Design Patterns – Code Teddy

Singleton Design Pattern In C# – Part Three (Static vs Singleton)

Introduction

In this series on learning singleton pattern, we learned lazy initialization and eager initialization with practical examples. We also learned why it is necessary to make the singleton class sealed with the sealed keyword. In this article, I’ll try to explain the differences between static and singleton class. We will also see where to use static class and where to use singleton classes.

Continue reading “Singleton Design Pattern In C# – Part Three (Static vs Singleton)”

Singleton Design Pattern In C# – Part 2 (Eager and Lazy Initialization in Singleton)

Introduction

In the previous article on learning singleton pattern, we discussed what is singleton design pattern, when is it needed and what problems it solves. We also discussed how to create a basic singleton class step by step and how to enhance that class to be thread-safe with the help of locking and performance effective with the help of double check locking. In this article, we’ll discuss Lazy initialization, the lazy keyword, why to make singleton class a sealed class, and what are the differences between singleton and static class. Before we start, I strongly recommend you go through my last article.

Continue reading “Singleton Design Pattern In C# – Part 2 (Eager and Lazy Initialization in Singleton)”

Singleton Design Pattern in C# – Part 1

Introduction

I always wanted to write on Singleton design pattern in C#. Though there already are many posts available on Singleton design pattern, I’ll try to cover this topic in the most simplistic and easy to understand way.

Continue reading “Singleton Design Pattern in C# – Part 1”

RESTful Day #6: Request logging and Exception handling/logging in Web APIs using Action Filters, Exception Filters and NLog

Download Source Code from GitHub

Introduction

We have been learning a lot about WebAPI, its uses, implementations, and security aspects since last five articles of the series. This article of the series will explain how we can handle requests and log them for tracking and for the sake of debugging, how we can handle exceptions and log them. We’ll follow a centralized way of handling exceptions in WebAPI and write our custom classes to be mapped to the type of exception that we encounter and log the accordingly. I’ll use NLog to log requests and exceptions as well. We’ll leverage the capabilities of Exception Filters and Action Filters to centralize request logging and exception handling in WebAPI.

Roadmap

The following is the roadmap I have setup to learn WebAPI step by step,

I’ll purposely use Visual Studio 2010 and .NET Framework 4.0 because there are few implementations that are very hard to find in .NET Framework 4.0, but I’ll make it easy by showing how we can do it.

Request Logging

Since we are writing web services, we are exposing our end points. We must know where the requests are coming from and what requests are coming to our server. Logging could be very beneficial and helps us in a lot of ways like, debugging, tracing, monitoring and analytics.

We already have an existing design. If you open the solution, you’ll get to see the structure as mentioned below or one can also implement this approach in their existing solution as well.

Setup NLog in WebAPI

NLog serves various purposes but primarily logging. We’ll use NLog for logging into files and windows event as well. You can read more about NLog at http://NLog-project.org/

One can use the sample application that we used in Day#5 or can have any other application as well. I am using the existing sample application that we were following throughout all the parts of this series. Our application structure looks something like:

Step 1: Download NLog Package

Right click WebAPI project and select manage Nuget Packages from the list. When the Nuget Package Manager appears, search for NLog. You’ll get Nlog like shown in image below, just install it to our project.

After adding this you will find following NLog dll referenced in your application.

Step 2: Configuring NLog

To configure NLog with application add following settings in our existing WebAPI web.config file,

ConfigSection –

Configuration Section – I have added the section to configuration and defined the path and format dynamic target log file name, also added the eventlog source to Api Services.

As mentioned in above target path, I have also created to “APILog” folder in the base directory of application.

Now we have configured the NLog in our application, and it is ready to start work for request logging. Note that in the rules section we have defined rules for logging in files as well as in windows events log as well, you can choose both of them or can opt for one too. Let’s start with logging request in application, with action filters –

NLogger Class

Add a folder “Helpers” in the API, which will segregate the application code for readability, better understanding and maintainability.

To start add our main class “NLogger“, which will responsible for all types of errors and info logging, to same Helper folder. Here NLogger class implements ITraceWriter interface, which provides “Trace” method for the service request.

#region Using namespaces.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Http.Tracing;
using NLog;
using System.Net.Http;
using System.Text;
using WebApi.ErrorHelper;
#endregion

namespace WebApi.Helpers
{
    /// <summary>
    /// Public class to log Error/info messages to the access log file
    /// </summary>
    public sealed class NLogger : ITraceWriter
    {
        #region Private member variables.
        private static readonly Logger ClassLogger = LogManager.GetCurrentClassLogger();

        private static readonly Lazy<Dictionary<TraceLevel, Action<string>>> LoggingMap = new Lazy<Dictionary<TraceLevel, Action<string>>>(() => new Dictionary<TraceLevel, Action<string>> { { TraceLevel.Info, ClassLogger.Info }, { TraceLevel.Debug, ClassLogger.Debug }, { TraceLevel.Error, ClassLogger.Error }, { TraceLevel.Fatal, ClassLogger.Fatal }, { TraceLevel.Warn, ClassLogger.Warn } });
        #endregion

        #region Private properties.
        /// <summary>
        /// Get property for Logger
        /// </summary>
        private Dictionary<TraceLevel, Action<string>> Logger
        {
            get { return LoggingMap.Value; }
        }
        #endregion

        #region Public member methods.
        /// <summary>
        /// Implementation of TraceWriter to trace the logs.
        /// </summary>
        /// <param name="request"></param>
        /// <param name="category"></param>
        /// <param name="level"></param>
        /// <param name="traceAction"></param>
        public void Trace(HttpRequestMessage request, string category, TraceLevel level, Action traceAction)
        {
            if (level != TraceLevel.Off)
            {
                if (traceAction != null && traceAction.Target != null)
                {
                    category = category + Environment.NewLine + "Action Parameters : " + traceAction.Target.ToJSON();
                }
                var record = new TraceRecord(request, category, level);
                if (traceAction != null) traceAction(record);
                Log(record);
            }
        }
        #endregion

        #region Private member methods.
        /// <summary>
        /// Logs info/Error to Log file
        /// </summary>
        /// <param name="record"></param>
        private void Log(TraceRecord record)
        {
            var message = new StringBuilder();

            if (!string.IsNullOrWhiteSpace(record.Message))
                message.Append("").Append(record.Message + Environment.NewLine);

            if (record.Request != null)
            {
                if (record.Request.Method != null)
                    message.Append("Method: " + record.Request.Method + Environment.NewLine);

                if (record.Request.RequestUri != null)
                    message.Append("").Append("URL: " + record.Request.RequestUri + Environment.NewLine);

                if (record.Request.Headers != null && record.Request.Headers.Contains("Token") && record.Request.Headers.GetValues("Token") != null && record.Request.Headers.GetValues("Token").FirstOrDefault() != null)
                    message.Append("").Append("Token: " + record.Request.Headers.GetValues("Token").FirstOrDefault() + Environment.NewLine);
            }

            if (!string.IsNullOrWhiteSpace(record.Category))
                message.Append("").Append(record.Category);

            if (!string.IsNullOrWhiteSpace(record.Operator))
                message.Append(" ").Append(record.Operator).Append(" ").Append(record.Operation);

            
            Logger[record.Level](Convert.ToString(message) + Environment.NewLine);
        }
        #endregion
    }
}

Adding Action Filter

Action filter will be responsible for handling all the incoming requests to our APIs and logging them using NLogger class. We have “OnActionExecuting” method that is implicitly called if we mark our controllers or global application to use that particular filter. So each time any action of any controller will be hit, our “OnActionExecuting” method will execute to log the request.

Step 1: Adding LoggingFilterAttribute class

Create a class LoggingFilterAttribute to “ActionFilters” folder and add following code.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Http.Filters;
using System.Web.Http.Controllers;
using System.Web.Http.Tracing;
using System.Web.Http;
using WebApi.Helpers;


namespace WebApi.ActionFilters
{
    public class LoggingFilterAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(HttpActionContext filterContext)
        {
            GlobalConfiguration.Configuration.Services.Replace(typeof(ITraceWriter), new NLogger());
            var trace = GlobalConfiguration.Configuration.Services.GetTraceWriter();
            trace.Info(filterContext.Request, "Controller : " + filterContext.ControllerContext.ControllerDescriptor.ControllerType.FullName + Environment.NewLine + "Action : " + filterContext.ActionDescriptor.ActionName, "JSON", filterContext.ActionArguments);
        }
    }
}

The LoggingFilterAttribute class derived from ActionFilterAttribute, which is underSystem.Web.Http.Filters and overriding the OnActionExecuting method.

Here I have replaced the default “ITraceWriter” service with our NLogger class instance in the controller’s service container. Now GetTraceWriter() method will return our instance (instance NLogger class) and Info() will call trace() method of our NLogger class.

Note that the code below.

GlobalConfiguration.Configuration.Services.Replace(typeof(ITraceWriter), new NLogger());

is used to resolve dependency between ITaceWriter and NLogger class. Thereafter we use a variable namedtrace to get the instance and trace.Info() is used to log the request and whatever text we want to add along with that request.

Step 2: Registering Action Filter (LoggingFilterAttribute)

In order to register the created action filter to application’s filters, just add a new instance of your action filter toconfig.Filters in WebApiConfig class.

using System.Web.Http;
using WebApi.ActionFilters;

namespace WebApi.App_Start
{
    public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            config.Filters.Add(new LoggingFilterAttribute());
        }
    }
}

Now this action filter is applicable to all the controllers and actions in our project. You may not believe but request logging is done. It’s time to run the application and validate our homework.

Image credit: https://pixabay.com/en/social-media-network-media-54536/

Running the application

Let’s run the application and try to make a call, using token based authorization, we have already covered authorization in day#5. You first need to authenticate your request using login service and then that service will return a token for making calls to other services. Use that token to make calls to other services. For more details you can read day 5 of this series.

Just run the application, we get

We already have our test client added, but for new readers, just go to Manage Nuget Packages, by right clicking WebAPI project and typing WebAPITestClient in searchbox in online packages

You’ll get “A simple Test Client for ASP.NET Web API”, just add it. You’ll get a help controller in Areas-> HelpPage like shown below:

I have already provided the database scripts and data in my previous article, you can use the same.

Append “/help” in the application url, and you’ll get the test client,

GET:

POST:

PUT:

DELETE:

You can test each service by clicking on it. Once you click on the service link, you’ll be redirected to test the service page of that particular service. On that page there is a button Test API in the right bottom corner, just press that button to test your service:

Service for Get All products:

In the below case, I have already generated the token and now I am using it to make call to fetch all the products from the products table in the database.

Here I have called allproducts API, Add the value for parameter Id and “Token” header with its current value and click to get the result:

Now let’s see what happens to our APILog folder in application. Here you find the API log has been created, with the same name we have configured in NLog configuration in web.config file. The log file contains all the supplied details like Timestamp, Method type, URL , Header information (Token), Controller name, action and action parameters. You can also add more details to this log which you deem important for your application.

Logging Done!

Exception Logging

Our logging setup is completed, now we’ll focus on centralizing exception logging as well, so that none of the exception escapes without logging itself. Logging exception is of very high importance, it keeps track of all the exceptions. No matter business or application or system exceptions, all of them have to be logged.

Implementing Exception logging

Step 1: Exception Filter Attribute

Now we will add an action filter in our application for logging the exceptions. For this create a class,GlobalExceptionAttribute to “ActionFilter” folder and add the code below, the class is derived fromExceptionFilterAttribute, which is under System.Web.Http.Filters.

