas-dynamicdiscovery:disco.2000-03-17">
<exclude path="_vti_cnf" />
<exclude path="_vti_pvt" />
<exclude path="_vti_log" />
<exclude path="_vti_script" />
<exclude path="_vti_txt" />
</dynamicDiscovery>
 

How does dynamic discovery work?
ASP.NET maps the file name extension VSDISCO to an HTTP handler that scans the host  directory and subdirectories for ASMX and DISCO files and returns a dynamically generated DISCO document. A client who requests a VSDISCO file gets back what appears to be a static DISCO document.
Note that VSDISCO files are disabled in the release version of ASP.NET. You can reenable them by uncommenting the line   in the section of Machine.config that maps *.vsdisco to System.Web.Services.Discovery.DiscoveryRequestHandler and granting the ASPNET  user account permission to read the IIS metabase. However, Microsoft is actively discouraging the use of VSDISCO files because they could represent a threat to Web server security.

Is it possible to prevent a browser from caching an ASPX page?
Just call SetNoStore on the HttpCachePolicy object exposed through the Response object’s Cache property, as demonstrated here:

<%@ Page Language="C#" %>
<html>
<body>
<%
              Response.Cache.SetNoStore ();
              Response.Write (DateTime.Now.ToLongTimeString ());
%>
</body>
</html>
SetNoStore works by returning a Cache-Control: private, no-store header in the HTTP response. In this example, it prevents caching of a Web page that shows the current time.
 
What does AspCompat=”true” mean and when should I use it?
AspCompat is an aid in migrating ASP pages to ASPX pages. It defaults to false but should be set to true in any ASPX file that creates apartment-threaded COM objects–that is, COM objects registered ThreadingModel=Apartment. That includes all COM objects written with  Visual Basic 6.0. AspCompat should also be set to true (regardless of threading  model)  if the page creates COM objects that access intrinsic ASP objects such as Request and Response. The following directive sets AspCompat to true:
<%@ Page AspCompat="true" %>
Setting AspCompat to true does two things. First, it makes intrinsic ASP objects available      to the COM components by placing unmanaged wrappers around the equivalent ASP.NET objects. Second, it improves the performance of calls that the page places to apartment- threaded COM objects by ensuring that the page (actually, the thread that processes the  request for the page) and the COM objects it creates share an apartment. AspCompat=”true” forces ASP.NET request threads into single-threaded apartments (STAs). If those threads create COM objects marked ThreadingModel=Apartment, then the objects are created in the same STAs as the threads that created them. Without AspCompat=”true,” request threads run in a multithreaded apartment (MTA) and each call to an STA-based COM object incurs a performance hit when it’s  marshaled across apartment boundaries.
Do not set AspCompat to true if your page uses no COM objects or if it uses COM objects that don’t access ASP intrinsic objects and that are registered ThreadingModel=Free or  ThreadingModel=Both.


Explain the differences between Server-side and Client-side code? Server side scripting means that all the script will be executed by the server and  interpreted as needed. ASP doesn’t have some of the functionality like sockets, uploading,  etc. For these you have to make a custom components usually in VB or VC++. Client side  scripting means that the script will be executed immediately in the browser such as form field validation, clock, email validation, etc. Client side scripting is usually done in  VBScript or JavaScript. Download time, browser compatibility, and visible code – since  JavaScript and VBScript code is included in the HTML page, then anyone can see the code by viewing the page source. Also a possible security hazards for the client computer.

 
What type of code (server or client) is found in a Code-Behind class?
C#


Should validation (did the user enter a real date) occur server-side or client-side? Why?Client-side validation because there is no need to request a server side date when you  could obtain a date from the client machine.

What are ASP.NET Web Forms? How is this technology different than what is available though ASP?
Web Forms are the heart and soul of ASP.NET. Web Forms are the User Interface (UI) elements that give your Web applications their look and feel. Web Forms are similar to Windows Forms in that they provide properties, methods, and events for the controls that are placed onto  them. However, these UI elements render themselves in the appropriate markup language   required by the request, e.g. HTML. If you use Microsoft Visual Studio .NET, you will also get the familiar drag-and-drop interface used to create your UI for your Web application.

 
What is the difference between Server.Transfer and Response.Redirect? Why would I choose one over the other?
In earlier versions of IIS, if we wanted to send a user to a new Web page, the only option we had was Response.Redirect. While this method does accomplish our goal, it has several important drawbacks. The biggest problem is that this method causes each page to be treated as a separate transaction. Besides making it difficult to maintain your transactional   integrity, Response.Redirect introduces some additional headaches. First, it prevents good encapsulation of code. Second, you lose access to all of the properties in the Request  object. Sure, there are workarounds, but they’re difficult. Finally, Response.Redirect  necessitates a round trip to the client, which, on high-volume sites, causes scalability problems.
As you might suspect, Server.Transfer fixes all of these problems. It does this by performing the transfer on the server without requiring a roundtrip to the client.


How can you provide an alternating color scheme in a Repeater control?
AlternatingItemTemplate Like the ItemTemplate element, but rendered for every other row (alternating items) in the Repeater control. You can specify a different appearance for the AlternatingItemTemplate element by setting its style properties.

 
Which template must you provide, in order to display data in a Repeater control?
ItemTemplate


What event handlers can I include in Global.asax?

Application_Start,Application_End, Application_AcquireRequestState, Application_AuthenticateRequest, Application_AuthorizeRequest, Application_BeginRequest, Application_Disposed,  Application_EndRequest, Application_Error, Application_PostRequestHandlerExecute, Application_PreRequestHandlerExecute,
Application_PreSendRequestContent, Application_PreSendRequestHeaders, Application_ReleaseRequestState, Application_ResolveRequestCache, Application_UpdateRequestCache, Session_Start,Session_End
You can optionally include “On” in any of method names. For example, you can name a BeginRequest event handler.Application_BeginRequest or Application_OnBeginRequest.You can also include event handlers in Global.asax for events fired by custom HTTP modules.Note that not all of the event handlers make sense for Web Services (they’re designed for ASP.NET applications in general, whereas .NET XML Web Services are specialized instances of an ASP.NET app). For example, the Application_AuthenticateRequest and Application_AuthorizeRequest events are designed to be used with ASP.NET Forms authentication.
 
What is different b/w  webconfig.xml & Machineconfig.xml
Web.config & machine.config both are configuration files.Web.config contains settings specific to an application where as machine.config contains settings to a computer. The Configuration system first searches settings in machine.config file & then looks in application configuration  files.Web.config, can appear in multiple directories on an ASP.NET Web application server. Each Web.config file applies configuration settings to its own directory and all child directories below it. There is only Machine.config file on a web server.
If I’m developing an application that must accomodate multiple security levels though secure login and my ASP.NET web appplication is spanned across three web-servers (using round-robbin load balancing) what would be the best approach to maintain login-in state for the users?
Use the state server or store the state in the database. This can be easily done through simple setting change in the web.config.
<SESSIONSTATE
StateConnectionString="tcpip=127.0.0.1:42424"
sqlConnectionString="data source=127.0.0.1; user id=sa; password="
cookieless="false"
timeout="30"
/>
You can specify mode as “stateserver” or “sqlserver”.
Where would you use an iHTTPModule, and what are the limitations of any approach you might take in implementing one
“One of ASP.NET’s most useful features is the extensibility of the HTTP pipeline, the path that data takes between client and server. You can use them to extend your ASP.NET applications by adding pre- and post-processing to each HTTP request coming into your application. For example, if you wanted custom authentication facilities for your application, the best technique would be to intercept the request when it comes in and process the request in a custom HTTP module.
 
How do you turn off cookies for one page in your site?
Since no Page Level directive is present, I am afraid that cant be done.


How do you create a permanent cookie? Permanent cookies are available until a specified expiration date, and are stored on the hard disk.So Set the ‘Expires’ property any value greater than DataTime.MinValue with respect to the current datetime. If u want the cookie which never expires set its Expires property equal to DateTime.maxValue.
Which method do you use to redirect the user to another page without performing a round trip to the client?
Server.Transfer and Server.Execute

 
What property do you have to set to tell the grid which page to go to when using the Pager object?
CurrentPageIndex


Should validation (did the user enter a real date) occur server-side or client-side? Why? It should occur both at client-side and Server side.By using expression validator control with the specified expression ie.. the regular expression provides the facility of only validatating the date specified is in the correct format or not. But for checking the date where it is the real data or not should be done at the server side, by getting the system date ranges and checking the date whether it is in between that range or not.

 
What does the “EnableViewState” property do? Why would I want it on or off? 
Enable ViewState turns on the automatic state management feature that enables server controls to re-populate their values on a round trip without requiring you to write any code. This feature is not free however, since the state of a control is passed to and from the server in a hidden form field. You should be aware of when ViewState is helping you and when it is not. For example, if you are binding a control to data on every round trip, then you do not need the control to maintain it’s view state, since you will wipe out any re-populated data in any case. ViewState is enabled for all server controls by default. To disable it, set the EnableViewState property of the control to false.


What is the difference between Server.Transfer and Response.Redirect? Why would I choose one over the other? 
Server.Transfer() : client is shown as it is on the requesting page only, but the all the content is of the requested page. Data can be persist accros the pages using Context.Item collection, which is one of the best way to transfer data from one page to another keeping the page state alive.

Response.Redirect() :client know the physical location (page name and query string as well). Context.Items loses the persisitance when nevigate to destination page. In earlier versions of IIS, if we wanted to send a user to a new Web page, the only option we had was Response.Redirect. While this method does accomplish our goal, it has several important drawbacks. The biggest problem is that this method causes each page to be treated as a separate transaction. Besides making it difficult to maintain your transactional integrity, Response.Redirect introduces some additional headaches. First, it prevents good encapsulation of code. Second, you lose access to all of the properties in the Request object. Sure, there are workarounds, but they’re difficult. Finally, Response.Redirect necessitates a round trip to the client, which, on high-volume sites, causes scalability problems. As you might suspect, Server.Transfer fixes all of these problems. It does this by performing the transfer on the server without requiring a roundtrip to the client.


Can you give an example of when it would be appropriate to use a web service as opposed to a non-serviced .NET component? 

