ARTICLE

MEF With WCF - Start UP

Posted by Mahadesh Mahalingappa Articles | WCF with C# July 23, 2011
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.
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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:

WCF1.gif

Create a new WCF Service as shown below:

WCF2.gif

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.

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