I override the OnException() method and replace the default “ITraceWriter” service with our NLogger class instance in the controller’s service container, same as we have done in Action logging in above section. Now theGetTraceWriter() method will return our instance (instance NLogger class) and Info() will call trace()method of NLogger class.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Http.Filters;
using System.Web.Http;
using System.Web.Http.Tracing;
using WebApi.Helpers;
using System.ComponentModel.DataAnnotations;
using System.Net.Http;
using System.Net;

namespace WebApi.ActionFilters
{
    /// <summary>
    /// Action filter to handle for Global application errors.
    /// </summary>
    public class GlobalExceptionAttribute : ExceptionFilterAttribute
    {
        public override void OnException(HttpActionExecutedContext context)
        {
            GlobalConfiguration.Configuration.Services.Replace(typeof(ITraceWriter), new NLogger());
            var trace = GlobalConfiguration.Configuration.Services.GetTraceWriter();
            trace.Error(context.Request, "Controller : " + context.ActionContext.ControllerContext.ControllerDescriptor.ControllerType.FullName + Environment.NewLine + "Action : " + context.ActionContext.ActionDescriptor.ActionName, context.Exception);

            var exceptionType = context.Exception.GetType();

            if (exceptionType == typeof(ValidationException))
            {
                var resp = new HttpResponseMessage(HttpStatusCode.BadRequest) { Content = new StringContent(context.Exception.Message), ReasonPhrase = "ValidationException", };
                throw new HttpResponseException(resp);

            }
            else if (exceptionType == typeof(UnauthorizedAccessException))
            {
                throw new HttpResponseException(context.Request.CreateResponse(HttpStatusCode.Unauthorized));
            }
            else
            {
                throw new HttpResponseException(context.Request.CreateResponse(HttpStatusCode.InternalServerError));
            }
        }
    }
}

Step 2: Modify NLogger Class

Our NLogger class is capable to log all info and events, I have done some changes in private method Log() to handle the exceptions

#region Private member methods.
/// <summary>
/// Logs info/Error to Log file
/// </summary>
/// <param name="record"></param>
private void Log(TraceRecord record)
{
var message = new StringBuilder();

if (!string.IsNullOrWhiteSpace(record.Message))
                message.Append("").Append(record.Message + Environment.NewLine);

      if (record.Request != null)
{
       if (record.Request.Method != null)
            message.Append("Method: " + record.Request.Method + Environment.NewLine);

                if (record.Request.RequestUri != null)
                    message.Append("").Append("URL: " + record.Request.RequestUri + Environment.NewLine);

                if (record.Request.Headers != null && record.Request.Headers.Contains("Token") && record.Request.Headers.GetValues("Token") != null && record.Request.Headers.GetValues("Token").FirstOrDefault() != null)
                    message.Append("").Append("Token: " + record.Request.Headers.GetValues("Token").FirstOrDefault() + Environment.NewLine);
            }

            if (!string.IsNullOrWhiteSpace(record.Category))
                message.Append("").Append(record.Category);

            if (!string.IsNullOrWhiteSpace(record.Operator))
                message.Append(" ").Append(record.Operator).Append(" ").Append(record.Operation);

            if (record.Exception != null && !string.IsNullOrWhiteSpace(record.Exception.GetBaseException().Message))
            {
                var exceptionType = record.Exception.GetType();
                message.Append(Environment.NewLine);
                message.Append("").Append("Error: " + record.Exception.GetBaseException().Message + Environment.NewLine);
            }

            Logger[record.Level](Convert.ToString(message) + Environment.NewLine);
        }

Step 3: Modify Controller for Exception

Our application is now ready to run, but there is no exception in our code, so I added a throw exception code inProductController, just the Get(int id) method so that it can throw exception for testing our exception logging mechanism. It will throw an exception if the product is not there in database with the provided id.

  // GET api/product/5
 [GET("productid/{id?}")]
 [GET("particularproduct/{id?}")]
 [GET("myproduct/{id:range(1, 3)}")]
 public HttpResponseMessage Get(int id)
 {
var product = _productServices.GetProductById(id);
      if (product != null)
       return Request.CreateResponse(HttpStatusCode.OK, product);

 throw new Exception("No product found for this id");
      //return Request.CreateErrorResponse(HttpStatusCode.NotFound,   "No product found for this id");
 }

Step 4: Run the application

Run the application and click on Product/all API

Add the parameter id value to 1 and header Token with it’s current value, click on send button to get the result:

Now we can see that the Status is 200/OK, and we also get a product with the provided id in the response body. Let’s see the API log now:

The log has captured the call of Product API, now provide a new product id as parameter, which is not there in database, I am using 12345 as product id and result is:

We can see there is an 500/Internal Server Error now in response status, let’s check the API Log:

Well, now the log has captured both the event and error of same call on the server, you can see call log details and the error with provided error message in the log.

Custom Exception logging

In the above section we have implemented exception logging, but there is default system response and status (i.e. 500/Internal Server Error). It will be always good to have your own custom response and exceptions for your API. That will be easier for client to consume and understand the API responses.

Step 1: Add Custom Exception Classes

Add “Error Helper” folder to application to maintain our custom exception classes separately and add “IApiExceptions” interface to newly created “ErrorHelper” folder –

Add following code the IApiExceptions interface, this will serve as a template for all exception classes, I have added four common properties for our custom classes to maintain Error Code, ErrorDescription, HttpStatus (Contains the values of status codes defined for HTTP) and ReasonPhrase.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;

namespace WebApi.ErrorHelper
{
    /// <summary>
    /// IApiExceptions Interface
    /// </summary>
    public interface IApiExceptions
    {
        /// <summary>
        /// ErrorCode
        /// </summary>
        int ErrorCode { get; set; }
        /// <summary>
        /// ErrorDescription
        /// </summary>
        string ErrorDescription { get; set; }
        /// <summary>
        /// HttpStatus
        /// </summary>
        HttpStatusCode HttpStatus { get; set; }
        /// <summary>
        /// ReasonPhrase
        /// </summary>
        string ReasonPhrase { get; set; }
    }
}

Here, I divided our exceptions in three categories:

API Exceptions – for API level exceptions.
Business Exceptions – for exceptions at business logic level.
Data Exceptions – Data related exceptions.

To implement this create a three new classes ApiException.cs, ApiDataException.cs and ApiBusinessExceptionclasses to same folder which implements IApiExceptions interface with following code to the classes.

#region Using namespaces.
using System;
using System.Net;
using System.Runtime.Serialization;
#endregion


namespace WebApi.ErrorHelper
{
    /// <summary>
    /// Api Exception
    /// </summary>
    [Serializable]
    [DataContract]
    public class ApiException : Exception, IApiExceptions
    {
        #region Public Serializable properties.
        [DataMember]
        public int ErrorCode { get; set; }
        [DataMember]
        public string ErrorDescription { get; set; }
        [DataMember]
        public HttpStatusCode HttpStatus { get; set; }
        
        string reasonPhrase = "ApiException";

        [DataMember]
        public string ReasonPhrase
        {
            get { return this.reasonPhrase; }

            set { this.reasonPhrase = value; }
        }
        #endregion
    }
}

I have initialized ReasonPhrase property with different default values in these classes to differentiate the implementation, you can use implement your custom classes as per your application needs.

The directives applied on class as Serializable and DataContract to make sure that the class defines or implements a data contract is serializable and can be serialize by a serializer.

Note: Add reference of “System.Runtime.Serialization.dll” DLL if you facing any assembly issue.

In the same way add “ApiBusinessException” and “ApiDataException” classes into the same folder, with the following code –

#region Using namespaces.
using System;
using System.Net;
using System.Runtime.Serialization; 
#endregion

namespace WebApi.ErrorHelper
{
    /// <summary>
    /// Api Business Exception
    /// </summary>
    [Serializable]
    [DataContract]
    public class ApiBusinessException : Exception, IApiExceptions
    {
        #region Public Serializable properties.
        [DataMember]
        public int ErrorCode { get; set; }
        [DataMember]
        public string ErrorDescription { get; set; }
        [DataMember]
        public HttpStatusCode HttpStatus { get; set; }

        string reasonPhrase = "ApiBusinessException";

        [DataMember]
        public string ReasonPhrase
        {
            get { return this.reasonPhrase; }

            set { this.reasonPhrase = value; }
        }
        #endregion

        #region Public Constructor.
        /// <summary>
        /// Public constructor for Api Business Exception
        /// </summary>
        /// <param name="errorCode"></param>
        /// <param name="errorDescription"></param>
        /// <param name="httpStatus"></param>
        public ApiBusinessException(int errorCode, string errorDescription, HttpStatusCode httpStatus)
        {
            ErrorCode = errorCode;
            ErrorDescription = errorDescription;
            HttpStatus = httpStatus;
        } 
        #endregion

    }
}

#region Using namespaces.
using System;
using System.Net;
using System.Runtime.Serialization;
#endregion

namespace WebApi.ErrorHelper
{
    /// <summary>
    /// Api Data Exception
    /// </summary>
    [Serializable]
    [DataContract]
    public class ApiDataException : Exception, IApiExceptions
    {
        #region Public Serializable properties.
        [DataMember]
        public int ErrorCode { get; set; }
        [DataMember]
        public string ErrorDescription { get; set; }
        [DataMember]
        public HttpStatusCode HttpStatus { get; set; }

        string reasonPhrase = "ApiDataException";

        [DataMember]
        public string ReasonPhrase
        {
            get { return this.reasonPhrase; }

            set { this.reasonPhrase = value; }
        }

        #endregion

        #region Public Constructor.
        /// <summary>
        /// Public constructor for Api Data Exception
        /// </summary>
        /// <param name="errorCode"></param>
        /// <param name="errorDescription"></param>
        /// <param name="httpStatus"></param>
        public ApiDataException(int errorCode, string errorDescription, HttpStatusCode httpStatus)
        {
            ErrorCode = errorCode;
            ErrorDescription = errorDescription;
            HttpStatus = httpStatus;
        }
        #endregion
    }
}

JSon Serializers

There are some objects need to be serialized in JSON, to log and to transfer through the modules, for this I have add some extension methods to Object class.

For that add “System.Web.Extensions.dll” reference to project and add “JSONHelper” class to Helpers folder, with following code:

#region Using namespaces.
using System.Web.Script.Serialization;
using System.Data;
using System.Collections.Generic;
using System;

#endregion

namespace WebApi.Helpers
{
    public static class JSONHelper
    {
         #region Public extension methods.
        /// <summary>
        /// Extened method of object class, Converts an object to a json string.
        /// </summary>
        /// <param name="obj"></param>
        /// <returns></returns>
        public static string ToJSON(this object obj)
        {
            var serializer = new JavaScriptSerializer();
            try
            {
                return serializer.Serialize(obj);
            }
            catch(Exception ex)
            {
                return "";
            }
        }
         #endregion
    }
}

In the above code “ToJSON()” method is an extension of base Object class, which serializes supplied the object to a JSON string. The method using “JavaScriptSerializer” class which exists in “System.Web.Script.Serialization“.

Modify NLogger Class

For exception handling I have modified the Log() method of NLogger, which will now handle the different API exceptions.