  • Communicating through a Firewall When building a distributed application with 100s/1000s of users spread over multiple locations, there is always the problem of communicating between client and server because of firewalls and proxy servers. Exposing your middle tier components as Web Services and invoking the directly from a Windows UI is a very valid option.
  • Application Integration When integrating applications written in various languages and running on disparate systems. Or even applications running on the same platform that have been written by separate vendors.
  • Business-to-Business Integration This is an enabler for B2B intergtation which allows one to expose vital business processes to authorized supplier and customers. An example would be exposing electronic ordering and invoicing, allowing customers to send you purchase orders and suppliers to send you invoices electronically.
  • Software Reuse This takes place at multiple levels. Code Reuse at the Source code level or binary componet-based resuse. The limiting factor here is that you can reuse the code but not the data behind it. Webservice overcome this limitation. A scenario could be when you are building an app that aggregates the functionality of serveral other Applicatons. Each of these functions could be performed by individual apps, but there is value in perhaps combining the the multiple apps to present a unifiend view in a Portal or Intranet.
  • When not to use Web Services: Single machine Applicatons When the apps are running on the same machine and need to communicate with each other use a native API. You also have the options of using component technologies such as COM or .NET Componets as there is very little overhead.
  • Homogeneous Applications on a LAN If you have Win32 or Winforms apps that want to communicate to their server counterpart. It is much more efficient to use DCOM in the case of Win32 apps and .NET Remoting in the case of .NET Apps
Can you give an example of what might be best suited to place in the Application_Start and Session_Start subroutines? The Application_Start event is guaranteed to occur only once throughout the lifetime of the application. It’s a good place to initialize global variables. For example, you might want to retrieve a list of products from a database table and place the list in application state or the Cache object. SessionStateModule exposes both Session_Start and Session_End events.


What are the advantages and  disadvantages of viewstate?The primary advantages of the ViewState feature in ASP.NET are:

  1. Simplicity. There is no need to write possibly complex code to store form data between page submissions.
  2. Flexibility. It is possible to enable, configure, and disable ViewState on a control-by-control basis, choosing to persist the values of some fields but not others.
There are, however a few disadvantages that are worth pointing out:
  1. Does not track across pages. ViewState information does not automatically transfer from page to page. With the session approach, values can be stored in the session and accessed from other pages. This is not possible with ViewState, so storing data into the session must be done explicitly.
  2. ViewState is not suitable for transferring data for back-end systems. That is, data still has to be transferred to the back end using some form of data object.

Describe session handling in a webfarm, how does it work and what are the limits? ASP.NET Session supports storing of session data in 3 ways, i] in In-Process ( in the same memory that ASP.NET uses) , ii] out-of-process using Windows NT Service )in separate memory from ASP.NET ) or iii] in SQL Server (persistent storage). Both the Windows Service and SQL Server solution support a webfarm scenario where all the web-servers can be configured to share common session state store.

1. Windows Service :
We can start this service by Start | Control Panel | Administrative Tools | Services | . In that we service names  ASP.NET State Service. We can start or stop service by manually or configure to start automatically. Then we have to configure our web.config file

<CONFIGURATION><configuration>
<system.web>
<SessionState
mode = “StateServer”
stateConnectionString = “tcpip=127.0.0.1:42424”
stateNetworkTimeout = “10”
sqlConnectionString=”data source = 127.0.0.1; uid=sa;pwd=”
cookieless =”Flase”
timeout= “20” />
</system.web>
</configuration> </SYSTEM.WEB>
</CONFIGURATION>


Here ASP.Net Session is directed to use Windows Service for state management on local server (address : 127.0.0.1 is TCP/IP loop-back address). The default port is 42424. we can configure to any port but for that we have to manually edit the registry.
 Follow these simple steps

  • In a webfarm make sure you have the same config file in all your web servers.
  • Also make sure your objects are serializable.
  • For session state to be maintained across different web servers in the webfarm, the application path of the web-site in the IIS Metabase should be identical in all the web-servers in the webfarm.

Which template must you provide, in order to display data in a Repeater control? You have to use the ItemTemplate to Display data. Syntax is as follows,

< ItemTemplate >
< div class =”rItem” >
< img src=”images/<%# Container.DataItem(“ImageURL”)%>”  hspace=”10” />
< b > <% # Container.DataItem(“Title”)%>
< /div >
< ItemTemplate >
How can you provide an alternating color scheme in a Repeater control? 
Using the AlternatintItemTemplate


What property must you set, and what method must you call in your code, in order to bind the data from some data source to the Repeater control?
 Set the DataMember property to the name of the table to bind to. (If this property is not set, by default the first table in the dataset is used.)
DataBind method, use this method to bind data from a source to a server control. This method is commonly used after retrieving a data set through a database query.

What method do you use to explicitly kill a user s session?You can dump (Kill) the session yourself by calling the method Session.Abandon.

ASP.NET automatically deletes a user’s Session object, dumping its contents, after it has been idle for a configurable timeout interval. This interval, in minutes, is set in the section of the web.config file. The default is 20 minutes.
 
How do you turn off cookies for one page in your site? 
Use Cookie.Discard property, Gets or sets the discard flag set by the server. When true, this property instructs the client application not to save the Cookie on the user’s hard disk when a session ends.


Which two properties are on every validation control? We have two common properties for every validation controls

  1. Control to Validate,
  2. Error Message.
What tags do you need to add within the asp:datagrid tags to bind columns manually?
< asp:DataGrid id="dgCart" AutoGenerateColumns="False" CellPadding="4" Width="448px" runat="server"  >
< Columns >
< asp:ButtonColumn HeaderText="SELECT" Text="SELECT" CommandName="select" >< /asp:ButtonColumn >
< asp:BoundColumn DataField="ProductId" HeaderText="Product ID" >< /asp:BoundColumn >
< asp:BoundColumn DataField="ProductName" HeaderText="Product Name" >< /asp:BoundColumn >
< asp:BoundColumn DataField="UnitPrice" HeaderText="UnitPrice" >< /asp:BoundColumn >
< /Columns >
< /asp:DataGrid >
 
How do you create a permanent cookie? 
Permanent cookies are the ones that are most useful. Permanent cookies are available until a specified expiration date, and are stored on the hard disk. The location of cookies differs with each browser, but this doesn’t matter, as this is all handled by your browser and the server. If you want to create a permanent cookie called Name with a value of Nigel, which expires in one month, you’d use the following code
Response.Cookies ("Name") = "Nigel"
Response.Cookies ("Name"). Expires = DateAdd ("m", 1, Now ())


What tag do you use to add a hyperlink column to the DataGrid?

< asp:HyperLinkColumn > </ asp:HyperLinkColumn>


Which method do you use to redirect the user to another page without performing a round trip to the client?

Server.transfer
 
What is the transport protocol you use to call a Web service SOAP ?
HTTP Protocol
 
Explain role based security ?
Role Based Security lets you identify groups of users to allow or deny based on their role in the organization.In Windows NT and Windows XP, roles map to names used to identify user groups. Windows defines several built-in groups, including Administrators, Users, and Guests.To allow or deny access to certain groups of users, add the element to the authorization list in your Web application’s Web.config file.e.g.
<AUTHORIZATION>< authorization >
< allow roles="Domain Name\Administrators" / >   < !-- Allow Administrators in domain. -- >
< deny users="*"  / >                            < !-- Deny anyone else. -- >
< /authorization >
 
How do you register JavaScript for webcontrols ?
You can register javascript for controls using Attribtues.Add(scriptname,scripttext) method.
 
When do you set “” ?
Identity is a webconfig declaration under System.web, which helps to control the application Identity of the web applicaton. Which can be at any level(Machine,Site,application,subdirectory,or page), attribute impersonate with “true” as value specifies that client impersonation is used.


What are different templates available in Repeater,DataList and Datagrid ?

Templates enable one to apply complicated formatting to each of the items displayed by a control.Repeater control supports five types of templates.HeaderTemplate controls  how the header of the repeater control is formatted.ItemTemplate controls the formatting of each  item displayed.AlternatingItemTemplate controls how alternate items are formatted and the  SeparatorTemplate displays a separator between each item displyed.FooterTemplate is used for  controlling how the footer of the repeater control is formatted.The DataList and Datagrid supports two templates in addition to the above five.SelectedItem Template controls how a selected item is  formatted and EditItemTemplate controls how an item selected for editing is formatted.
 
What is ViewState ? and how it is managed ?
ASP.NET ViewState is a new kind of state service that developers can use to track  UI state on a per-user basis. Internally it uses an an old Web programming trick-roundtripping  state in a hidden form field and bakes it right into the page-processing framework.It needs less code to write and maintain state in your Web-based forms.
 
What is web.config file ?
Web.config file is the configuration file for the Asp.net web application. There is one web.config  file for one asp.net application which configures
the particular application. Web.config file is  written in XML with specific tags having specific meanings.It includes databa which includes
connections,Session States,Error Handling,Security etc.
For example :
< configuration >
< appSettings >
< add key="ConnectionString"
value="server=localhost;uid=sa;pwd=;database=MyDB" / >
< /appSettings >
< /configuration >
 
What is advantage of viewstate and what are benefits?
When a form is submitted in classic ASP, all form values are cleared. Suppose you have submitted a  form with a lot of information and the server comes back with an error. You will have to go back to  the form and correct the information. You click the back button, and what happens…….ALL form values are CLEARED, and you will have to start all over again! The site did not maintain your  ViewState.With ASP .NET, the form reappears in the browser window together with all form  values.This is because ASP .NET maintains your ViewState. The ViewState indicates the status of the  page when submitted to the server.
 
What tags do you need to add within the asp:datagrid tags to bind columns manually?
Set AutoGenerateColumns Property to false on the datagrid tag and then use Column tag and an ASP:databound tag
< asp:DataGrid runat="server" id="ManualColumnBinding" AutoGenerateColumns="False" >
< Columns >
< asp:BoundColumn HeaderText="Column1" DataField="Column1"/ >
< asp:BoundColumn HeaderText="Column2" DataField="Column2"/ >
< /Columns >
< /asp:DataGrid >
<asp:DataGrid id=ManualColumnBinding runat="server" AutoGenerateColumns="False">
<COLUMNS>   <asp:BoundColumn HeaderText="Column2" DataField="Column2"></asp:BoundColumn>
</asp:DataGrid>
 
Which property on a Combo Box do you set with a column name, prior to setting the DataSource, to display data in the combo box? 
DataTextField and  DataValueField


Which control would you use if you needed to make sure the values in two different controls matched?

CompareValidator is used to ensure that two fields are identical.
 
