MEF with WCF – Start Up

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Introduction

In this article, I would be creating a Data Access Layer using WCF. I would be using MEF to Export the Data from Data Access Layer class and then Import it.

MEF offers a nice way to create Composable apps where I can so easily Import and Export Data.

Create an ADO.NET Entity Data Model as shown in the diagram below:

Create a new WCF Service as shown below:

Two files would be added to the solution as DataService and IDataService.cs.

Add a method GetArticles() to IDataService.cs.

[ServiceContract]
public interface IDataService
{
    [OperationContract]
    IEnumerable GetArticles();
}

Implement the method in DataService.cs:

public IEnumerable GetArticles()
     {
         PublishingCompanyEntities context = new PublishingCompanyEntities();
         var article = from art in context.Articles
                       select art.Title;

         return article;
     }

Creating a Data Class

1. Create a class named as Data.
   C#

   class Data
       {
   
       }

2. Add a property named as Articles.
   C#

   class Data
       {
           public IEnumerable Articles { get; set; }
       }

3. Add the Method GetData(). Call the method GetArticles() of DataService.
   C#

   class Data
       {
           public IEnumerable Articles { get; set; }
   
           public  IEnumerable GetData()
           {
              DataService ds = new DataService();
              return  Articles =  ds.GetArticles();
           }
       }

4. Add the Export attribute on the property Articles.
   C#

   class Data
       {
           [Export]
           public IEnumerable Articles { get; set; }
   
           public  IEnumerable GetData()
           {
              DataService ds = new DataService();
              return  ds.GetArticles();
           }
       }

5. Also add an Export attribute on the Data Class.
   C#

   [Export]
       class Data
       {
           [Export]
           public IEnumerable Articles { get; set; }
   
           public  IEnumerable GetData()
           {
              DataService ds = new DataService();
              return   ds.GetArticles();
           }
       }

6. I need to set the value of Articles property. I will do that in the constructor of Data class. So here is my final class:
   C#

   [Export]
       class Data
       {
           public Data()
           {
               Articles = GetData();
           }
   
           [Export]
           public IEnumerable Articles { get; set; }
   
           public  IEnumerable GetData()
           {
              DataService ds = new DataService();
              return  Articles =  ds.GetArticles();
           }
       }

Creating Another Class App

1. Create a class App.
   C#

   class App
       {
       }

2. Add a method Run() and put the code to compose the container.
   C#

   class App
       {
           public void Run()
           {
               var catalog = new AssemblyCatalog
      (System.Reflection.Assembly.GetExecutingAssembly());
   
               var container = new CompositionContainer(catalog);
               container.ComposeParts(this);
   
           }
       }

3. Create a property Articles and this time add an import attribute.
   C#

   class App
       {
           [Import]
           public IEnumerable Articles { get; set;}
   
           public void Run()
           {
               var catalog = new AssemblyCatalog
      (System.Reflection.Assembly.GetExecutingAssembly());
   
               var container = new CompositionContainer(catalog);
               container.ComposeParts(this);
           }
       }

4. Create an object for the Data Class and Import it.
   C#

   class App
       {
           [Import]
           public IEnumerable Articles { get; set;}
   
           [Import]
           Data data;
   
           public void Run()
           {
               var catalog = new AssemblyCatalog
      (System.Reflection.Assembly.GetExecutingAssembly());
   
               var container = new CompositionContainer(catalog);
               container.ComposeParts(this);
           }
       }

5. Add a foreach through the articles.
   C#

   class App
       {
           [Import]
           public IEnumerable Articles { get; set;}
   
           [Import]
           Data data;
   
           public void Run()
           {
               var catalog = new AssemblyCatalog
      (System.Reflection.Assembly.GetExecutingAssembly());
   
               var container = new CompositionContainer(catalog);
               container.ComposeParts(this);
   
   
               foreach (string art in Articles)
               {
                   Console.WriteLine(art);
               }
           }
       }

Please note that adding Export and Import attributes would need you to include the System.ComponentModel.Composition.

Call the App class now.

static void Main(string[] args)
     {
       App a = new App();
       a.Run();
       Console.ReadKey();
     }

It works! Happy coding.

History

• 23^rd July, 2011: Initial version