/// <summary>
/// Logs info/Error to Log file
/// </summary>
/// <param name="record"></param>
private void Log(TraceRecord record)
{
var message = new StringBuilder();

      if (!string.IsNullOrWhiteSpace(record.Message))
                message.Append("").Append(record.Message + Environment.NewLine);

            if (record.Request != null)
            {
                if (record.Request.Method != null)
                    message.Append("Method: " + record.Request.Method + Environment.NewLine);

                if (record.Request.RequestUri != null)
                    message.Append("").Append("URL: " + record.Request.RequestUri + Environment.NewLine);

                if (record.Request.Headers != null && record.Request.Headers.Contains("Token") && record.Request.Headers.GetValues("Token") != null && record.Request.Headers.GetValues("Token").FirstOrDefault() != null)
                    message.Append("").Append("Token: " + record.Request.Headers.GetValues("Token").FirstOrDefault() + Environment.NewLine);
            }

            if (!string.IsNullOrWhiteSpace(record.Category))
                message.Append("").Append(record.Category);

            if (!string.IsNullOrWhiteSpace(record.Operator))
                message.Append(" ").Append(record.Operator).Append(" ").Append(record.Operation);

            if (record.Exception != null && !string.IsNullOrWhiteSpace(record.Exception.GetBaseException().Message))
            {
                var exceptionType = record.Exception.GetType();
                message.Append(Environment.NewLine);
                if (exceptionType == typeof(ApiException))
                {
                    var exception = record.Exception as ApiException;
                    if (exception != null)
                    {
                        message.Append("").Append("Error: " + exception.ErrorDescription + Environment.NewLine);
                        message.Append("").Append("Error Code: " + exception.ErrorCode + Environment.NewLine);
                    }
                }
                else if (exceptionType == typeof(ApiBusinessException))
                {
                    var exception = record.Exception as ApiBusinessException;
                    if (exception != null)
                    {
                        message.Append("").Append("Error: " + exception.ErrorDescription + Environment.NewLine);
                        message.Append("").Append("Error Code: " + exception.ErrorCode + Environment.NewLine);
                    }
                }
                else if (exceptionType == typeof(ApiDataException))
                {
                    var exception = record.Exception as ApiDataException;
                    if (exception != null)
                    {
                        message.Append("").Append("Error: " + exception.ErrorDescription + Environment.NewLine);
                        message.Append("").Append("Error Code: " + exception.ErrorCode + Environment.NewLine);
                    }
                }
                else
                    message.Append("").Append("Error: " + record.Exception.GetBaseException().Message + Environment.NewLine);
            }

            Logger[record.Level](Convert.ToString(message) + Environment.NewLine);
        }

The code above checks the exception object of TraceRecord and updates the logger as per the exception type.

Modify GlobalExceptionAttribute

As we have created GlobalExceptionAttribute to handle all exceptions and create response in case of any exception. Now I have added some new code to this in order to enable the GlobalExceptionAttribute class to handle custom exceptions. I am adding only modified method here for your reference .

public override void OnException(HttpActionExecutedContext context)
{
         GlobalConfiguration.Configuration.Services.Replace(typeof(ITraceWriter), new NLogger());
            var trace = GlobalConfiguration.Configuration.Services.GetTraceWriter();
            trace.Error(context.Request, "Controller : " + context.ActionContext.ControllerContext.ControllerDescriptor.ControllerType.FullName + Environment.NewLine + "Action : " + context.ActionContext.ActionDescriptor.ActionName, context.Exception);

            var exceptionType = context.Exception.GetType();

            if (exceptionType == typeof(ValidationException))
            {
                var resp = new HttpResponseMessage(HttpStatusCode.BadRequest) { Content = new StringContent(context.Exception.Message), ReasonPhrase = "ValidationException", };
                throw new HttpResponseException(resp);

            }
            else if (exceptionType == typeof(UnauthorizedAccessException))
            {
                throw new HttpResponseException(context.Request.CreateResponse(HttpStatusCode.Unauthorized, new ServiceStatus() { StatusCode = (int)HttpStatusCode.Unauthorized, StatusMessage = "UnAuthorized", ReasonPhrase = "UnAuthorized Access" }));
            }
            else if (exceptionType == typeof(ApiException))
            {
                var webapiException = context.Exception as ApiException;
                if (webapiException != null)
                    throw new HttpResponseException(context.Request.CreateResponse(webapiException.HttpStatus, new ServiceStatus() { StatusCode = webapiException.ErrorCode, StatusMessage = webapiException.ErrorDescription, ReasonPhrase = webapiException.ReasonPhrase }));
            }
            else if (exceptionType == typeof(ApiBusinessException))
            {
                var businessException = context.Exception as ApiBusinessException;
                if (businessException != null)
                    throw new HttpResponseException(context.Request.CreateResponse(businessException.HttpStatus, new ServiceStatus() { StatusCode = businessException.ErrorCode, StatusMessage = businessException.ErrorDescription, ReasonPhrase = businessException.ReasonPhrase }));
            }
            else if (exceptionType == typeof(ApiDataException))
            {
                var dataException = context.Exception as ApiDataException;
                if (dataException != null)
                    throw new HttpResponseException(context.Request.CreateResponse(dataException.HttpStatus, new ServiceStatus() { StatusCode = dataException.ErrorCode, StatusMessage = dataException.ErrorDescription, ReasonPhrase = dataException.ReasonPhrase }));
            }
            else
            {
                throw new HttpResponseException(context.Request.CreateResponse(HttpStatusCode.InternalServerError));
            }
        }

In the above code I have modified the overrided method OnExeption() and created new Http response exception based on the different exception types.

Modify Product Controller

Now modify the Product controller to throw our custom exception form, please look into the Get method I have modified to throw the APIDataException in case if data is not found and APIException in any other kind of error.

// GET api/product/5
[GET("productid/{id?}")]
[GET("particularproduct/{id?}")]
[GET("myproduct/{id:range(1, 3)}")]
public HttpResponseMessage Get(int id)
{
if (id != null)
      {
       var product = _productServices.GetProductById(id);
            if (product != null)
             return Request.CreateResponse(HttpStatusCode.OK, product);

throw new ApiDataException(1001, "No product found for this id.", HttpStatusCode.NotFound);
      }
      throw new ApiException() { ErrorCode = (int)HttpStatusCode.BadRequest, ErrorDescription = "Bad Request..." };
}

Run the application

Run the application and click on Product/all API:

Add the parameter id value to 1 and header Token with its current value, click on send button to get the result:

Now we can see that the Status is 200/OK, and we also get a product with the provided id in the response body. Lets see the API log now –

The log has captured the call of Product API, now provide a new product id as parameter, which is not there in database, I am using 12345 as product id and result is:

We can see, now there is a custom error status code “1001” and messages “No product found for this id.” And the generic status code “500/Internal Server Error” is now replaced with our supplied code “404/ Not Found”, which is more meaningful for the client or consumer.

Lets see the APILog now:

Well, now the log has captured both the event and error of same call on the server, you can see call log details and the error with provided error message in the log with our custom error code, I have only captured error description and error code, but you can add more details in the log as per your application needs.

Update the controller for new Exception Handling

Following is the code for controllers with implementation of custom exception handling and logging:

Product Controller

using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using AttributeRouting;
using AttributeRouting.Web.Http;
using BusinessEntities;
using BusinessServices;
using WebApi.ActionFilters;
using WebApi.Filters;
using System;
using WebApi.ErrorHelper;

namespace WebApi.Controllers
{
    [AuthorizationRequired]
    [RoutePrefix("v1/Products/Product")]
    public class ProductController : ApiController
    {
        #region Private variable.

        private readonly IProductServices _productServices;

        #endregion

        #region Public Constructor

        /// <summary>
        /// Public constructor to initialize product service instance
        /// </summary>
        public ProductController(IProductServices productServices)
        {
            _productServices = productServices;
        }

        #endregion

        // GET api/product
        [GET("allproducts")]
        [GET("all")]
        public HttpResponseMessage Get()
        {
            var products = _productServices.GetAllProducts();
            var productEntities = products as List ?? products.ToList();
            if (productEntities.Any())
                return Request.CreateResponse(HttpStatusCode.OK, productEntities);
            throw new ApiDataException(1000, "Products not found", HttpStatusCode.NotFound);
        }

        // GET api/product/5
        [GET("productid/{id?}")]
        [GET("particularproduct/{id?}")]
        [GET("myproduct/{id:range(1, 3)}")]
        public HttpResponseMessage Get(int id)
        {
            if (id != null)
            {
                var product = _productServices.GetProductById(id);
                if (product != null)
                    return Request.CreateResponse(HttpStatusCode.OK, product);

                throw new ApiDataException(1001, "No product found for this id.", HttpStatusCode.NotFound);
            }
            throw new ApiException() { ErrorCode = (int)HttpStatusCode.BadRequest, ErrorDescription = "Bad Request..." };
        }

        // POST api/product
        [POST("Create")]
        [POST("Register")]
        public int Post([FromBody] ProductEntity productEntity)
        {
            return _productServices.CreateProduct(productEntity);
        }

        // PUT api/product/5
        [PUT("Update/productid/{id}")]
        [PUT("Modify/productid/{id}")]
        public bool Put(int id, [FromBody] ProductEntity productEntity)
        {
            if (id > 0)
            {
                return _productServices.UpdateProduct(id, productEntity);
            }
            return false;
        }

        // DELETE api/product/5
        [DELETE("remove/productid/{id}")]
        [DELETE("clear/productid/{id}")]
        [PUT("delete/productid/{id}")]
        public bool Delete(int id)
        {
            if (id != null && id > 0)
            {
                var isSuccess = _productServices.DeleteProduct(id);
                if (isSuccess)
                {
                    return isSuccess;
                }
                throw new ApiDataException(1002, "Product is already deleted or not exist in system.", HttpStatusCode.NoContent );
            }
            throw new ApiException() {ErrorCode = (int) HttpStatusCode.BadRequest, ErrorDescription = "Bad Request..."};
        }
    }
}

Now you can see, our application is so rich and scalable that none of the exception or transaction can escapelogging.Once setup is inplaced, now you don’t have to worry about writing code each time for logging or requests and exceptions, but you can relax and focus on business logic only.

Image credit: https://pixabay.com/en/kermit-frog-meadow-daisy-concerns-383370/

Conclusion

In this article we learnt about how to perform request logging and exception logging in WebPI. There could be numerous ways in which you can perform these operations but I tried to present this in as simple way as possible. My approach was to take our enterprise level to next level of development, where developers should not always be worried about exception handling and logging. Our solution provides a generic approach of centralizing the operations in one place; all the requests and exceptions are automatically taken care of. In my new articles, I’ll try to enhance the application by explaining unit testing in WebAPI and OData in WebAPI. You can download the complete source code of this article with packages from GitHub. Happy coding

Other Series

My other series of articles:

For more technical articles you can reach out to CodeTeddy.

RESTful Day #3: Resolve dependency of dependencies using Inversion of Control and dependency injection in ASP.NET Web APIs with Unity Container and Managed Extensibility Framework (MEF)

Download Source Code

Introduction

In my last two articles, I explained how to create a RESTful service using ASP.NET Web API working with Entity Framework and resolving dependencies using Unity Container. In this article, I’ll explain how to create a loosely coupled system with Unity Container and MEF (Managed Extensibility Framework) using Inversion of Control. I’ll not be explaining much theory but rather focus more on practical implementations. For the readers who are following this series, they can use their existing solution that they have created till time. For my new readers of this article, I have provided the download link for the previous source code and current source code as well.