What is validationsummary server control?where it is used?.
The ValidationSummary control allows you to summarize the error messages from all validation controls on a Web page in a single location. The summary can be displayed as a list, a bulleted list, or a single paragraph, based on the value of the DisplayMode property. The error message displayed in the ValidationSummary control for each validation control on the page is specified by the ErrorMessage property of each validation control. If the ErrorMessage property of the validation control is not set, no error message is displayed in the ValidationSummary control for that validation control. You can also specify a custom title in the heading section of the ValidationSummary control by setting the HeaderText property.
You can control whether the ValidationSummary control is displayed or hidden by setting the ShowSummary property. The summary can also be displayed in a message box by setting the ShowMessageBox property to true.


What is the sequence of operation takes place when a page is loaded?BeginTranaction  – only if the request is transacted
Init    – every time a page is processed
LoadViewState  – Only on postback
ProcessPostData1  – Only on postback
Load    – every time
ProcessData2   – Only on Postback
RaiseChangedEvent  – Only on Postback
RaisePostBackEvent  – Only on Postback
PreRender   – everytime
BuildTraceTree  – only if tracing is enabled
SaveViewState  – every time
Render   – Everytime
End Transaction  – only if the request is transacted
Trace.EndRequest  – only when tracing is enabled
UnloadRecursive  – Every request

 
Difference between asp and asp.net?.
“ASP (Active Server Pages) and ASP.NET are both server side technologies for building web sites and web applications, ASP.NET is Managed compiled code – asp is interpreted. and ASP.net is fully Object oriented. ASP.NET has been entirely re-architected to provide a highly productive programming experience based on the .NET Framework, and a robust infrastructure for building reliable and scalable web
applications.”


Name the validation control available in asp.net?.RequiredField, RangeValidator,RegularExpression,Custom validator,compare Validator

What are the various ways of securing a web site that could prevent from hacking etc .. ?

  1. Authentication/Authorization
  2. Encryption/Decryption
  3. Maintaining web servers outside the corporate firewall. etc.,
What is the difference between in-proc and out-of-proc? 
An inproc is one which runs in the same process area as that of the client giving tha advantage of speed but the disadvantage of stability becoz if it crashes it takes the client application also with it.Outproc is one which works outside the clients memory thus giving stability to the client, but we have to compromise a bit on speed.
 
When you’re running a component within ASP.NET, what process is it running within on Windows XP? Windows 2000? Windows 2003?
On Windows 2003 (IIS 6.0) running in native mode, the component is running within the w3wp.exe process associated with the application pool which has been configured for the web application containing the component.
On Windows 2003 in IIS 5.0 emulation mode, 2000, or XP, it’s running within the IIS helper process whose name I do not remember, it being quite a while since I last used IIS 5.0.
 
What does aspnet_regiis -i do ?

Aspnet_regiis.exe is The ASP.NET IIS Registration tool allows an administrator or installation program to easily update the script maps for an ASP.NET application to point to the ASP.NET ISAPI version associated with the tool. The tool can also be used to display the status of all installed versions of ASP. NET, register the ASP.NET version coupled with the tool, create client-script directories, and perform other configuration operations.

When multiple versions of the .NET Framework are executing side-by-side on a single computer, the ASP.NET ISAPI version mapped to an ASP.NET application determines which version of the common language runtime is used for the application.

The tool can be launched with a set of optional parameters. Option “i” Installs the version of ASP.NET associated with Aspnet_regiis.exe and updates the script maps at the IIS metabase root and below. Note that only applications that are currently mapped to an earlier version of ASP.NET are affected

 
What is a PostBack? 
The process in which a Web page sends data back to the same page on the server.


What is ViewState? How is it encoded? Is it encrypted? Who uses ViewState? ViewState is the mechanism ASP.NET uses to keep track of server control state values that don’t otherwise post back as part of the HTTP form. ViewState Maintains the UI State of a Page
  ViewState is base64-encoded. 
 It is not encrypted but it can be encrypted by setting EnableViewStatMAC=”true” & setting the machineKey validation type to 3DES.  If you want to NOT maintain the ViewState, include the directive at the top of an .aspx page or add the attribute EnableViewState=”false” to any control.\

 
What is the element and what two ASP.NET technologies is it used for?
Configures keys to use for encryption and decryption of forms authentication cookie data and view state data, and for verification of out-of-process session state identification.There fore 2 ASP.NET technique in which it is used are Encryption/Decryption & Verification
 
What three Session State providers are available in ASP.NET 1.1? What are the pros and cons of each?
ASP.NET provides three distinct ways to store session data for your application: in-process session state, out-of-process session state as a Windows service, and out-of-process session state in a SQL Server database. Each has it advantages.
  1. In-process session-state mode
    Limitations:
    * When using the in-process session-state mode, session-state data is lost if aspnet_wp.exe or the application domain restarts.
    * If you enable Web garden mode in the element of the application’s Web.config file, do not use in-process session-state mode. Otherwise, random data loss can occur.
    Advantage:
    * in-process session state is by far the fastest solution. If you are storing only small amounts of volatile data in session state, it is recommended that you use the in-process provider.
  2. The State Server simply stores session state in memory when in out-of-proc mode. In this mode the worker process talks directly to the State Server
  3. SQL mode, session states are stored in a SQL Server database and the worker process talks directly to SQL. The ASP.NET worker processes are then able to take advantage of this simple storage service by serializing and saving (using .NET serialization services) all objects within a client’s Session collection at the end of each Web request
    Both these out-of-process solutions are useful primarily if you scale your application across multiple processors or multiple computers, or where data cannot be lost if a server or process is restarted.
What is the difference between HTTP-Post and HTTP-Get?
As their names imply, both HTTP GET and HTTP POST use HTTP as their underlying protocol. Both of these methods encode request parameters as name/value pairs in the HTTP request.
The GET method creates a query string and appends it to the script’s URL on the server that handles the request.
The POST method creates a name/value pairs that are passed in the body of the HTTP request message.
 
Name and describe some HTTP Status Codes and what they express to the requesting client.
When users try to access content on a server that is running Internet Information Services (IIS) through HTTP or File Transfer Protocol (FTP), IIS returns a numeric code that indicates the status of the request. This status code is recorded in the IIS log, and it may also be displayed in the Web browser or FTP client. The status code can indicate whether a particular request is successful or unsuccessful and can also reveal the exact reason why a request is unsuccessful. There are 5 groups ranging from 1xx – 5xx of http status codes exists.
101 – Switching protocols.
200 – OK. The client request has succeeded
302 – Object moved.
400 – Bad request.
500.13 – Web server is too busy.
 
Explain and the usage of VaryByParam, VaryByHeader.
OutputCache is used to control the caching policies of an ASP.NET page or user control. To cache a page @OutputCache directive should be defined as follows
VaryByParam: A semicolon-separated list of strings used to vary the output cache. By default, these strings correspond to a query string value sent with GET method attributes, or a parameter sent using the POST method. When this attribute is set to multiple parameters, the output cache contains a different version of the requested document for each specified parameter. Possible values include none, *, and any valid query string or POST parameter name.
VaryByHeader: A semicolon-separated list of HTTP headers used to vary the output cache. When this attribute is set to multiple headers, the output cache contains a different version of the requested document for each specified header.
 
What is the difference between repeater over datalist and datagrid?
The Repeater class is not derived from the WebControl class, like the DataGrid and DataList. Therefore, the Repeater lacks the stylistic properties common to both the DataGrid and DataList. What this boils down to is that if you want to format the data displayed in the Repeater, you must do so in the HTML markup.
The Repeater control provides the maximum amount of flexibility over the HTML produced. Whereas the DataGrid wraps the DataSource contents in an HTML
, and the DataList wraps the contents in either an HTMLor tags (depending on the DataList’s RepeatLayout property), the Repeater adds absolutely no HTML content other than what you explicitly specify in the templates.While using Repeater control, If we wanted to display the employee names in a bold font we’d have to alter the “ItemTemplate” to include an HTML bold tag, Whereas with the DataGrid or DataList, we could have made the text appear in a bold font by setting the control’s ItemStyle-Font-Bold property to True.The Repeater’s lack of stylistic properties can drastically add to the development time metric. For example, imagine that you decide to use the Repeater to display data that needs to be bold, centered, and displayed in a particular font-face with a particular background color. While all this can be specified using a few HTML tags, these tags will quickly clutter the Repeater’s templates. Such clutter makes it much harder to change the look at a later date. Along with its increased development time, the Repeater also lacks any built-in functionality to assist in supporting paging, editing, or editing of data. Due to this lack of feature-support, the Repeater scores poorly on the usability scale.
However, The Repeater’s performance is slightly better than that of the DataList’s, and is more noticeably better than that of the DataGrid’s. Following figure shows the number of requests per second the Repeater could handle versus the DataGrid and DataList
 
Can we handle the error and redirect to some pages using web.config?
Yes, we can do this, but to handle errors, we must know the error codes; only then we can take the user to a proper error message page, else it may confuse the user.
CustomErrors Configuration section in web.config file:
The default configuration is:
< customErrors mode="RemoteOnly"
defaultRedirect="Customerror.aspx" >
< error statusCode="404" redirect="Notfound.aspx" / >
< /customErrors >
If mode is set to Off, custom error messages will be disabled. Users will receive detailed exception error messages.
If mode is set to On, custom error messages will be enabled.
If mode is set to RemoteOnly, then users will receive custom errors, but users accessing the site locally will receive detailed error messages.
Add an tag for each error you want to handle. The error tag will redirect the user to the Notfound.aspx page when the site returns the 404 (Page not found) error.
[Example]
There is a page MainForm.aspx
Private
Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs)
Handles MyBase.Load
'Put user code to initialize the
page here
Dim str As System.Text.StringBuilder
str.Append("hi") ' Error Line as str is not instantiated
Response.Write(str.ToString)
End Sub
[Web.Config]
‘ a simple redirect will take the user to Error.aspx [user defined] error file.
< customErrors mode="RemoteOnly" defaultRedirect="Customerror.aspx" >
< error statusCode="404" redirect="Notfound.aspx" / >
< /customErrors >
'This will take the user to NotFound.aspx defined in IIS.
 
