MEF With WCF - Start UP

In this article I will be creating a Data Access Layer using WCF. I will be using MEF to export the data from the Data Access Layer class and then import it.

MEF offers a nice way to create Composable applications where I can easily import and export data.

Created a ADO.Net Entity Data Model as shown in 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
   
   class Data
   {
   }
   
   
2. Add a property named Articles.
   
   class Data
   {
       public IEnumerable Articles { get; set; }
   }
   
   
3. Add the Method GetData(). Call the method GetArticles() of DataService .
   
   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.
   
   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.
   
   [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 the Articles Property. I will do that in the Contructor of the Data Class. So here is my final class.
   
   [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.
   
   class App
   {
   }
   
   
2. Add a method Run() and put the code to compose the container.
   
   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
   
   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.
   
   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 to iterate through the articles.
   
   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 to add the Export and Import attributes you need to add a reference to 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.