For theory and understanding of DI and IOC you can follow the following links: Unity and Inversion of Control(IOC).

Roadmap

Here is my roadmap for learning RESTful APIs,

Existing Design and Problem

We already have an existing design. If you open the solution, you’ll get to see the structure as mentioned below,

We tried to design a loosely coupled architecture in the following way,

DataModel (responsible for communication with database) : Only talks to service layer.
Services (acts as a business logic layer between REST endpoint and data access) : Communicates between REST endpoint and DataModel.
REST API i.e. Controllers: Only talks to services via the interfaces exposed.

But when we tried to resolve the dependency of UnitOfWork from Services, we had to reference

DataModel dll in to our WebAPI project; this violated our system like shown in following image,

In this article we’ll try to resolve dependency (data model) of a dependency (services) from our existing solution. My controller depended on services and my services depended on data model. Now we’ll design an architecture in which components will be independent of each other in terms of object creation and instantiation. To achieve this we’ll make use of MEF(Managed Extensibility Framework) along with Unity Container and reflection.

Image source : http://o5.com/wp-content/uploads/2010/08/dreamstime_15583711-550×371.jpg

Ideally, we should not be having the below code in our Bootstrapper class,

container.RegisterType().RegisterType(new HierarchicalLifetimeManager());

Managed Extensibility Framework (MEF)

You can have a read about Unity from msdn link. I am just quoting some lines from msdn,

“The Managed Extensibility Framework or MEF is a library for creating lightweight, extensible applications. It allows application developers to discover and use extensions with no configuration required. It also lets extension developers easily encapsulate code and avoid fragile hard dependencies. MEF not only allows extensions to be reused within applications, but across applications as well.”
“MEF is an integral part of the .NET Framework 4, and is available wherever the .NET Framework is used. You can use MEF in your client applications, whether they use Windows Forms, WPF, or any other technology, or in server applications that use ASP.NET.”

Creating a Dependency Resolver with Unity and MEF

Open your Visual studio, I am using VS 2010, you can use VS version 2010 or above. Load the solution.

Step 1: Right click solution explorer and add a new project named Resolver,

I have intentionally chosen this name, and you already know it why J

Step 2: Right click Resolver project and click on ManageNugetPackage, in the interface of adding new package, search Unity.MVC3 in online library,

Install the package to your solution.

Step 3: Right click resolver project and add a reference to System.ComponentModel.Composition.

You can find the dll into your GAC.I am using framework 4.0, so referring to the same version dll.

This DLL is the part of MEF and is already installed with .NET Framework 4.0 in the system GAC. This DLL provides classes that are very core of MEF.

Step 4: Just add an interface named IComponent to Resolver project that contains the initialization method named Setup. We’ll try to implement this interface into our Resolver class that we’ll create in our other projects like DataModel, Services and WebApI.

namespace Resolver
{
    /// <summary>
    /// Register underlying types with unity.
    /// </summary>
    public interface IComponent
    {
      
    }
}

Step 5: Before we declare our Setup method, just add one more interface responsible for serving as a contract to register types. I name this interface as IRegisterComponent,

namespace Resolver
{
    /// <summary>
    /// Responsible for registering types in unity configuration by implementing IComponent
    /// </summary>
    public interface IRegisterComponent
    {
        /// <summary>
        /// Register type method
        /// </summary>
        /// <typeparam name="TFrom"></typeparam>
        /// <typeparam name="TTo"></typeparam>
        /// <param name="withInterception"></param>
        void RegisterType(bool withInterception = false) where TTo : TFrom;
 
        /// <summary>
        /// Register type with container controlled life time manager
        /// </summary>
        /// <typeparam name="TFrom"></typeparam>
        /// <typeparam name="TTo"></typeparam>
        /// <param name="withInterception"></param>
        void RegisterTypeWithControlledLifeTime(bool withInterception = false) where TTo : TFrom;
    }
}

In this interface I have declared two methods, one RegisterType and other in to RegisterType with Controlled life time of the object, i.e. the life time of an object will be hierarchal in manner. This is kind of same like we do in Unity.

Step 6: Now declare Setup method on our previously created IComponent interface, that takes instance ofIRegisterComponent as a parameter,

void SetUp(IRegisterComponent registerComponent);

So our IComponent interface becomes,

namespace Resolver
{
    /// <summary>
    /// Register underlying types with unity.
    /// </summary>
    public interface IComponent
    {
        void SetUp(IRegisterComponent registerComponent);
    }
}

Step 6: Now we’ll write a packager or you can say a wrapper over MEF and Unity to register types/ components. This is the core MEF implementation. Create a class named ComponentLoader, and add following code to it,

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Practices.Unity;
using System.ComponentModel.Composition.Hosting;
using System.ComponentModel.Composition.Primitives;
using System.Reflection;
 
namespace Resolver
{
    public static class ComponentLoader
    {
        public static void LoadContainer(IUnityContainer container, string path, string pattern)
        {
            var dirCat = new DirectoryCatalog(path, pattern);
            var importDef = BuildImportDefinition();
            try
            {
                using (var aggregateCatalog = new AggregateCatalog())
                {
                    aggregateCatalog.Catalogs.Add(dirCat);
 
                    using (var componsitionContainer = new CompositionContainer(aggregateCatalog))
                    {
                        IEnumerable exports = componsitionContainer.GetExports(importDef);
 
                        IEnumerable modules =
                            exports.Select(export => export.Value as IComponent).Where(m => m != null);
 
                        var registerComponent = new RegisterComponent(container);
                        foreach (IComponent module in modules)
                        {
                            module.SetUp(registerComponent);
                        }
                    }
                }
            }
            catch (ReflectionTypeLoadException typeLoadException)
            {
                var builder = new StringBuilder();
                foreach (Exception loaderException in typeLoadException.LoaderExceptions)
                {
                    builder.AppendFormat("{0}\n", loaderException.Message);
                }
 
                throw new TypeLoadException(builder.ToString(), typeLoadException);
            }
        }
 
        private static ImportDefinition BuildImportDefinition()
        {
            return new ImportDefinition(
                def => true, typeof(IComponent).FullName, ImportCardinality.ZeroOrMore, false, false);
        }
    }
 
    internal class RegisterComponent : IRegisterComponent
    {
        private readonly IUnityContainer _container;
 
        public RegisterComponent(IUnityContainer container)
        {
            this._container = container;
            //Register interception behaviour if any
        }
 
        public void RegisterType(bool withInterception = false) where TTo : TFrom
        {
            if (withInterception)
            {
                //register with interception
            }
            else
            {
                this._container.RegisterType();
            }
        }
 
        public void RegisterTypeWithControlledLifeTime(bool withInterception = false) where TTo : TFrom
        {
            this._container.RegisterType(new ContainerControlledLifetimeManager());
        }
    }
}

Step 7: Now our Resolver wrapper is ready. Build the project and add its reference to DataModel, BusinessServices and WebApi project like shown below,

Setup Business Services

We already have added reference of Resolver in BusinessServices project. We agreed to implement IComponent interface in each of our project.

So create a class named DependencyResolver and implement IComponent interface into it, we make use of reflection too to import IComponent type. So add a class and add following code to that DependencyResolverclass,

using System.ComponentModel.Composition;
using DataModel;
using DataModel.UnitOfWork;
using Resolver;
 
namespace BusinessServices
{
    [Export(typeof(IComponent))]
    public class DependencyResolver : IComponent
    {
        public void SetUp(IRegisterComponent registerComponent)
        {
            registerComponent.RegisterType();
 
        }
    }
}

Note that we have implemented SetUp method and in the same method we registered type for my ProductService.

All of the existing code base remains same. We don’t need to touch the IProductServices interface or ProductServices class.

Setup DataModel

We have added Resolver project reference to DataModel project as well. So we’ll try to register the type of UnitOfWork in this project. We proceed in same fashion, just add a DependencyResolver class and implement its Setup method to register type of UnitOfWork. To make the code more readable and standard, I made a change.I just added an interface for UnitOfWork and named it IUnitOfWork. Now my UnitOfWork class derives from this, you can do this exercise in earlier versions of projects we discussed in first two articles.

So my IUnitOfWork contains declaration of a single public method in UnitOfWork,

namespace DataModel.UnitOfWork
{
    public interface IUnitOfWork
    {
        /// <summary>
        /// Save method.
        /// </summary>
        void Save();
    }
}

Now register the type for UnitOfWork in DepenencyResolver class, our class becomes as shown below,

using System.ComponentModel.Composition;
using System.Data.Entity;
using DataModel.UnitOfWork;
using Resolver;
 
namespace DataModel
{
    [Export(typeof(IComponent))]
    public class DependencyResolver : IComponent
    {
        public void SetUp(IRegisterComponent registerComponent)
        {
            registerComponent.RegisterType();
        }
    }
}

Again, no need to touch any existing code of this project.

Setup REST endpoint / WebAPI project

Our 90% of the job is done.

We now need to setup or WebAPI project. We’ll not add any DependencyResolver class in this project. We’ll invert the calling mechanism of layers in Bootstrapper class that we already have, so when you open your bootstrapper class, you’ll get the code something like,

using System.Web.Http;
using System.Web.Mvc;
using BusinessServices;
using DataModel.UnitOfWork;
using Microsoft.Practices.Unity;
using Unity.Mvc3;
 
namespace WebApi
{
    public static class Bootstrapper
    {
        public static void Initialise()
        {
            var container = BuildUnityContainer();
 
            DependencyResolver.SetResolver(new UnityDependencyResolver(container));
 
            // register dependency resolver for WebAPI RC
            GlobalConfiguration.Configuration.DependencyResolver = new Unity.WebApi.UnityDependencyResolver(container);
        }
 
        private static IUnityContainer BuildUnityContainer()
        {
            var container = new UnityContainer();
 
            // register all your components with the container here
            // it is NOT necessary to register your controllers
           
            // e.g. container.RegisterType();       
            container.RegisterType().RegisterType(new HierarchicalLifetimeManager());
 
            return container;
        }
    }
}

Now, we need to change the code base a bit to make our system loosely coupled.Just remove the reference of DataModel from WebAPI project.

We don’t want our DataModel to be exposed to WebAPI project, that was our aim though, so we cut down the dependency of DataModel project now.

Add following code of Bootstrapper class to the existing Bootstarpper class,

using System.Web.Http;
//using DataModel.UnitOfWork;
using Microsoft.Practices.Unity;
using Resolver;
using Unity.Mvc3;
 
namespace WebApi
{
    public static class Bootstrapper
    {
        public static void  Initialise()
        {
            var container = BuildUnityContainer();
 
            System.Web.Mvc.DependencyResolver.SetResolver(new UnityDependencyResolver(container));
 
            // register dependency resolver for WebAPI RC
            GlobalConfiguration.Configuration.DependencyResolver = new Unity.WebApi.UnityDependencyResolver(container);
        }
 
        private static IUnityContainer BuildUnityContainer()
        {
            var container = new UnityContainer();
 
            // register all your components with the container here
            // it is NOT necessary to register your controllers
           
            // e.g. container.RegisterType();       
           // container.RegisterType().RegisterType(new HierarchicalLifetimeManager());
 
            RegisterTypes(container);
 
            return container;
        }
 
        public static void RegisterTypes(IUnityContainer container)
        {
 
            //Component initialization via MEF
            ComponentLoader.LoadContainer(container, ".\\bin", "WebApi.dll");
            ComponentLoader.LoadContainer(container, ".\\bin", "BusinessServices.dll");
 
        }
    }
}

It is kind of redefining Bootstrapper class without touching our existing controller methods. We now don’t even have to register type for ProductServices as well, we already did this in BusinessServices project.