How do you implement Paging in .Net?
The DataGrid provides the means to display a group of records from the data source (for example, the first 10), and then navigate to the “page” containing the next 10 records, and so on through the data.
Using Ado.Net we can explicit control over the number of records returned from the data source, as well as how much data is to be cached locally in the DataSet.
  1. Using DataAdapter.fill method give the value of ‘Maxrecords’ parameter
    (Note: – Don’t use it because query will return all records but fill the dataset based on value of ‘maxrecords’ parameter).
  2. For SQL server database, combines a WHERE clause and a ORDER BY clause with TOP predicate.
  3. If Data does not change often just cache records locally in DataSet and just take some records from the DataSet to display.
What is the difference between Server.Transfer and Response.Redirect?
Server.Transfer() : client is shown as it is on the requesting page only, but the all the content is of the requested page. Data can be persist across the pages using Context.Item collection, which is one of the best way to transfer data from one page to another keeping the page state alive.
Response.Dedirect() :client knows the physical location (page name and query string as well). Context.Items loses the persistence when navigate to destination page. In earlier versions of IIS, if we wanted to send a user to a new Web page, the only option we had was Response.Redirect. While this method does accomplish our goal, it has several important drawbacks. The biggest problem is that this method causes each page to be treated as a separate transaction. Besides making it difficult to maintain your transactional integrity, Response.Redirect introduces some additional headaches. First, it prevents good encapsulation of code. Second, you lose access to all of the properties in the Request object. Sure, there are workarounds, but they’re difficult. Finally, Response.Redirect necessitates a round trip to the client, which, on high-volume sites, causes scalability problems. As you might suspect, Server.Transfer fixes all of these problems. It does this by performing the transfer on the server without requiring a roundtrip to the client.
Response.Redirect sends a response to the client browser instructing it to request the second page. This requires a round-trip to the client, and the client initiates the Request for the second page. Server.Transfer transfers the process to the second page without making a round-trip to the client. It also transfers the HttpContext to the second page, enabling the second page access to all the values in the HttpContext of the first page.
 
Can you create an app domain?
Yes, We can create user app domain by calling on of the following overload static methods of the System.AppDomain class
  1. Public static AppDomain CreateDomain(String friendlyName)
  2. Public static AppDomain CreateDomain(String friendlyName, Evidence securityInfo)
  3. Public static AppDomain CreateDomain(String friendlyName, Evidence securityInfo, AppDomainSetup info)
  4. Public static AppDomain CreateDomain(String friendlyName, Evidence securityInfo, String appBasePath, String appRelativeSearchPath, bool shadowCopyFiles)
What are the various security methods which IIS Provides apart from .NET ?
The various security methods which IIS provides are
  1. Authentication Modes
  2. IP Address and Domain Name Restriction
  3. DNS Lookups DNS Lookups
  4. The Network ID and Subnet Mask
  5. SSL
What is Web Gardening? How would using it affect a design?  
The Web Garden Model
The Web garden model is configurable through the section of the machine.config file. Notice that the section is the only configuration section that cannot be placed in an application-specific web.config file. This means that the Web garden mode applies to all applications running on the machine. However, by using the node in the machine.config source, you can adapt machine-wide settings on a per-application basis.
Two attributes in the section affect the Web garden model. They are webGarden and cpuMask. The webGarden attribute takes a Boolean value that indicates whether or not multiple worker processes (one per each affinitized CPU) have to be used. The attribute is set to false by default. The cpuMask attribute stores a DWORD value whose binary representation provides a bit mask for the CPUs that are eligible to run the ASP.NET worker process. The default value is -1 (0xFFFFFF), which means that all available CPUs can be used. The contents of the cpuMask attribute is ignored when the webGarden attribute is false. The cpuMask attribute also sets an upper bound to the number of copies of aspnet_wp.exe that are running.
Web gardening enables multiple worker processes to run at the same time. However, you should note that all processes will have their own copy of application state, in-process session state, ASP.NET cache, static data, and all that is needed to run applications. When the Web garden mode is enabled, the ASP.NET ISAPI launches as many worker processes as there are CPUs, each a full clone of the next (and each affinitized with the corresponding CPU). To balance the workload, incoming requests are partitioned among running processes in a round-robin manner. Worker processes get recycled as in the single processor case. Note that ASP.NET inherits any CPU usage restriction from the operating system and doesn’t include any custom semantics for doing this.
All in all, the Web garden model is not necessarily a big win for all applications. The more stateful applications are, the more they risk to pay in terms of real performance. Working data is stored in blocks of shared memory so that any changes entered by a process are immediately visible to others. However, for the time it takes to service a request, working data is copied in the context of the process. Each worker process, therefore, will handle its own copy of working data, and the more stateful the application, the higher the cost in performance. In this context, careful and savvy application benchmarking is an absolute must.
Changes made to the section of the configuration file are effective only after IIS is restarted. In IIS 6, Web gardening parameters are stored in the IIS metabase; the webGarden and cpuMask attributes are ignored.
 
What is view state?.where it stored?.can we disable it?
The web is state-less protocol, so the page gets instantiated, executed, rendered and then disposed on every round trip to the server. The developers code to add “statefulness” to the page by using Server-side storage for the state or posting the page to itself. When require to persist and read the data in control on webform, developer had to read the values and store them in hidden variable (in the form), which were then used to restore the values. With advent of .NET framework, ASP.NET came up with ViewState mechanism, which tracks the data values of server controls on ASP.NET webform. In effect,ViewState can be viewed as “hidden variable managed by ASP.NET framework!”. When ASP.NET page is executed, data values from all server controls on page are collected and encoded as single string, which then assigned to page’s hidden atrribute  “”, that is part of page sent to the client.
ViewState value is temporarily saved in the client’s browser.ViewState can be disabled for a single control, for an entire page orfor an entire web application. The syntax is:
Disable ViewState for control (Datagrid in this example)
< asp:datagrid EnableViewState="false" ... / >
Disable ViewState for a page, using Page directive
< %@ Page EnableViewState="False" ... % >
Disable ViewState for application through entry in web.config
< Pages EnableViewState="false" ... / >

.NET FrameWork FAQ’s

When was .NET announced?
Bill Gates delivered a keynote at Forum 2000, held June 22, 2000, outlining the .NET ‘vision’. The July 2000 PDC had a number of sessions on .NET technology, and delegates were given CDs containing a pre-release version of the .NET framework/SDK and Visual Studio.NET.
 
When was the first version of .NET released?
The final version of the 1.0 SDK and runtime was made publicly available around 6pm PST on 15-Jan-2002. At the same time, the final version of Visual Studio.NET was made available to MSDN subscribers.
 
What platforms does the .NET Framework run on?
The runtime supports Windows XP, Windows 2000, NT4 SP6a and Windows ME/98. Windows 95 is not supported. Some parts of the framework do not work on all platforms – for example, ASP.NET is only supported on Windows XP and Windows 2000. Windows 98/ME cannot be used for development.
IIS is not supported on Windows XP Home Edition, and so cannot be used to host ASP.NET. However, the ASP.NET Web Matrix
web server does run on XP Home.
The Mono project is attempting to implement the .NET framework on Linux.
 
What is the CLR?
CLR = Common Language Runtime. The CLR is a set of standard resources that (in theory) any .NET program can take advantage of, regardless of programming language. Robert Schmidt (Microsoft) lists the following CLR resources in his MSDN PDC# article:
Object-oriented programming model (inheritance, polymorphism, exception handling, garbage collection)
 Security model 
 Type system 
 All .NET base classes 
 Many .NET framework classes 
 Development, debugging, and profiling tools 
 Execution and code management 
 IL-to-native translators and optimizers 
What this means is that in the .NET world, different programming languages will be more equal in capability than they have ever been before, although clearly not all languages will support all CLR services.

What is the CTS?

CTS = Common Type System. This is the range of types that the .NET runtime understands, and therefore that .NET applications can use. However note that not all .NET languages will support all the types in the CTS. The CTS is a superset of the CLS.

What is the CLS?

CLS = Common Language Specification. This is a subset of the CTS which all .NET languages are expected to support. The idea is that any program which uses CLS-compliant types can interoperate with any .NET program written in any language.
In theory this allows very tight interop between different .NET languages – for example allowing a C# class to inherit from a VB class.

What is IL?

IL = Intermediate Language. Also known as MSIL (Microsoft Intermediate Language) or CIL (Common Intermediate Language). All .NET source code (of any language) is compiled to IL. The IL is then converted to machine code at the point where the software is installed, or at run-time by a Just-In-Time (JIT) compiler.

What does ‘managed’ mean in the .NET context?

The term ‘managed’ is the cause of much confusion. It is used in various places within .NET, meaning slightly different things.Managed code: The .NET framework provides several core run-time services to the programs that run within it – for example exception handling and security. For these services to work, the code must provide a minimum level of information to the runtime.
Such code is called managed code. All C# and Visual Basic.NET code is managed by default. VS7 C++ code is not managed by default, but the compiler can produce managed code by specifying a command-line switch (/com+).
Managed data: This is data that is allocated and de-allocated by the .NET runtime’s garbage collector. C# and VB.NET data is always managed. VS7 C++ data is unmanaged by default, even when using the /com+ switch, but it can be marked as managed using the __gc keyword.Managed classes: This is usually referred to in the context of Managed Extensions (ME) for C++. When using ME C++, a class can be marked with the __gc keyword. As the name suggests, this means that the memory for instances of the class is managed by the garbage collector, but it also means more than that. The class becomes a fully paid-up member of the .NET community with the benefits and restrictions that brings. An example of a benefit is proper interop with classes written in other languages – for example, a managed C++ class can inherit from a VB class. An example of a restriction is that a managed class can only inherit from one base class.

What is reflection?