Note that in RegisterTypes method we load components/dlls through reflection making use of ComponentLoader.We wrote two lines, first to load WebAPI.dll and another one to load Business Services.dll.

Had the name of BusinessServicess.dll be WebAPI.Services.dll, then we would have only written one line of code to load both the WebAPI and BusinessService dll like shown below,

ComponentLoader.LoadContainer(container, ".\\bin", "WebApi*.dll");

Yes we can make use of Regex.

Running the application

Just run the application, we get,

We already have our test client added, but for new readers, just go to Manage Nuget Packages, by right clicking WebAPI project and type WebAPITestClient in searchbox in online packages,

You’ll get “A simple Test Client for ASP.NET Web API”, just add it. You’ll get a help controller in Areas-> HelpPage like shown below,

I have already provided the database scripts and data in my previous article, you can use the same.

Append “/help” in the application url, and you’ll get the test client,

Service for GetAllProduct,

For Create a new product,

In database, we get new product,

Update product:

We get in database,

Delete product:

In database:

Advantages of this design

In my earlier articles I focussed more on design flaws, but our current design have emerged with few added advantages,

We got an extensible and loosely coupled application design that can go far with more new components added in the same way.
Registering types automatically through reflection. Suppose we want to register any Interface implementation to our REST endpoint, we just need to load that dll in our Bootstrapper class, or if dll’s are of common suffix names then we just have to place that DLL in bin folder, and that will automatically be loaded at run time.
Image source: http://a.pragprog.com/magazines/2013-07/images/iStock_000021011143XSmall__1mfk9b__.jpg
Database transactions or any of such module is now not exposed to the service endpoint, this makes our service more secure and maintains the design structure too.

Conclusion

We now know how to use Unity container to resolve dependency and perform inversion of control using MEF too. In my next article I’ll try to explain how we can open multiple endpoints to our REST service and create custom url’s in the true REST fashion in my WebAPI. Till then Happy Coding Smile | :) You can also download the source code from GitHub. Add the required packages, if they are missing in the source code.

Other Series

My other series of articles:

For more technical articles you can reach out to CodeTeddy.

Download Source Code

RESTful Day #2: Inversion of control using dependency injection in Web API’s using Unity Container and Bootstrapper

Introduction

My article will explain how we can make our Web API service architecture loosely coupled and more flexible. We already learnt that how we can create a RESTful service using Asp.net Web API and Entity framework in my last article. If you remember we ended up in a solution with a design flaw, we’ll try to overcome that flaw by resolving the dependencies of dependent components. For those who have not followed my previous article, they can learn by having the sample project attached as a test application from my first article.

Image source : https://www.pehub.com/wp-content/uploads/2013/06/independent-300×200.jpg

There are various methods you can use to resolve dependency of components. In my article I’ll explain how to resolve dependency with the help of Unity Container provided by Microsoft’s Unity Application Block.

We’ll not go into very detailed theory, for theory and understanding of DI and IOC you can follow the following links: Unity and Inversion of Control(IOC). We’ll straight away jump into practical implementation.

Roadmap

Our roadmap for learning RESTful APIs remains same,

Existing Design and Problem

We already have an existing design. If you open the solution, you’ll get to see the structure as mentioned below,

The modules are dependent in a way,

There is no problem with the structure, but the way they interact to each other is really problematic. You must have noticed that we are trying to communicate with layers, making the physical objects of classes.

For e.g.

Controller constructor makes an object of Service layer to communicate,

        /// <summary>
        /// Public constructor to initialize product service instance
        /// </summary>
        public ProductController()
        {
            _productServices =new ProductServices();
        }

Service constructor, in turn, makes and object of UnitOfWork to communicate to database,

        /// <summary>
        /// Public constructor.
        /// </summary>
        public ProductServices()
        {
            _unitOfWork = new UnitOfWork();
        }

The problem lies in these code pieces. We see Controller is dependent upon instantiation of Service and Service is dependent upon UnitOfWork to get instantiated. Our Layers should not be that tightly coupled and should be dependent on each other.

The work of creating object should be assigned to someone else. Our layers should not worry about creating objects.

We’ll assign this role to a third party that will be called our container. Fortunately, Unity provides that help to us, to get rid of this dependency problem and invert the control flow by injecting dependency not by creating objects by new but through constructors or properties. There are other methods too, but I am not going into detail.

Introduction to Unity

You can have a read about Unity from this link; I am just quoting some lines,

Image source: http://img.tradeindia.com/fp/1/669/664.jpg

“The Unity Application Block (Unity) is a lightweight, extensible dependency injection container that supports constructor injection, property injection, and method call injection. It provides developers with the following advantages:

It provides simplified object creation, especially for hierarchical object structures and dependencies, which simplifies application code.
It supports abstraction of requirements; this allows developers to specify dependencies at run time or in configuration and simplify management of crosscutting concerns.
It increases flexibility by deferring component configuration to the container.
It has a service location capability; this allows clients to store or cache the container. This is especially useful in ASP.NET Web applications where developers can persist the container in the ASP.NET session or application.”

Setup Unity

Open your Visual studio, I am using VS 2010, You can use VS version 2010 or above. Load the solution.

Step 1: browse to Tools-> Library Packet Manager – > Packet manager Console,

We’ll add package for Unity Application Block.

In the left bottom corner of Visual Studio, You’ll find where to write the command.

Type command Unity.MVC3 and choose “WebApi” project before you fire the command.

Step 2: Bootstrapper class

Unity.MVC3 comes with a Bootstrapper class, as soon as you run the command, the Bootstrapper class will be generated in your solution->WebAPI project,

using System.Web.Http;
using System.Web.Mvc;
using BusinessServices;
using DataModel.UnitOfWork;
using Microsoft.Practices.Unity;
using Unity.Mvc3;

namespace WebApi
{
    public static class Bootstrapper
    {
        public static void Initialise()
        {
            var container = BuildUnityContainer();

            DependencyResolver.SetResolver(new UnityDependencyResolver(container));

            // register dependency resolver for WebAPI RC
            GlobalConfiguration.Configuration.DependencyResolver = new Unity.WebApi.UnityDependencyResolver(container);
        }

        private static IUnityContainer BuildUnityContainer()
        {
            var container = new UnityContainer();

            // register all your components with the container here
            // it is NOT necessary to register your controllers
            
            // e.g. container.RegisterType();        
            container.RegisterType().RegisterType(new HierarchicalLifetimeManager());

            return container;
        }
    }
}

This class comes with an initial configuration to setup your container. All the functionality is inbuilt, we only need to specify the dependencies that we need to resolve in the “BuildUnityContainer“, like it says in the commented statement,

            // register all your components with the container here
            // it is NOT necessary to register your controllers
            
            // e.g. container.RegisterType();

Step 3: Just specify the components below these commented lines that we need to resolve. In our case, it’sProductServices and UnitOfWork, so just add,

container.RegisterType().RegisterType(new HierarchicalLifetimeManager());

“HierarchicalLifetimeManager” maintains the lifetime of the object and child object depends upon parent object’s lifetime.

If you don’t find “UnitOfWork“, just add reference to DataModel project in WebAPI project.

So our Bootstrapper class becomes,

   public static class Bootstrapper
    {
        public static void Initialise()
        {
            var container = BuildUnityContainer();

            DependencyResolver.SetResolver(new UnityDependencyResolver(container));

            // register dependency resolver for WebAPI RC
            GlobalConfiguration.Configuration.DependencyResolver = new Unity.WebApi.UnityDependencyResolver(container);
        }

        private static IUnityContainer BuildUnityContainer()
        {
            var container = new UnityContainer();

            // register all your components with the container here
            // it is NOT necessary to register your controllers
            
            // e.g. container.RegisterType();        
            container.RegisterType().RegisterType(new HierarchicalLifetimeManager());

            return container;
        }

Like this we can also specify other dependent objects in BuildUnityContainerMethod.

Step 4: Now we need to call the Initialise method of Bootstrapper class. Note , we need the objects as soon as our modules load, therefore we require the container to do its work at the time of application load, therefore go to Global.asax file and add one line to call Initialise method, since this is a static method, we can directly call it using class name,

Bootstrapper.Initialise();

Our global.asax becomes,

using System.Linq;
using System.Web.Http;
using System.Web.Mvc;
using System.Web.Optimization;
using System.Web.Routing;
using Newtonsoft.Json;
using WebApi.App_Start;

namespace WebApi
{
    // Note: For instructions on enabling IIS6 or IIS7 classic mode, 
    // visit http://go.microsoft.com/?LinkId=9394801

    public class WebApiApplication : System.Web.HttpApplication
    {
        protected void Application_Start()
        {
            AreaRegistration.RegisterAllAreas();

            WebApiConfig.Register(GlobalConfiguration.Configuration);
            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            RouteConfig.RegisterRoutes(RouteTable.Routes);
            BundleConfig.RegisterBundles(BundleTable.Bundles);
            //Initialise Bootstrapper
            Bootstrapper.Initialise();

            //Define Formatters
            var formatters = GlobalConfiguration.Configuration.Formatters;
            var jsonFormatter = formatters.JsonFormatter;
            var settings = jsonFormatter.SerializerSettings;
            settings.Formatting = Formatting.Indented;
            // settings.ContractResolver = new CamelCasePropertyNamesContractResolver();
            var appXmlType = formatters.XmlFormatter.SupportedMediaTypes.FirstOrDefault(t => t.MediaType == "application/xml");
            formatters.XmlFormatter.SupportedMediaTypes.Remove(appXmlType);

            //Add CORS Handler
            GlobalConfiguration.Configuration.MessageHandlers.Add(new CorsHandler());
        }
    }
}

Half of the job is done. We now need to touchbase our controller and Service class constructors to utilize the instances already created for them at application load.

Setup Controller

We have already set up unity in our application. There are various methods in which we can inject dependency, like constructor injection, property injection, via service locator. I am here using Constructor Injection, because I find it best method to use with Unity Container to resolve dependency.

Just go to your ProductController, you find your constructor written as,

        /// <summary>
        /// Public constructor to initialize product service instance
        /// </summary>
        public ProductController()
        {
            _productServices =new ProductServices();
        }

Just add a parameter to your constructor that takes your ProductServices reference, like we did below

       /// <summary>
        /// Public constructor to initialize product service instance
        /// </summary>
        public ProductController(IProductServices productServices)
        {
            _productServices = productServices;
        }

And initialize your “productServices” variable with the parameter. In this case when the constructor of the controller is called, It will be served with pre-instantiated service instance, and does not need to create an instance of the service, our unity container did the job of object creation.

Setup Services

For services too, we proceed in a same fashion. Just open your ProductServices class, we see the dependency of UnitOfWork here as,

        /// <summary>
        /// Public constructor.
        /// </summary>
        public ProductServices()
        {
            _unitOfWork = new UnitOfWork();
        }

Again, we perform the same steps ,and pass a parameter of type UnitOfWork to our constructor,

Our code becomes,

        /// <summary>
        /// Public constructor.
        /// </summary>
        public ProductServices(UnitOfWork unitOfWork)
        {
            _unitOfWork = unitOfWork;
        }

Here also we’ll get the pre instantiated object on UnitOfWork. So service does need to worry about creating objects. Remember we did .RegisterType() in Bootstrapper class.