All .NET compilers produce metadata about the types defined in the modules they produce. This metadata is packaged along with the module (modules in turn are packaged together in assemblies), and can be accessed by a mechanism called reflection. The System.Reflection namespace contains classes that can be used to interrogate the types for a module/assembly.
Using reflection to access .NET metadata is very similar to using ITypeLib/ITypeInfo to access type library data in COM, and it is used for similar purposes – e.g. determining data type sizes for marshaling data across context/process/machine boundaries.
Reflection can also be used to dynamically invoke methods (see System.Type.InvokeMember ) ,  or even create types dynamically at run-time (see System.Reflection.Emit.TypeBuilder).
What is the difference between Finalize and Dispose (Garbage collection) ?
Class instances often encapsulate control over resources that are not managed by the runtime, such as window handles (HWND), database connections, and so on. Therefore, you should provide both an explicit and an implicit way to free those resources. Provide implicit control by implementing the protected Finalize Method on an object (destructor syntax in C# and the Managed Extensions for C++). The garbage collector calls this method at some point after there are no longer any valid references to the object. In some cases, you might want to provide programmers using an object with the ability to explicitly release these external resources before the garbage collector frees the object. If an external resource is scarce or expensive, better performance can be achieved if the programmer explicitly releases resources when they are no longer being used. To provide explicit control, implement the Dispose method provided by the IDisposable Interface. The consumer of the object should call this method when it is done using the object.
Dispose can be called even if other references to the object are alive. Note that even when you provide explicit control by way of Dispose, you should provide implicit cleanup using the Finalize method. Finalize provides a backup to prevent resources from permanently leaking if the programmer fails to call Dispose.
What is Partial Assembly References?
Full Assembly reference: A full assembly reference includes the assembly’s text name, version, culture, and public key token (if the assembly has a strong name). A full assembly reference is required if you reference any assembly that is part of the common
language runtime or any assembly located in the global assembly cache.
Partial Assembly reference: We can dynamically reference an assembly by providing only partial information, such as specifying only the assembly name. When you specify a partial assembly reference, the runtime looks for the assembly only in the application
directory.
We can make partial references to an assembly in your code one of the following ways:
-> Use a method such as System.Reflection.Assembly.Load and specify only a partial reference. The runtime checks for the assembly in the application directory.
-> Use the System.Reflection.Assembly.LoadWithPartialName method and specify only a partial reference. The runtime checks for the assembly in the application directory and in the global assembly cache

Changes to which portion of version number indicates an incompatible change?Major or minor. Changes to the major or minor portion of the version number indicate an incompatible change. Under this convention then, version 2.0.0.0 would be considered incompatible with version 1.0.0.0. Examples of an incompatible change would be a change to the types of some method parameters or the removal of a type or method altogether. Build. The Build number is typically used to distinguish between daily builds or smaller compatible releases. Revision. Changes to the revision number are typically reserved for an incremental build needed to fix a particular bug. You’ll sometimes hear this referred to as the “emergency bug fix” number in that the revision is what is often changed when a fix to a specific bug is shipped to a customer.

 
What is side-by-side execution? Can two application one using private assembly and other using Shared assembly be stated as a side-by-side executables?
Side-by-side execution is the ability to run multiple versions of an application or component on the same computer. You can have multiple versions of the common language runtime, and multiple versions of applications and components that use a version of the runtime, on the same computer at the same time. Since versioning is only applied to shared assemblies, and not to private assemblies, two application one using private assembly and one using shared assembly cannot be stated as side-by-side executables.

Why string are called Immutable data Type ?

The memory representation of string is an Array of Characters, So on re-assigning the new array of Char is formed & the start address is changed . Thus keeping the Old string in Memory for Garbage Collector to be disposed.
What does assert() method do?
In debug compilation, assert takes in a Boolean condition as a parameter, and shows the error dialog if the condition is false. The program proceeds without any interruption if the condition is true.

What’s the difference between the Debug class and Trace class?

Documentation looks the same.  Use Debug class for debug builds, use Trace class for both debug and release builds.
Why are there five tracing levels in System.Diagnostics.TraceSwitcher?
The tracing dumps can be quite verbose.  For applications that are constantly running you run the risk of overloading the machine and the hard drive.  Five levels range from None to Verbose, allowing you to fine-tune the tracing activities.

Where is the output of TextWriterTraceListener redirected?

To the Console or a text file depending on the parameter passed to the constructor.
How do assemblies find each other?
By searching directory paths. There are several factors which can affect the path (such as the AppDomain host, and application configuration files), but for private assemblies the search path is normally the application’s directory and its sub-directories. For shared assemblies, the search path is normally same as the private assembly path plus the shared assembly cache.

How does assembly versioning work?

Each assembly has a version number called the compatibility version. Also each reference to an assembly (from another assembly) includes both the name and version of the referenced assembly.The version number has four numeric parts (e.g. 5.5.2.33). Assemblies with either of the first two parts different are normally viewed as incompatible. If the first two parts are the same, but the third is different, the assemblies are deemed as ‘maybe compatible’. If only the fourth part is different, the assemblies are deemed compatible. However, this is just the default guideline – it is the version policy that decides to what extent these rules are enforced. The version policy can be specified via the application configuration file.
What is garbage collection?
Garbage collection is a system whereby a run-time component takes responsibility for managing the lifetime of objects and the heap memory that they occupy. This concept is not new to .NET – Java and many other languages/runtimes have used garbage collection for some time.

Why doesn’t the .NET runtime offer deterministic destruction?

Because of the garbage collection algorithm. The .NET garbage collector works by periodically running through a list of all the objects that are currently being referenced by an application. All the objects that it doesn’t find during this search are ready to be destroyed and the memory reclaimed. The implication of this algorithm is that the runtime doesn’t get notified immediately when the final reference on an object goes away – it only finds out during the next sweep of the heap.
Futhermore, this type of algorithm works best by performing the garbage collection sweep as rarely as possible. Normally heap exhaustion is the trigger for a collection sweep.

Is the lack of deterministic destruction in .NET a problem?

It’s certainly an issue that affects component design. If you have objects that maintain expensive or scarce resources (e.g. database locks), you need to provide some way for the client to tell the object to release the resource when it is done. Microsoft recommend that you provide a method called Dispose() for this purpose. However, this causes problems for distributed objects – in a distributed system who calls the Dispose() method? Some form of reference-counting or ownership-management mechanism is needed to handle distributed objects – unfortunately the runtime offers no help with this.

What is serialization?

Serialization is the process of converting an object into a stream of bytes. Deserialization is the opposite process of creating an object from a stream of bytes. Serialization / Deserialization is mostly used to transport objects (e.g. during remoting), or to persist
objects (e.g. to a file or database).

Does the .NET Framework have in-built support for serialization?

There are two separate mechanisms provided by the .NET class library – XmlSerializer and SoapFormatter/BinaryFormatter. Microsoft uses XmlSerializer for Web Services, and uses SoapFormatter/BinaryFormatter for remoting. Both are available for use in your own code.

Can I customise the serialization process?

Yes. XmlSerializer supports a range of attributes that can be used to configure serialization for a particular class. For example, a field or property can be marked with the [XmlIgnore] attribute to exclude it from serialization. Another example is the [XmlElement] attribute, which can be used to specify the XML element name to be used for a particular property or field.
Serialization via SoapFormatter/BinaryFormatter can also be controlled to some extent by attributes. For example, the [NonSerialized] attribute is the equivalent of XmlSerializer’s [XmlIgnore] attribute. Ultimate control of the serialization process can be acheived by implementing the the ISerializable interface on the class whose instances are to be serialized.

Why is XmlSerializer so slow?

There is a once-per-process-per-type overhead with XmlSerializer. So the first time you serialize or deserialize an object of a given type in an application, there is a significant delay. This normally doesn’t matter, but it may mean, for example, that XmlSerializer is a poor choice for loading configuration settings during startup of a GUI application.

Why do I get errors when I try to serialize a Hashtable?

XmlSerializer will refuse to serialize instances of any class that implements IDictionary, e.g. Hashtable. SoapFormatter and BinaryFormatter do not have this restriction.

What are attributes?

There are at least two types of .NET attribute. The first type I will refer to as a metadata attribute – it allows some data to be attached to a class or method. This data becomes part of the metadata for the class, and (like other class metadata) can be accessed via reflection.
The other type of attribute is a context attribute. Context attributes use a similar syntax to metadata attributes but they are fundamentally different. Context attributes provide an interception mechanism whereby instance activation and method calls can be pre- and/or post-processed.

How does CAS work?The CAS security policy revolves around two key concepts – code groups and permissions. Each .NET assembly is a member of a particular code group, and each code group is granted the permissions specified in a named permission set.
For example, using the default security policy, a control downloaded from a web site belongs to the ‘Zone – Internet’ code group, which adheres to the permissions defined by the ‘Internet’ named permission set. (Naturally the ‘Internet’ named permission set represents a very restrictive range of permissions.)

Who defines the CAS code groups?Microsoft defines some default ones, but you can modify these and even create your own. To see the code groups defined on your system, run ‘caspol -lg’ from the command-line. On my system it looks like this:
Level = Machine

Code Groups:
1.  All code: Nothing
1.1.  Zone – MyComputer: FullTrust
1.1.1.  Honor SkipVerification requests: SkipVerification
1.2.  Zone – Intranet: LocalIntranet
1.3.  Zone – Internet: Internet
1.4.  Zone – Untrusted: Nothing
1.5.  Zone – Trusted: Internet
1.6.  StrongName – 0024000004800000940000000602000000240000525341310004000003
000000CFCB3291AA715FE99D40D49040336F9056D7886FED46775BC7BB5430BA4444FEF8348EBD06
F962F39776AE4DC3B7B04A7FE6F49F25F740423EBF2C0B89698D8D08AC48D69CED0FC8F83B465E08
07AC11EC1DCC7D054E807A43336DDE408A5393A48556123272CEEEE72F1660B71927D38561AABF5C
AC1DF1734633C602F8F2D5:
Note the hierarchy of code groups – the top of the hierarchy is the most general (‘All code’), which is then sub-divided into several
groups, each of which in turn can be sub-divided. Also note that (somewhat counter-intuitively) a sub-group can be associated with a more permissive permission set than its parent.

How do I define my own code group?

Use caspol. For example, suppose you trust code from www.mydomain.com and you want it have full access to your system, but you want to keep the default restrictions for all other internet sites. To achieve this, you would add a new code group as a sub-group of the
‘Zone – Internet’ group, like this:
caspol -ag 1.3 -site www.mydomain.com FullTrust
Now if you run caspol -lg you will see that the new group has been added as group 1.3.1:
   1.3.  Zone – Internet: Internet
1.3.1.  Site – www.mydomain.com: FullTrust
Note that the numeric label (1.3.1) is just a caspol invention to make the code groups easy to manipulate from the command-line. The underlying runtime never sees it.
 
How do I change the permission set for a code group?
Use caspol. If you are the machine administrator, you can operate at the ‘machine’ level – which means not only that the changes you make become the default for the machine, but also that users cannot change the permissions to be more permissive. If you are a normal (non-admin) user you can still modify the permissions, but only to make them more restrictive. For example, to allow intranet code to do what it likes you might do this:
caspol -cg 1.2 FullTrust
Note that because this is more permissive than the default policy (on a standard system), you should only do this at the machine level – doing it at the user level will have no effect.

I can’t be bothered with all this CAS stuff. Can I turn it off?

Yes, as long as you are an administrator. Just run: caspol -s off
Can I look at the IL for an assembly?
Yes. MS supply a tool called Ildasm which can be used to view the metadata and IL for an assembly.

Can source code be reverse-engineered from IL?