We have now made our components independent.

Image source: https://codeteddycom.files.wordpress.com/2015/05/d91c4-h1.jpg

Running the application

Our job is almost done.We need to run the application, Just hit F5. To our surprise we’ll end up in an error page,

Do you remember we added a test client to our project to test our API in my first article. That test client have a controller too, we need to override its settings to make our application work.Just go to Areas->HelpPage->Controllers->HelpController in WebAPI project like shown below,

Comment out the existing constructors and add a Configuration property like shown below,

      //Remove constructors and existing Configuration property.

        //public HelpController()
        //    : this(GlobalConfiguration.Configuration)
        //{
        //}

        //public HelpController(HttpConfiguration config)
        //{
        //    Configuration = config;
        //}

        //public HttpConfiguration Configuration { get; private set; }

        /// <summary>
        /// Add new Configuration Property
        /// </summary>
        protected static HttpConfiguration Configuration
        {
            get { return GlobalConfiguration.Configuration; }
        }

Our controller code becomes,

using System;
using System.Web.Http;
using System.Web.Mvc;
using WebApi.Areas.HelpPage.Models;

namespace WebApi.Areas.HelpPage.Controllers
{
    /// <summary>
    /// The controller that will handle requests for the help page.
    /// </summary>
    public class HelpController : Controller
    {
        //Remove constructors and existing Configuration property.

        //public HelpController()
        //    : this(GlobalConfiguration.Configuration)
        //{
        //}

        //public HelpController(HttpConfiguration config)
        //{
        //    Configuration = config;
        //}

        //public HttpConfiguration Configuration { get; private set; }

        /// <summary>
        /// Add new Configuration Property
        /// </summary>
        protected static HttpConfiguration Configuration
        {
            get { return GlobalConfiguration.Configuration; }
        }

        public ActionResult Index()
        {
            return View(Configuration.Services.GetApiExplorer().ApiDescriptions);
        }

        public ActionResult Api(string apiId)
        {
            if (!String.IsNullOrEmpty(apiId))
            {
                HelpPageApiModel apiModel = Configuration.GetHelpPageApiModel(apiId);
                if (apiModel != null)
                {
                    return View(apiModel);
                }
            }

            return View("Error");
        }
    }
}

Just run the application, we get,

We alreay have our test client added, but for new readers, I am just again explaining on how to add a test client to our API project.

Just go to Manage Nuget Packages, by right clicking WebAPI project and type WebAPITestClient in searchbox in online packages,

You’ll get “A simple Test Client for ASP.NET Web API”, just add it. You’ll get a help controller in Areas-> HelpPage like shown below,

I have already provided the database scripts and data in my previous article, you can use the same.

Append “/help” in the application url, and you’ll get the test client,

You can test each service by clicking on it.

Service for GetAllProduct,

For Create a new product,

In database, we get new product,

Update product:

We get in database,

Delete product:

In database:

Job done.

Image source: http://codeopinion.com/wp-content/uploads/2015/02/injection.jpg

Design Flaws

What if I say there are still flaws in this design, the design is still not loosely coupled.

Do you remember what we decided while writing our first application?

Our API talks to Services and Services talk to DataModel. We’ll never allow DataModel talk to APIs for security reasons. But did you notice that when we were registering the type in Bootstrapper class, we also registered the type of UnitOfWork that means we added DataModel as a reference to our API project. This is a design breach. We tried to resolve dependency of a dependency by violating our design and compromising security.

In my next article, we’ll overcome this situation, we’ll try to resolve dependency and its dependency without violating our design and compromising security. In fact we’ll make it more secure and loosely coupled.

In my next article we’ll make use of Managed Extensibility Framework(MEF) to achieve the same.

Conclusion

We now know how to use Unity container to resolve dependency and perform inversion of control.

But still there are some flaws in this design. In my next article, I’ll try to make the system more strong. Till then Happy Coding :-). You can also download the source code from GitHub. Add the required packages, if they are missing in the source code.

Other Series

My other series of articles:

For more technical articles you can reach out to CodeTeddy.

RESTful Day #1: Enterprise Level Application Architecture with Web API’s using Entity Framework, Generic Repository Pattern and Unit of Work

Download SourceCode from Github

Introduction

I have been practicing, reading a lot about RESTful services for past few days. To my surprise I could not find a complete series of practical implementations of ASP.NET Web API’s on the web. My effort in this series will be to focus on how we can develop basic enterprise level application architecture with Web API’s.

We’ll be discussing less theory and doing more practical to understand how RESTful services can be created using an ORM, we choose Entity Framework here. My first article in the series is to set up a basic architecture of REST service based application. Later on in my upcoming articles, I’ll explain how we can follow best standards to achieve enterprise level architecture.

Roadmap

My road for the series is as follows,

REST

Here is an extract from Wikipedia,

“Unlike SOAP-based web services, there is no “official” standard for RESTful web APIs. This is because REST is an architectural style, while SOAP is a protocol. Even though REST is not a standard per se, most RESTful implementations make use of standards such as HTTP, URI, JSON, and XML.“

I agree to it . Let’s do some coding.

Setup database

I am using SQL Server 2008 as a database server. I have provided the sql scripts to create the database in Sql Server, you can use the same to create one.I have given WebApiDb as my database name. My database contains three tables for now, Products, Tokens, User. In this tutorial we’ll only be dealing with product table to perform CURD operations using Web API and Entity framework. We’ll use Tokens and User in my upcoming article. For those who fail to create database through scripts, here is the structure you can follow,

Web API project

Open your Visual Studio, I am using VS 2010, You can use VS version 2010 or above.

Step 1: Create a new Project in your visual studio,

Step 2: There after choose to create ASP.NET MVC 4 Web application, and give it a name of your choice, I gave itWebAPI.

Step 3: Out of different type of project templates shown to you, choose Web API project,

Once done, you’ll get a project structure like shown below, with a default Home and Values controller.

You can choose to delete this ValuesController, as we’ll be using our own controller to learn.

Setup Data Access Layer

Let’s setup or data access layer first. We’ll be using Entity Framework 5.0 to talk to database. We’ll use Generic Repository Pattern and Unit of work pattern to standardize our layer.

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 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 and storing the data in the database.

Step 1 : Create a new class library in your visual studio, and name it DataModel as shown below,

Step2: In the same way, create one more project i.e. again a class library and call it BusinessEntities,

I’ll explain the use of this class library soon.

Step 3: Move on to your DataModel project , right click on it and add a new item, in the list shown, choose ADO.NET Data Model, and name it WebApiDataModel.edmx.

The file .edmx will contain the database information of our database that we created earlier, let’s set up this. You’ll be presented a wizard like follows,

Choose, generate from database. Choose Microsoft SQl Server like shown in the following image,

Click continue, then provide the credentials of your database, i.e. WebAPIdb, and connect it,

You’ll get a screen, showing the connection string of the database we chose,

Provide the name of the connection string as WebApiDbEntities and click Next.

Choose all the database objects, check all the check boxes, and provide a name for the model. I gave it a name WebApiDbModel.

Once you finish this wizard, you’ll get the schema ready in your datamodel project as follows,

We’ve got our schema in-place using Entity Framework. But few work is still remaining. We need our data context class and entities through which we’ll communicate with database.

So, moving on to next step.

Step 3: Click on tools in Visual Studio and open Extension manager. We need to get db context generator for our datamodel. We can also do it using default code generation item by right clicking in the edmx view and add code generation item, but that will generate object context class and that is heavier than db context. I want light weighted db context class to be created, so we’ll use extension manager to add a package and then create a db context class.

Search for Entity Framework Dbcontext generator in online gallery and select the one for EF 5.x like below,

I guess you need to restart Visual studio to get that into your templates.

Step 4 : Now right click in the .edmx file schema designer and choose “Add Code Generation Item..”.

Step 5 : Now you’ll see that we have got the template for the extension that we added, select that EF 5.x DbContext Generator and click Add.

After adding this we’ll get the db context class and its properties, this class is responsible for all database transactions that we need to perform, so our structure looks like as shown below,

Wow, we ended up in errors. But we got our db context class and our entity models, You can see them in our DataModel project. Errors? Nothing to worry about, it’s just we did not reference entity framework in our project. We’ll do it right away.

Step 6 : Go to Tools -> Library Packet Manager->Packet manager Console. You’ll get the console in left bottom of Visual studio.

Select dataModel project and write a command “Install-Package EntityFramework –Version 5.0.0” to install Entity Framework 5 in our DataModel project.

Press enter. And all the errors get resolved.

Generic Repository and Unit of Work

You can read about repository pattern and creating a repository in detail from my article :https://codeteddy.com/2013/09/03/learning-mvc-part-5repository-pattern-in-mvc3-application-with-entity-framework/.

Just to list down the benefits of Repository pattern,

It centralizes the data logic or Web service access logic.
It provides a substitution point for the unit tests.
It provides a flexible architecture that can be adapted as the overall design of the application evolves.

We’ll create a generic repository that works for all our entities. Creating repositories for each and every entity may result in lots of duplicate code in large projects.For creating Generic Repository you can follow : https://codeteddy.com/2013/09/03/learning-mvc-part-6-generic-repository-pattern-in-mvc3-application-with-entity-framework/

Step 1: Add a folder named GenericRepository in DataModel project and to that folder add a class named Generic Repository. Add following code to that class, that servers as a template based generic code for all the entities that will interact with database,

#region Using Namespaces...

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.Entity;
using System.Linq;

#endregion

namespace DataModel.GenericRepository
{
/// <summary>
    /// Generic Repository class for Entity Operations
    /// </summary>
    /// <typeparam name="TEntity"></typeparam>
    public class GenericRepository where TEntity : class
    {
#region Private member variables...
internal WebApiDbEntities Context;
internal DbSet DbSet;
#endregion

#region Public Constructor...
/// <summary>
        /// Public Constructor,initializes privately declared local variables.
        /// </summary>
        /// <param name="context"></param>
        public GenericRepository(WebApiDbEntities context)
        {
this.Context = context;
this.DbSet = context.Set();
        }
#endregion

#region Public member methods...