Yes, it is often relatively straightforward to regenerate high-level source (e.g. C#) from IL.
How can I stop my code being reverse-engineered from IL?
There is currently no simple way to stop code being reverse-engineered from IL. In future it is likely that IL obfuscation tools will become available, either from MS or from third parties. These tools work by ‘optimising’ the IL in such a way that reverse-engineering becomes much more difficult.
Of course if you are writing web services then reverse-engineering is not a problem as clients do not have access to your IL.
Is there built-in support for tracing/logging?
Yes, in the System.Diagnostics namespace. There are two main classes that deal with tracing – Debug and Trace. They both work in a similar way – the difference is that tracing from the Debug class only works in builds that have the DEBUG symbol defined, whereas tracing from the Trace class only works in builds that have the TRACE symbol defined. Typically this means that you should use System.Diagnostics.Trace.WriteLine for tracing that you want to work in debug and release builds, and System.Diagnostics.Debug.WriteLine for tracing that you want to work only in debug builds.

Can I redirect tracing to a file?

Yes. The Debug and Trace classes both have a Listeners property, which is a collection of sinks that receive the tracing that you send via Debug.WriteLine and Trace.WriteLine respectively. By default the Listeners collection contains a single sink, which is an instance of the DefaultTraceListener class. This sends output to the Win32 OutputDebugString() function and also the System.Diagnostics.Debugger.Log() method. This is useful when debugging, but if you’re trying to trace a problem at a customer site, redirecting the output to a file is more appropriate. Fortunately, the TextWriterTraceListener class is provided for this purpose.

What are the contents of assembly?

In general, a static assembly can consist of four elements:
The assembly manifest, which contains assembly metadata. 
 Type metadata. 
 Microsoft intermediate language (MSIL) code that implements the types. 
 A set of resources.

What is GC (Garbage Collection) and how it works

One of the good features of the CLR is Garbage Collection, which runs in the background collecting unused object references, freeing us from having to ensure we always destroy them. In reality the time difference between you releasing the object instance and it being garbage collected is likely to be very small, since the GC is always running.
[The process of transitively tracing through all pointers to actively used objects in order to locate all objects that can be referenced, and then arranging to reuse any heap memory that was not found during this trace. The common language runtime garbage collector also compacts the memory that is in use to reduce the working space needed for the heap.]
Heap:
A portion of memory reserved for a program to use for the temporary storage of data structures whose existence or size cannot be determined until the program is running.
Differnce between Managed code and unmanaged code ?
Managed Code:
Code that runs under a “contract of cooperation” with the common language runtime. Managed code must supply the metadata necessary for the runtime to provide services such as memory management, cross-language integration, code access security, and automatic lifetime control of objects. All code based on Microsoft intermediate language (MSIL) executes as managed code.
Un-Managed Code:
Code that is created without regard for the conventions and requirements of the common language runtime. Unmanaged code executes in the common language runtime environment with minimal services (for example, no garbage collection, limited debugging, and so on).
What is MSIL, IL, CTS and, CLR ?
MSIL: (Microsoft intermediate language)
When compiling to managed code, the compiler translates your source code into Microsoft intermediate language (MSIL), which is a CPU-independent set of instructions that can be efficiently converted to native code. MSIL includes instructions for loading, storing, initializing, and calling methods on objects, as well as instructions for arithmetic and logical operations, control flow, direct memory access, exception handling, and other operations. Before code can be executed, MSIL must be converted to CPU-specific code, usually by a just-in-time (JIT) compiler. Because the common language runtime supplies one or more JIT compilers for each computer architecture it supports, the same set of MSIL can be JIT-compiled and executed on any supported architecture.
When a compiler produces MSIL, it also produces metadata. Metadata describes the types in your code, including the definition of each type, the signatures of each type’s members, the members that your code references, and other data that the runtime uses at execution time. The MSIL and metadata are contained in a portable executable (PE) file that is based on and extends the published Microsoft PE and Common Object File Format (COFF) used historically for executable content. This file format, which accommodates
MSIL or native code as well as metadata, enables the operating system to recognize common language runtime images. The presence of metadata in the file along with the MSIL enables your code to describe itself, which means that there is no need for type libraries or Interface Definition Language (IDL). The runtime locates and extracts the metadata from the file as needed during execution.
IL: (Intermediate Language)
A language used as the output of a number of compilers and as the input to a just-in-time (JIT) compiler. The common language
runtime includes a JIT compiler for converting MSIL to native code.
CTS: (Common Type System)
The specification that determines how the common language runtime defines, uses, and manages types
CLR: (Common Language Runtime)
The engine at the core of managed code execution. The runtime supplies managed code with services such as cross-language integration, code access security, object lifetime management, and debugging and profiling support.

What is Reference type and value type ?

Reference Type:
Reference types are allocated on the managed CLR heap, just like object types.
A data type that is stored as a reference to the value’s location. The value of a reference type is the location of the sequence of bits that represent the type’s data. Reference types can be self-describing types, pointer types, or interface types
Value Type:
Value types are allocated on the stack just like primitive types in VBScript, VB6 and C/C++. Value types are not instantiated using new go out of scope when the function they are defined within returns.
Value types in the CLR are defined as types that derive from system.valueType.
A data type that fully describes a value by specifying the sequence of bits that constitutes the value’s representation. Type information for a value type instance is not stored with the instance at run time, but it is available in metadata. Value type instances can be treated as objects using boxing.
What is Boxing and unboxing ?
Boxing:
The conversion of a value type instance to an object, which implies that the instance will carry full type information at run time and will be allocated in the heap. The Microsoft intermediate language (MSIL) instruction set’s box instruction converts a value type to an object by making a copy of the value type and embedding it in a newly allocated object.
Un-Boxing:
The conversion of an object instance to a value type.

What is JIT and how is works ?

An acronym for “just-in-time,” a phrase that describes an action that is taken only when it becomes necessary, such as just-in-time compilation or just-in-time object activation

What is portable executable (PE) ?

The file format used for executable programs and for files to be linked together to form executable programs
What is strong name?
A name that consists of an assembly’s identity—its simple text name, version number, and culture information (if provided)—strengthened by a public key and a digital signature generated over the assembly. Because the assembly manifest contains file hashes for all the files that constitute the assembly implementation, it is sufficient to generate the digital signature over just the one file in the assembly that contains the assembly manifest. Assemblies with the same strong name are expected to be identical
What is global assembly cache?
A machine-wide code cache that stores assemblies specifically installed to be shared by many applications on the computer. Applications deployed in the global assembly cache must have a strong name.

What is difference between constants, readonly and, static ?Constants: The value can’t be changed

Read-only: The value will be initialized only once from the constructor of the class.
Static: Value can be initialized once.
What is difference between shared and public?
An assembly that can be referenced by more than one application. An assembly must be explicitly built to be shared by giving it a cryptographically strong name.

What is namespace used for loading assemblies at run time and name the methods?System.Reflection

What are the types of authentication in .net?
We have three types of  authentication:
  1. Form authentication
  2. Windows authentication
  3. Passport
This has to be declared in web.config file.

What is the difference between a Struct and a Class ?

The struct type is suitable for representing lightweight objects such as Point, Rectangle, and Color. Although it is possible to represent a point as a class, a struct is more efficient in some scenarios. For example, if you declare an array of 1000 Point objects, you will allocate additional memory for referencing each object. In this case, the struct is less expensive. When you create a struct object using the new operator, it gets created and the appropriate constructor is called. Unlike classes, structs can be instantiated without using the new operator. If you do not use new, the fields will remain unassigned and the object cannot be used until all of the fields are initialized. It is an error to declare a default (parameterless) constructor for a struct. A default constructor is always provided to initialize the struct members to their default values.
It is an error to initialize an instance field in a struct. There is no inheritance for structs as there is for classes. A struct cannot inherit from another struct or class, and it cannot be the base of a class. Structs, however, inherit from the base class Object. A struct can implement interfaces, and it does that exactly as classes do. A struct is a value type, while a class is a reference type.

How big is the datatype int in .NET?

32 bits.

How big is the char?

16 bits (Unicode).

How do you initiate a string without escaping each backslash?

Put an @ sign in front of the double-quoted string.

What’s the access level of the visibility type internal?

Current application.

Explain encapsulation ?

The implementation is hidden, the interface is exposed.

What data type should you use if you want an 8-bit value that’s signed?

sbyte.

Speaking of Boolean data types, what’s different between C# and C/C++?

There’s no conversion between 0 and false, as well as any other number and true, like in C/C++.

Where are the value-type variables allocated in the computer RAM?

Stack.

Where do the reference-type variables go in the RAM?

The references go on the stack, while the objects themselves go on the heap.

What is the difference between the value-type variables and reference-type variables in terms of garbage collection?

The value-type variables are not garbage-collected, they just fall off the stack when they fall out of scope, the reference-type objects are picked up by GC when their references go null.

How do you convert a string into an integer in .NET?

Int32.Parse(string)

How do you box a primitive data type variable?

Assign it to the object, pass an object.

Why do you need to box a primitive variable?

To pass it by reference.

What’s the difference between Java and .NET garbage collectors?

Sun left the implementation of a specific garbage collector up to the JRE developer, so their performance varies widely, depending on whose JRE you’re using. Microsoft standardized on their garbage collection.

How do you enforce garbage collection in .NET?

System.GC.Collect();

What’s different about namespace declaration when comparing that to package declaration in Java? No semicolon.

What’s the difference between const and readonly?

You can initialize readonly variables to some runtime values. Let’s say your program uses current date and time as one of the values that won’t change. This way you declare public readonly string DateT = new DateTime().ToString().

What happens when you encounter a continue statement inside the for loop?

The code for the rest of the loop is ignored, the control is transferred back to the beginning of the loop.

What’s the advantage of using System.Text.StringBuilder over System.String?

StringBuilder is more efficient in the cases, where a lot of manipulation is done to the text. Strings are immutable, so each time it’s being operated on, a new instance is created.

Can you store multiple data types in System.Array?

No.

What’s the difference between the System.Array.CopyTo() and System.Array.Clone()?

The first one performs a deep copy of the array, the second one is shallow.

How can you sort the elements of the array in descending order?

By calling Sort() and then Reverse() methods.

What’s the .NET datatype that allows the retrieval of data by a unique key?

HashTable.

What’s class SortedList underneath?

A sorted HashTable.

Will finally block get executed if the exception had not occurred?

Yes.

Can multiple catch blocks be executed?

No, once the proper catch code fires off, the control is transferred to the finally block (if there are any), and then whatever follows the finally block.

Why is it a bad idea to throw your own exceptions?

Well, if at that point you know that an error has occurred, then why not write the proper code to handle that error instead of passing a new Exception object to the catch block? Throwing your own exceptions signifies some design flaws in the project.

What’s a delegate?

A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers.

What’s a multicast delegate?

It’s a delegate that points to and eventually fires off several methods.

How’s the DLL Hell problem solved in .NET?

Assembly versioning allows the application to specify not only the library it needs to run (which was available under Win32),  but also the version of the assembly.

What are the ways to deploy an assembly?

An MSI installer, a CAB archive, and XCOPY command.

What’s a satellite assembly?

When you write a multilingual or multi-cultural application in .NET, and want to distribute the core application separately from the localized modules, the localized assemblies that modify the core application are called satellite assemblies.

What namespaces are necessary to create a localized application?

System.Globalization, System.Resources.
What does assert() do?
In debug compilation, assert takes in a Boolean condition as a parameter, and shows the error dialog if the condition is  false. The program proceeds without any interruption if the condition is true.

What’s the difference between the Debug class and Trace class?

Documentation looks the same. Use Debug class for debug builds, use Trace class for both debug and release builds.

Why are there five tracing levels in System.Diagnostics.TraceSwitcher?

The tracing dumps can be quite verbose and for some applications that are constantly running you run the risk of overloading the machine and the hard drive there. Five levels range from None to Verbose, allowing to fine-tune the tracing activities.

Where is the output of TextWriterTraceListener redirected?

To the Console or a text file depending on the parameter passed to the constructor.

What namespaces are necessary to create a localized application?

System.Globalization, System.Resources.
What are three test cases you should go through in unit testing? 
Positive test cases (correct data, correct output), negative test cases (broken or missing data, proper handling), exception  test cases (exceptions are thrown and caught properly).

Can you change the value of a variable while debugging a C# application?

Yes, if you are debugging via Visual Studio.NET, just go to Immediate window.

What’s the implicit name of the parameter that gets passed into the class’ set method?

Value, and it’s datatype depends on whatever variable we’re changing.

How do you inherit from a class in C#?

Place a colon and then the name of the base class. Notice that it’s double colon in C++.
Does C# support multiple inheritance?
No, use interfaces instead.

When you inherit a protected class-level variable, who is it available to?

Derived Classes.
What’s the top .NET class that everything is derived from?
System.Object.

How’s method overriding different from overloading?

When overriding, you change the method behavior for a derived class. Overloading simply involves having a method with the  same name within the class.
What does the keyword virtual mean in the method definition?
The method can be over-ridden.

Can you declare the override method static while the original method is non-static?

No, you can’t, the signature of the virtual method must remain the same, only the keyword virtual is changed to keyword  override.

Can you override private virtual methods?

No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access.

Can you prevent your class from being inherited and becoming a base class for some other classes?

Yes, that’s what keyword sealed in the class definition is for. The developer trying to derive from your class will get a  message: cannot inherit from Sealed class WhateverBaseClassName. It’s the same concept as final class in Java.
Can you allow class to be inherited, but prevent the method from being over-ridden?
Yes, just leave the class public and make the method sealed.

Why can’t you specify the accessibility modifier for methods inside the interface?

They all must be public. Therefore, to prevent you from getting the false impression that you have any freedom of choice, you are not allowed to specify any accessibility, it’s public by default.
Can you inherit multiple interfaces?
Yes, why not.

And if they have conflicting method names?

It’s up to you to implement the method inside your own class, so implementation is left entirely up to you. This might cause a problem on a higher-level scale if similarly named methods from different interfaces expect different data, but as far as compiler cares you’re okay.

What’s the difference between an interface and abstract class?

In the interface all methods must be abstract, in the abstract class some methods can be concrete. In the interface no accessibility modifiers are allowed, which is ok in abstract classes.

How can you overload a method?

Different parameter data types, different number of parameters, different order of parameters.

If a base class has a bunch of overloaded constructors, and an inherited class has another bunch of overloaded constructors, can you enforce a call from an inherited constructor to an arbitrary base constructor?

Yes, just place a colon, and then keyword base (parameter list to invoke the appropriate constructor) in the overloaded constructor definition inside the inherited class.

What’s the difference between System.String and System.StringBuilder classes?

System.String is immutable, System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed.
Does C# support multiple-inheritance?
No, use interfaces instead.

When you inherit a protected class-level variable, who is it available to?

The derived class.
Are private class-level variables inherited?
Yes, but they are not accessible.  Although they are not visible or accessible via the class interface, they are inherited.

Describe the accessibility modifier “protected internal”.

It is available to derived classes and classes within the same Assembly (and naturally from the base class it’s declared in).
What’s the top .NET class that everything is derived from?
System.Object.

What’s the advantage of using System.Text.StringBuilder over System.String?

StringBuilder is more efficient in cases where there is a large amount of string manipulation.  Strings are immutable, so each time it’s being operated on, a new instance is created.
Can you store multiple data types in System.Array?
No.

What’s the .NET class that allows the retrieval of a data element using a unique key?

HashTable.

Will the finally block get executed if an exception has not occurred?

Yes.

What’s an abstract class?A class that cannot be instantiated.  An abstract class is a class that must be inherited and have the methods overridden. An abstract class is essentially a blueprint for a class without any implementation.

When do you absolutely have to declare a class as abstract?
  1. When at least one of the methods in the class is abstract.
  2. When the class itself is inherited from an abstract class, but not all base abstract methods have been overridden.
What’s an interface?
It’s an abstract class with public abstract methods all of which must be implemented in the inherited classes.

Why can’t you specify the accessibility modifier for methods inside the interface?

They all must be public.  Therefore, to prevent you from getting the false impression that you have any freedom of choice, you are not allowed to specify any accessibility, it’s public by default.

What’s the difference between an interface and abstract class?

In an interface class, all methods must be abstract.  In an abstract class some methods can be concrete.  In an interface class, no accessibility modifiers are allowed, which is ok in an abstract class.

How is method overriding different from method overloading?

When overriding a method, you change the behavior of the method for the derived class. Overloading a method simply involves having another method with the same name within the class.

Can you declare an override method to be static if the original method is non-static?

No. The signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override.

Can you override private virtual methods?

No.  Private methods are not accessible outside the class.
Can you write a class without specifying namespace? Which namespace does it belong to by default? 
Yes, you can, then the class belongs to global namespace which has no name. For commercial products, naturally, you  wouldn’t want global namespace.


What is a formatter?  

A formatter is an object that is responsible for encoding and serializing data into messages on one end, and deserializing  and decoding messages into data on the other end.
 
Different b/w .NET & J2EE ?
Differences between J2EE and the .NET Platform
Vendor Neutrality
The .NET platform is not vendor neutral, it is tied to the Microsoft operating systems. But neither are any of the J2EE implementations Many companies buy into J2EE believing that it will give them vendor neutrality. And, in fact, this is a stated goal of Sun’s vision:
A wide variety of J2EE product configurations and implementations, all of which meet the requirements of this specification, are possible. A portable J2EE application will function correctly when successfully deployed in any of these products. (ref : Java 2 Platform Enterprise Edition Specification, v1.3, page 2-7 available at http://java.sun.com/j2ee/)
Overall Maturity
Given that the .NET platform has a three year lead over J2EE, it should be no surprise to learn that the .NET platform is far more mature than the J2EE platform. Whereas we have high volume highly reliable web sites using .NET technologies (NASDAQ and Dell being among many examples)
Interoperability and Web Services
The .NET platform eCollaboration model is, as I have discussed at length, based on the UDDI and SOAP standards. These standards are widely supported by more than 100 companies. Microsoft, along with IBM and Ariba, are the leaders in this area. Sun is a member of the UDDI consortium and recognizes the importance of the UDDI standards. In a recent press release, Sun’s George Paolini, Vice President for the Java Community Development,  says:
“Sun has always worked to help establish and support open, standards-based technologies that facilitate the growth of network-based applications, and we see UDDI as an important project to establish a registry framework for business-to-business e-commerce
But while Sun publicly says it believes in the UDDI standards, in reality, Sun has done nothing whatsoever to incorporate any of the UDDI standards into J2EE.
Scalability
Typical Comparision w.r.t Systems and their costs
J2EE
Company System Total Sys. Cost
Bull Escala T610 c/s 16,785 $1,980,179
IBM RS/6000 Enterprise Server F80 16,785 $2,026,681
Bull Escala EPC810 c/s 33,375 $3,037,499
IBM RS/6000 Enterprise Server M80 33,375 $3,097,055
Bull Escala EPC2450 110,403 $9,563,263
IBM IBM eServer pSeries 680 Model 7017-S85 110,403 $9,560,594

.NET platform systems

Company System Total Sys. Cost
Dell PowerEdge 4400 16,263 $273,487
Compaq ProLiant ML-570-6/700-3P 20,207 $201,717
Dell PowerEdge 6400 30,231 $334,626
IBM Netfinity 7600 c/s 32,377 $443,463
Compaq ProLiant 8500-X550-64P 161,720 $3,534,272
Compaq ProLiant 8500-X700-64P 179,658 $3,546,582
Compaq ProLiant 8500-X550-96P 229,914 $5,305,571
Compaq ProLiant 8500-X700-96P 262,244 $5,305,571
Compaq ProLiant 8500-700-192P 505,303 $10,003,826

Framework Support

The .NET platform includes such an eCommerce framework called Commerce Server. At this point, there is no equivalent vendor-neutral framework in the J2EE space. With J2EE, you should assume that you will be building your new eCommerce solution from scratch
Moreover, no matter what [J2EE] vendor you choose, if you expect a component framework that will allow you to quickly field complete e-business applications, you are in for a frustrating experience

Language

In the language arena, the choice is about as simple as it gets. J2EE supports Java, and only Java. It will not support any other language in the foreseeable future. The .NET platform supports every language except Java (although it does support a language that is syntactically and functionally equivalent to Java, C#). In fact, given the importance of the .NET platform as a language independent vehicle, it is likely that any language that comes out in the near future will include support for the .NET platform.
Some companies are under the impression that J2EE supports other languages. Although both IBM’s WebSphere and BEA’s WebLogic support other languages, neither does it through their J2EE technology. There are only two official ways in the J2EE platform to access other languages, one through the Java Native Interface and the other through CORBA interoperability. Sun recommends the later approach. As Sun’s Distinguished Scientist and Java Architect Rick Cattell said in a recent interview.