/// <summary>
        /// generic Get method for Entities
        /// </summary>
        /// <returns></returns>
        public virtual IEnumerable Get()
        {
            IQueryable query = DbSet;
return query.ToList();
        }

/// <summary>
        /// Generic get method on the basis of id for Entities.
        /// </summary>
        /// <param name="id"></param>
        /// <returns></returns>
        public virtual TEntity GetByID(object id)
        {
return DbSet.Find(id);
        }

/// <summary>
        /// generic Insert method for the entities
        /// </summary>
        /// <param name="entity"></param>
        public virtual void Insert(TEntity entity)
        {
            DbSet.Add(entity);
        }

/// <summary>
        /// Generic Delete method for the entities
        /// </summary>
        /// <param name="id"></param>
        public virtual void Delete(object id)
        {
            TEntity entityToDelete = DbSet.Find(id);
            Delete(entityToDelete);
        }

/// <summary>
        /// Generic Delete method for the entities
        /// </summary>
        /// <param name="entityToDelete"></param>
        public virtual void Delete(TEntity entityToDelete)
        {
if (Context.Entry(entityToDelete).State == EntityState.Detached)
            {
                DbSet.Attach(entityToDelete);
            }
            DbSet.Remove(entityToDelete);
        }

/// <summary>
        /// Generic update method for the entities
        /// </summary>
        /// <param name="entityToUpdate"></param>
        public virtual void Update(TEntity entityToUpdate)
        {
            DbSet.Attach(entityToUpdate);
            Context.Entry(entityToUpdate).State = EntityState.Modified;
        }

/// <summary>
        /// generic method to get many record on the basis of a condition.
        /// </summary>
        /// <param name="where"></param>
        /// <returns></returns>
        public virtual IEnumerable GetMany(Func<TEntity, bool> where)
        {
return DbSet.Where(where).ToList();
        }

/// <summary>
        /// generic method to get many record on the basis of a condition but query able.
        /// </summary>
        /// <param name="where"></param>
        /// <returns></returns>
        public virtual IQueryable GetManyQueryable(Func<TEntity, bool> where)
        {
return DbSet.Where(where).AsQueryable();
        }

/// <summary>
        /// generic get method , fetches data for the entities on the basis of condition.
        /// </summary>
        /// <param name="where"></param>
        /// <returns></returns>
        public TEntity Get(Func<TEntity, Boolean> where)
        {
return DbSet.Where(where).FirstOrDefault();
        }

/// <summary>
        /// generic delete method , deletes data for the entities on the basis of condition.
        /// </summary>
        /// <param name="where"></param>
        /// <returns></returns>
        public void Delete(Func<TEntity, Boolean> where)
        {
            IQueryable objects = DbSet.Where(where).AsQueryable();
foreach (TEntity obj in objects)
                DbSet.Remove(obj);
        }

/// <summary>
        /// generic method to fetch all the records from db
        /// </summary>
        /// <returns></returns>
        public virtual IEnumerable GetAll()
        {
return DbSet.ToList();
        }

/// <summary>
        /// Inclue multiple
        /// </summary>
        /// <param name="predicate"></param>
        /// <param name="include"></param>
        /// <returns></returns>
        public IQueryable GetWithInclude(
            System.Linq.Expressions.Expression<Func<TEntity, 
bool>> predicate, params string[] include)
        {
            IQueryable query = this.DbSet;
            query = include.Aggregate(query, (current, inc) => current.Include(inc));
return query.Where(predicate);
        }

/// <summary>
        /// Generic method to check if entity exists
        /// </summary>
        /// <param name="primaryKey"></param>
        /// <returns></returns>
        public bool Exists(object primaryKey)
        {
return DbSet.Find(primaryKey) != null;
        }

/// <summary>
        /// Gets a single record by the specified criteria (usually the unique identifier)
        /// </summary>
        /// <param name="predicate">Criteria to match on</param>
        /// <returns>A single record that matches the specified criteria</returns>
        public TEntity GetSingle(Func<TEntity, bool> predicate)
        {
return DbSet.Single(predicate);
        }

/// <summary>
        /// The first record matching the specified criteria
        /// </summary>
        /// <param name="predicate">Criteria to match on</param>
        /// <returns>A single record containing the first record matching the specified criteria</returns>
        public TEntity GetFirst(Func<TEntity, bool> predicate)
        {
return DbSet.First(predicate);
        }


#endregion
    }
}

Unit of Work

Again I’ll not explain in detail what Unit of Work is. You can google about the theory or follow my existing article on MVC with Unit of Work.

To give a heads up, again from my existing article, the important responsibilities of Unit of Work are,

To manage transactions.
To order the database inserts, deletes, and updates.
To prevent duplicate updates. Inside a single usage of a Unit of Work object, different parts of the code may mark the same Invoice object as changed, but the Unit of Work class will only issue a single UPDATE command to the database.

The value of using a Unit of Work pattern is to free the rest of our code from these concerns so that you can otherwise concentrate on business logic.

Step 1: Create a folder named UnitOfWork, add a class to that folder named UnitOfWork.cs,

Add GenericRepository properties for all the three entities that we got. The class also implementsIDisposableinterface and it’s method Dispose to free up connections and objects. The class will be as follows,

#region Using Namespaces...

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Data.Entity.Validation;
using DataModel.GenericRepository;

#endregion

namespace DataModel.UnitOfWork
{
/// <summary>
    /// Unit of Work class responsible for DB transactions
    /// </summary>
    public class UnitOfWork : IDisposable
    {
#region Private member variables...

private WebApiDbEntities _context = null;
private GenericRepository _userRepository;
private GenericRepository _productRepository;
private GenericRepository _tokenRepository;
#endregion

public UnitOfWork()
        {
            _context = new WebApiDbEntities();
        }

#region Public Repository Creation properties...

/// <summary>
        /// Get/Set Property for product repository.
        /// </summary>
        public GenericRepository ProductRepository
        {
get
            {
if (this._productRepository == null)
this._productRepository = new GenericRepository(_context);
return _productRepository;
            }
        }

/// <summary>
        /// Get/Set Property for user repository.
        /// </summary>
        public GenericRepository UserRepository
        {
get
            {
if (this._userRepository == null)
this._userRepository = new GenericRepository(_context);
return _userRepository;
            }
        }

/// <summary>
        /// Get/Set Property for token repository.
        /// </summary>
        public GenericRepository TokenRepository
        {
get
            {
if (this._tokenRepository == null)
this._tokenRepository = new GenericRepository(_context);
return _tokenRepository;
            }
        }
#endregion

#region Public member methods...
/// <summary>
        /// Save method.
        /// </summary>
        public void Save()
        {
try
            {
                _context.SaveChanges();
            }
catch (DbEntityValidationException e)
            {

var outputLines = new List<string>();
foreach (var eve in e.EntityValidationErrors)
                {
                    outputLines.Add(string.Format(
"{0}: Entity of type \"{1}\" in state \"{2}\" has the following validation errors:", DateTime.Now, 
                        eve.Entry.Entity.GetType().Name, eve.Entry.State));
foreach (var ve in eve.ValidationErrors)
                    {
                        outputLines.Add(string.Format("- Property: \"{0}\", Error: \"{1}\"", ve.PropertyName, ve.ErrorMessage));
                    }
                }
                System.IO.File.AppendAllLines(@"C:\errors.txt", outputLines);

throw e;
            }

        }

#endregion

#region Implementing IDiosposable...

#region private dispose variable declaration...
private bool disposed = false; 
#endregion

/// <summary>
        /// Protected Virtual Dispose method
        /// </summary>
        /// <param name="disposing"></param>
        protected virtual void Dispose(bool disposing)
        {
if (!this.disposed)
            {
if (disposing)
                {
                    Debug.WriteLine("UnitOfWork is being disposed");
                    _context.Dispose();
                }
            }
this.disposed = true;
        }

/// <summary>
        /// Dispose method
        /// </summary>
        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        } 
#endregion
    }
}

Now we have completely set up our data access layer, and our project structure looks like as shown below,

Setup Business Entities

Remember, we created a business entities project. You may wonder, we already have database entities to interact with database then why do we need Business Entities? The answer is as simple as that, we are trying to follow a proper structure of communication, and one would never want to expose the database entities to the end client, in our case is Web API, it involves lot of risk. Hackers may manipulate the details and get accessto your database.Instead we’ll use database entities in our business logic layer and use Business Entities as transfer objects to communicate between business logic and Web API project. So business entities may have different names but, their properties remains same as database entities. In our case we’ll add same name business entity classes appendint word “Entity” to them in our BusinessEntity project. So we’ll end up having three classes as follows,

Product entity

public class ProductEntity
    {
public int ProductId { get; set; }
public string ProductName { get; set; }
    }

Token entity

public class TokenEntity
    {
public int TokenId { get; set; }
public int UserId { get; set; }
public string AuthToken { get; set; }
public System.DateTime IssuedOn { get; set; }
public System.DateTime ExpiresOn { get; set; }
    }

User entity

public class UserEntity
    {
public int UserId { get; set; }
public string UserName { get; set; }
public string Password { get; set; }
public string Name { get; set; }
    }

Setup Business Services Project

Add a new class library to the solution named BusinessServices. This layer will act as our business logic layer. Note that, we can make use of our API controllers to write business logic, but I am trying to segregate my business logic in an extra layer so that if in future I want to use WCF, MVC, ASP.NET Web Pages or any other application as my presentation layer then I can easily integrate my Business logic layer in it.

We’ll make this layer testable, so we need to create an interface in and declare CURD operations that we need to perform over product table.Before we proceed, add the reference of BusinessEntities project and DataModel project to this newly created project

Step 1 : Create an interface named IProductServices and add following code to it for CURD operations methods,

using System.Collections.Generic;
using BusinessEntities;

namespace BusinessServices
{
/// <summary>
    /// Product Service Contract
    /// </summary>
    public interface IProductServices
    {
        ProductEntity GetProductById(int productId);
        IEnumerable GetAllProducts();
int CreateProduct(ProductEntity productEntity);
bool UpdateProduct(int productId,ProductEntity productEntity);
bool DeleteProduct(int productId);
    }
}

Step 2 : Create a class to implement this interface.name that class ProductServices,

The class contains a private variable of UnitOfWork and a constructor to initialize that variable,

private readonly UnitOfWork _unitOfWork;

/// <summary>
        /// Public constructor.
        /// </summary>
        public ProductServices()
        {
            _unitOfWork = new UnitOfWork();
        }

We have decided not to expose our db entities to Web API project, so we need something to map the db entities data to my business entity classes. We’ll make use of AutoMapper.You can read about AutoMapper in my this article.

Step 3: Just right click project-> Extension manager, search for AutoMapper in online galary and add to BusinessServices project,

Step 4: Implement methods in ProductServices class,

Add following code to the class,

using System.Collections.Generic;
using System.Linq;
using System.Transactions;
using AutoMapper;
using BusinessEntities;
using DataModel;
using DataModel.UnitOfWork;

namespace BusinessServices
{
/// <summary>
    /// Offers services for product specific CRUD operations
    /// </summary>
    public class ProductServices:IProductServices
    {
private readonly UnitOfWork _unitOfWork;

/// <summary>
        /// Public constructor.
        /// </summary>
        public ProductServices()
        {
            _unitOfWork = new UnitOfWork();
        }

/// <summary>
        /// Fetches product details by id
        /// </summary>
        /// <param name="productId"></param>
        /// <returns></returns>
        public BusinessEntities.ProductEntity GetProductById(int productId)
        {
var product = _unitOfWork.ProductRepository.GetByID(productId);
if (product != null)
            {
                Mapper.CreateMap();
var productModel = Mapper.Map(product);
return productModel;
            }
return null;
        }

/// <summary>
        /// Fetches all the products.
        /// </summary>
        /// <returns></returns>
        public IEnumerable GetAllProducts()
        {
var products = _unitOfWork.ProductRepository.GetAll().ToList();
if (products.Any())
            {
                Mapper.CreateMap();
var productsModel = Mapper.Map<List, List>(products);
return productsModel;
            }
return null;
        }

/// <summary>
        /// Creates a product
        /// </summary>
        /// <param name="productEntity"></param>
        /// <returns></returns>
        public int CreateProduct(BusinessEntities.ProductEntity productEntity)
        {
using (var scope = new TransactionScope())
            {
var product = new Product
                {
                    ProductName = productEntity.ProductName
                };
                _unitOfWork.ProductRepository.Insert(product);
                _unitOfWork.Save();
                scope.Complete();
return product.ProductId;
            }
        }

/// <summary>
        /// Updates a product
        /// </summary>
        /// <param name="productId"></param>
        /// <param name="productEntity"></param>
        /// <returns></returns>
        public bool UpdateProduct(int productId, BusinessEntities.ProductEntity productEntity)
        {
var success = false;
if (productEntity != null)
            {
using (var scope = new TransactionScope())
                {
var product = _unitOfWork.ProductRepository.GetByID(productId);
if (product != null)
                    {
                        product.ProductName = productEntity.ProductName;
                        _unitOfWork.ProductRepository.Update(product);
                        _unitOfWork.Save();
                        scope.Complete();
                        success = true;
                    }
                }
            }
return success;
        }

/// <summary>
        /// Deletes a particular product
        /// </summary>
        /// <param name="productId"></param>
        /// <returns></returns>
        public bool DeleteProduct(int productId)
        {
var success = false;
if (productId > 0)
            {
using (var scope = new TransactionScope())
                {
var product = _unitOfWork.ProductRepository.GetByID(productId);
if (product != null)
                    {

                        _unitOfWork.ProductRepository.Delete(product);
                        _unitOfWork.Save();
                        scope.Complete();
                        success = true;
                    }
                }
            }
return success;
        }
    }
}

Let me explain the idea of the code. We have 5 methods as follows,

To get product by id ( GetproductById ) : We call repository to get the product by id. Id comes as a parameter from the calling method to that service method. It returns the product entity from the database. Note that it will not return the exact db entity, instead we’ll map it with our business entity usingAutoMapper and return it to calling method.

/// <summary>
        /// Fetches product details by id
        /// </summary>
        /// <param name="productId"></param>
        /// <returns></returns>
        public BusinessEntities.ProductEntity GetProductById(int productId)
        {
var product = _unitOfWork.ProductRepository.GetByID(productId);
if (product != null)
            {
                Mapper.CreateMap();
var productModel = Mapper.Map(product);
return productModel;
            }
return null;
        }

Get all products from database (GetAllProducts) : This method returns all the products residing in database, again we make use of AutoMapper to map the list and return back.

/// <summary>
        /// Fetches all the products.
        /// </summary>
        /// <returns></returns>
        public IEnumerable GetAllProducts()
        {
var products = _unitOfWork.ProductRepository.GetAll().ToList();
if (products.Any())
            {
                Mapper.CreateMap();
var productsModel = Mapper.Map<List, List>(products);
return productsModel;
            }
return null;
        }

Create a new product (CreateProduct) : This method takes productBusinessEntity as an argument and creates a new object of actual database entity and insert it using unit of work.

/// <summary>
        /// Creates a product
        /// </summary>
        /// <param name="productEntity"></param>
        /// <returns></returns>
        public int CreateProduct(BusinessEntities.ProductEntity productEntity)
        {
using (var scope = new TransactionScope())
            {
var product = new Product
                {
                    ProductName = productEntity.ProductName
                };
                _unitOfWork.ProductRepository.Insert(product);
                _unitOfWork.Save();
                scope.Complete();
return product.ProductId;
            }
        }

I guess you can now write update and delete methods. So I am writing the code of complete class,

using System.Collections.Generic;
using System.Linq;
using System.Transactions;
using AutoMapper;
using BusinessEntities;
using DataModel;
using DataModel.UnitOfWork;

namespace BusinessServices
{
/// <summary>
    /// Offers services for product specific CRUD operations
    /// </summary>
    public class ProductServices:IProductServices
    {
private readonly UnitOfWork _unitOfWork;

/// <summary>
        /// Public constructor.
        /// </summary>
        public ProductServices()
        {
            _unitOfWork = new UnitOfWork();
        }

/// <summary>
        /// Fetches product details by id
        /// </summary>
        /// <param name="productId"></param>
        /// <returns></returns>
        public BusinessEntities.ProductEntity GetProductById(int productId)
        {
var product = _unitOfWork.ProductRepository.GetByID(productId);
if (product != null)
            {
                Mapper.CreateMap();
var productModel = Mapper.Map(product);
return productModel;
            }
return null;
        }

/// <summary>
        /// Fetches all the products.
        /// </summary>
        /// <returns></returns>
        public IEnumerable GetAllProducts()
        {
var products = _unitOfWork.ProductRepository.GetAll().ToList();
if (products.Any())
            {
                Mapper.CreateMap();
var productsModel = Mapper.Map<List, List>(products);
return productsModel;
            }
return null;
        }

/// <summary>
        /// Creates a product
        /// </summary>
        /// <param name="productEntity"></param>
        /// <returns></returns>
        public int CreateProduct(BusinessEntities.ProductEntity productEntity)
        {
using (var scope = new TransactionScope())
            {
var product = new Product
                {
                    ProductName = productEntity.ProductName
                };
                _unitOfWork.ProductRepository.Insert(product);
                _unitOfWork.Save();
                scope.Complete();
return product.ProductId;
            }
        }

/// <summary>
        /// Updates a product
        /// </summary>
        /// <param name="productId"></param>
        /// <param name="productEntity"></param>
        /// <returns></returns>
        public bool UpdateProduct(int productId, BusinessEntities.ProductEntity productEntity)
        {
var success = false;
if (productEntity != null)
            {
using (var scope = new TransactionScope())
                {
var product = _unitOfWork.ProductRepository.GetByID(productId);
if (product != null)
                    {
                        product.ProductName = productEntity.ProductName;
                        _unitOfWork.ProductRepository.Update(product);
                        _unitOfWork.Save();
                        scope.Complete();
                        success = true;
                    }
                }
            }
return success;
        }

/// <summary>
        /// Deletes a particular product
        /// </summary>
        /// <param name="productId"></param>
        /// <returns></returns>
        public bool DeleteProduct(int productId)
        {
var success = false;
if (productId > 0)
            {
using (var scope = new TransactionScope())
                {
var product = _unitOfWork.ProductRepository.GetByID(productId);
if (product != null)
                    {

                        _unitOfWork.ProductRepository.Delete(product);
                        _unitOfWork.Save();
                        scope.Complete();
                        success = true;
                    }
                }
            }
return success;
        }
    }
}

Job done at business service level. Let’s move on to API controller to call these methods.

Setup WebAPI project

Step1 : Just add the reference of BusinessEntity and BusinessService in the WebAPI project, our architecture becomes like this,

Step 2: Add a new WebAPI controller in Controller folder. Right click Controller folder and add a new controller.

We get a controller as follows,

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;

namespace WebApi.Controllers
{
public class ProductController : ApiController
    {
// GET api/product
        public IEnumerable<string> Get()
        {
return new string[] { "value1", "value2" };
        }

// GET api/product/5
        public string Get(int id)
        {
return "value";
        }

// POST api/product
        public void Post([FromBody]string value)
        {
        }

// PUT api/product/5
        public void Put(int id, [FromBody]string value)
        {
        }

// DELETE api/product/5
        public void Delete(int id)
        {
        }
    }
}

We get HTTP VERBS as method names. Web API is smart enough to recognize request with the name of the VERB itself. In our case we are doing CRUD operations, so we don’t need to change the names of the method, we just needed this. We only have to write calling logic inside these methods. In my upcoming articles of the series, we will figure out how we can define new routes and provide method names of our choice with those routes.

Step 3: Add logic to call Business Service methods, just make an object of Business Service and call its respective methods, our Controller class becomes like,

using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using BusinessEntities;
using BusinessServices;

namespace WebApi.Controllers
{
public class ProductController : ApiController
    {

private readonly IProductServices _productServices;

#region Public Constructor

/// <summary>
        /// Public constructor to initialize product service instance
        /// </summary>
        public ProductController()
        {
            _productServices =new ProductServices();
        }

#endregion

// GET api/product
        public HttpResponseMessage Get()
        {
var products = _productServices.GetAllProducts();
if (products != null)
            {
var productEntities = products as List ?? products.ToList();
if (productEntities.Any())
return Request.CreateResponse(HttpStatusCode.OK, productEntities);
            }
return Request.CreateErrorResponse(HttpStatusCode.NotFound, "Products not found");
        }

// GET api/product/5
        public HttpResponseMessage Get(int id)
        {
var product = _productServices.GetProductById(id);
if (product != null)
return Request.CreateResponse(HttpStatusCode.OK, product);
return Request.CreateErrorResponse(HttpStatusCode.NotFound, "No product found for this id");
        }

// POST api/product
        public int Post([FromBody] ProductEntity productEntity)
        {
return _productServices.CreateProduct(productEntity);
        }

// PUT api/product/5
        public bool Put(int id, [FromBody]ProductEntity productEntity)
        {
if (id  > 0)
            {
return _productServices.UpdateProduct(id, productEntity);
            }
return false;
        }

// DELETE api/product/5
        public bool Delete(int id)
        {
if (id > 0)
return _productServices.DeleteProduct(id);
return false;
        }
    }
}

Just run the application, we get,

But now how do we test our API? We don’t have client. Guys, we’ll not be writing a client now to test it.We’ll add a package that will do all our work.

Just go to Manage Nuget Packages, by right clicking WebAPI project and type WebAPITestClient in searchbox in online packages,

You’ll get “A simple Test Client for ASP.NET Web API”, just add it. You’ll get a help controller in Areas-> HelpPage like shown below,

Running the Application

Before running the application, I have put some test data in our product table.

Just hit F5, you get the same page as you got earlier, just append “/help” in its url, and you’ll get the test client,

You can test each service by clicking on it.

Service for GetAllProduct,

For Create a new product,

In database, we get new product,

Update product:

We get in database,

Delete product:

In database:

Job done.

Design Flaws

Architecture is tightly coupled. IOC (Inversion of Control) needs to be there.
We cannot define our own routes.
No exception handling and logging.
No unit tetsts.

Conclusion

We now know how to create a WebAPI and perform CRUD operations using n layered architecture.

But still there are some flaws in this design.In my next two articles I’ll explain how to make the system loosely coupled using Dependency Injection Principle. We’ll also cover all the design flaws to make our design better and stronger. Till then Happy Coding J You can also download the source code from GitHub.

Other Series

My other series of articles:

For more technical articles you can reach out to CodeTeddy.

Introduction

Roadmap

Request Logging

Setup NLog in WebAPI

Step 1: Download NLog Package

Step 2: Configuring NLog

NLogger Class

Adding Action Filter

Step 1: Adding LoggingFilterAttribute class

Step 2: Registering Action Filter (LoggingFilterAttribute)

Running the application

Exception Logging

Implementing Exception logging

Step 1: Exception Filter Attribute

Step 2: Modify NLogger Class

Step 3: Modify Controller for Exception

Step 4: Run the application

Custom Exception logging

Step 1: Add Custom Exception Classes

JSon Serializers

Modify NLogger Class

Modify GlobalExceptionAttribute

Modify Product Controller

Run the application

Update the controller for new Exception Handling

Product Controller

Conclusion

Read more:

Other Series

Introduction

Read more:

Other Series

Introduction

Roadmap

Existing Design and Problem

Introduction to Unity

Setup Unity

Setup Controller

Setup Services

Running the application

Design Flaws

Conclusion

Read more:

Other Series

Introduction

Roadmap

REST

Setup database

Web API project

Setup Data Access Layer

Generic Repository and Unit of Work

Unit of Work

Setup Business Entities

Product entity

Token entity

User entity

Setup Business Services Project

Setup WebAPI project

Running the Application

Design Flaws

Conclusion

Read more:

Other Series