Portability

The reason that operating system portability is a possibility with J2EE is not so much because of any inherent portability of J2EE, as it is that most of the J2EE vendors support multiple operating systems. Therefore as long as one sticks with a given J2EE vendor and a given database vendor, moving from one operating system to another should be possible. This is probably the single most important benefit in favor of J2EE over the .NET platform, which is limited to the Windows operating system. It is worth noting, however, that Microsoft has submitted the specifications for C# and a subset of the .NET Framework (called the common language infrastructure) to ECMA, the group that standardizes JavaScript.
J2EE offers an acceptable solution to ISVs when the product must be marketed to non-Windows customers, particularly when the J2EE platform itself can be bundled with the ISV’s product as an integrated offering.
If the primary customer base for the ISV is Windows customers, then  the .NET platform should be chosen.  It will provide much better performance at a much lower cost.

Client device independence

The major difference being that with Java, it is the presentation tier programmer that determines the ultimate HTML that will be delivered to the client, and with .NET, it is a Visual Studio.NET control.
This Java approach has three problems. First, it requires a lot of code on the presentation tier, since every possible thin client system requires a different code path. Second, it is very difficult to test the code with every possible thin client system. Third, it is very difficult to add new thin clients to an existing application, since to do so involves searching through, and modifying a tremendous amount of presentation tier logic.
The .NET Framework approach is to write device independent code that interacts with visual controls. It is the control, not the programmer, that is responsible for determining what HTML to deliver, based on the capabilities of the client device.. In the .NET Framework model, one can forget that such a thing as HTML even exists!

Conclusion

Sun’s J2EE vision is based on a family of specifications that can be implemented by many vendors. It is open in the sense that any company can license and implement the technology, but closed in the sense that it is controlled by a single vendor, and a self contained architectural island with very limited ability to interact outside of itself. One of J2EE’s major disadvantages is that the choice of the platform dictates the use of a single programming language, and a programming language that is not well suited for most businesses. One of J2EE’s major advantages is that most of the J2EE vendors do offer operating system portability.
Microsoft’s .NET platform vision is a family of products rather than specifications, with specifications used primarily to define points of interoperability. The major disadvantage of this approach is that if is limited to the Windows platform, so applications written for the .NET platform can only be run on .NET platforms. Their are several important advantages to the .NET platform:
* The cost of developing applications is much lower, since standard business languages can be used and device independent presentation tier logic can be written.
* The cost of running applications is much lower, since commodity hardware platforms (at 1/5 the cost of their Unix counterparts) can be used.
* The ability to scale up is much greater, with the proved ability to support at least ten times the number of clients any J2EE platform has shown itself able to support.
* Interoperability is much stronger, with industry standard eCollaboration built into the platform.
 
What are the Main Features of .NET platform?
Features of .NET Platform are :-
Common Language Runtime
Explains the features and benefits of the common language runtime, a run-time environment that manages the execution of code and provides services that simplify the development process.
Assemblies
Defines the concept of assemblies, which are collections of types and resources that form logical units of functionality. Assemblies are the fundamental units of deployment, version control, reuse, activation scoping, and security permissions.
Application Domains
Explains how to use application domains to provide isolation between applications.
Runtime Hosts
Describes the runtime hosts supported by the .NET Framework, including ASP.NET, Internet Explorer, and shell executables.
Common Type System
Identifies the types supported by the common language runtime.
Metadata and Self-Describing Components
Explains how the .NET Framework simplifies component interoperation by allowing compilers to emit additional declarative information, or metadata, into all modules and assemblies.
Cross-Language Interoperability
Explains how managed objects created in different programming languages can interact with one another.
.NET Framework Security
Describes mechanisms for protecting resources and code from unauthorized code and unauthorized users.
.NET Framework Class Library
Introduces the library of types provided by the .NET Framework, which expedites and optimizes the development process and gives you access to system functionality.
 
What is the use of JIT ?
JIT (Just – In – Time) is a compiler which converts MSIL code to Native Code (ie.. CPU-specific code that runs on the same computer architecture).
Because the common language runtime supplies a JIT compiler for each supported CPU architecture, developers can write a set of MSIL that can be JIT-compiled and run on computers with different architectures. However, your managed code will run only on a specific operating system if it calls platform-specific native APIs, or a platform-specific class library.
JIT compilation takes into account the fact that some code might never get called during execution. Rather than using time and memory to convert all the MSIL in a portable executable (PE) file to native code, it converts the MSIL as needed during execution and stores the resulting native code so that it is accessible for subsequent calls. The loader creates and attaches a stub to each of a type’s methods when the type is loaded. On the initial call to the method, the stub passes control to the JIT compiler, which converts the MSIL for that method into native code and modifies the stub to direct execution to the location of the native code. Subsequent calls of the JIT-compiled method proceed directly to the native code that was previously generated, reducing the time it takes to JIT-compile and run the code.
 
What meant of assembly & global assembly cache (gac) & Meta data.
Assembly :– An assembly is the primary building block of a .NET based application. It is a collection of functionality that is built, versioned, and deployed as a single implementation unit (as one or more files). All managed types and resources are marked either as accessible only within their implementation unit, or as accessible by code outside that unit. It overcomes the problem of ‘dll Hell’.The .NET Framework uses assemblies as the fundamental unit for several purposes:
  •  Security
  •  Type Identity
  •  Reference Scope
  • Versioning
  •  Deployment
Global Assembly Cache :– Assemblies can be shared among multiple applications on the machine by registering them in global Assembly cache(GAC). GAC is a machine wide a local cache of assemblies maintained by the .NET Framework. We can register the assembly to global assembly cache by using gacutil command.
We can Navigate to the GAC directory, C:\winnt\Assembly in explore. In the tools menu select the cache properties; in the windows displayed you can set the memory limit in MB used by the GAC
MetaData :–Assemblies have Manifests. This Manifest contains Metadata information of the Module/Assembly as well as it contains detailed Metadata of other assemblies/modules references (exported). It’s the Assembly Manifest which differentiates between an Assembly and a Module.
 
What are the mobile devices supported by .net platform
The Microsoft .NET Compact Framework is designed to run on mobile devices such as mobile phones, Personal Digital Assistants (PDAs), and embedded devices. The easiest way to develop and test a Smart Device Application is to use an emulator.
These devices are divided into two main divisions:
  1. Those that are directly supported by .NET (Pocket PCs, i-Mode phones, and WAP devices)
  2. Those that are not (Palm OS and J2ME-powered devices).
What is GUID , why we use it and where?
GUID :– GUID is Short form of Globally Unique Identifier, a unique 128-bit number that is produced by the Windows OS or by some Windows applications to identify a particular component, application, file, database entry, and/or user. For instance, a Web site may generate a GUID and assign it to a user’s browser to record and track the session. A GUID is also used in a Windows registry to identify COM DLLs. Knowing where to look in the registry and having the correct GUID yields a lot information about a COM object (i.e., information in the type library, its physical location, etc.). Windows also identifies user accounts by a username (computer/domain and username) and assigns it a GUID. Some database administrators even will use GUIDs as primary key values in databases.
GUIDs can be created in a number of ways, but usually they are a combination of a few unique settings based on specific point in time (e.g., an IP address, network MAC address, clock date/time, etc.).


Describe the difference between inline and code behind – which is best in a loosely coupled solution

ASP.NET supports two modes of page development: Page logic code that is written inside runat=”server”> blocks within an .aspx file and dynamically compiled the first time the page is requested on the server. Page logic code that is written within an external class that is compiled prior to deployment on a server and linked “”behind”” the .aspx file at run time.
 
Whats MSIL, and why should my developers need an appreciation of it if at all?
When compiling the source code to managed code, the compiler translates the source into Microsoft intermediate language (MSIL). This is a CPU-independent set of instructions that can efficiently be converted to native code. Microsoft intermediate language (MSIL) is a translation used as the output of a number of compilers. It is the input to a just-in-time (JIT) compiler. The Common Language Runtime includes a JIT compiler for the conversion of MSIL to native code.
Before Microsoft Intermediate Language (MSIL) can be executed it, must be converted by the .NET Framework just-in-time (JIT) compiler to native code. This is CPU-specific code that runs on the same computer architecture as the JIT compiler. Rather than using time and memory to convert all of the MSIL in a portable executable (PE) file to native code. It converts the MSIL as needed whilst executing, then caches the resulting native code so its accessible for any subsequent calls.
 
How many .NET languages can a single .NET DLL contain?
One


What type of code (server or client) is found in a Code-Behind class?

Server
 
Whats an assembly?
Assemblies are the building blocks of .NET Framework applications; they form the fundamental unit of deployment, version control, reuse, activation scoping, and security permissions. An assembly is a collection of types and resources that are built to work together and form a logical unit of functionality. An assembly provides the common language runtime with the information it needs to be aware of type implementations. To the runtime, a type does not exist outside the context of an assembly.
 
How many classes can a single .NET DLL contain?
Unlimited.
 
What is the difference between string and String ?
No difference


What is manifest?

It is the metadata that describes the assemblies.
 
What is metadata?
Metadata is machine-readable information about a resource, or “”data about data.”” Such information might include details on content, format, size, or other characteristics of a data source. In .NET, metadata includes type definitions, version information, external assembly references, and other standardized information.


What are the types of assemblies?

There are four types of assemblies in .NET:
Static assemblies These are the .NET PE files that you create at compile time.
Dynamic assemblies
These are PE-formatted, in-memory assemblies that you dynamically create at runtime using the classes in the System.Reflection.Emit namespace.
Private assemblies
These are static assemblies used by a specific application.
Public or shared assemblies
These are static assemblies that must have a unique shared name and can be used by any application.
An application uses a private assembly by referring to the assembly using a static path or through an XML-based application configuration file. While the CLR doesn’t enforce versioning policies-checking whether the correct version is used-for private assemblies, it ensures that an
application uses the correct shared assemblies with which the application was built. Thus, an application uses a specific shared assembly by referring to the specific shared assembly, and the CLR ensures that the correct version is loaded at runtime.
In .NET, an assembly is the smallest unit to which you can associate a version number;
 
What are delegates?where are they used ?
A delegate defines a reference type that can be used to encapsulate a method with a specific signature. A delegate instance encapsulates a static or an instance method. Delegates are roughly similar to function pointers in C++; however, delegates are type-safe and secure.
 
When do you use virutal keyword?.
When we need to override a method of the base class in the sub class, then we give the virtual keyword in the base class method. This makes the method in the base class to be overridable. Methods, properties, and indexers can be virtual, which means that their implementation can be overridden in derived classes.
 
What are class access modifiers ?
Access modifiers are keywords used to specify the declared accessibility of a member or a type. This section introduces the four access modifiers:
  • Public  – Access is not restricted.
  • Protected  – Access is limited to the containing class or types derived fro