Why does my WCF Service not use my Entity Model?

Question

I got a problem on using WCF service and Entity Model with together. I have created an Entity Model from my existing database. This can be shown below;

There isn't any problem while using my classes in any console applicaton coming from "Entity Object Code Generator".

Then, I created WCF Service with Interface Below:

    [ServiceContract]
public interface IAuthorServices
{
    [OperationContract]
    [WebGet( UriTemplate="GetNews")]
    List<Newspaper> GetNews();

    [OperationContract]
    [WebGet(BodyStyle = WebMessageBodyStyle.Bare, RequestFormat = WebMessageFormat.Json, ResponseFormat = WebMessageFormat.Json, UriTemplate = "GetAuthors")]
    List<Author> GetAuthors();

    [OperationContract]
    [WebGet(BodyStyle = WebMessageBodyStyle.Bare, RequestFormat = WebMessageFormat.Json, ResponseFormat = WebMessageFormat.Json, UriTemplate = "GetAuthorTexts")]
    List<AuthorText> GetAuthorTexts();

    [OperationContract]
    [WebGet(BodyStyle = WebMessageBodyStyle.Bare, RequestFormat = WebMessageFormat.Json, ResponseFormat = WebMessageFormat.Json, UriTemplate = "GetTodaysTexts")]
    List<AuthorText> GetTodaysTexts();

    [OperationContract]
    [WebGet(BodyStyle = WebMessageBodyStyle.Bare, RequestFormat = WebMessageFormat.Json, ResponseFormat = WebMessageFormat.Json, UriTemplate = "GetExceptions")]
    List<KoseYazilari.Exception> GetExceptions();

}

However when I implement these methods in a service class and run my client application, I got an error like

How can I get rid of this problem?

Regards, KEMAL

Answer 1

Are your entities marked with a DataContract attribute? Are you making sure that they are serializable?

EDIT: By looking at your code it seems that you are using your entities directly. This is not a good practice because (even if your code was working) I don't think you want extra properties like the ones that Entity Framework auto-generates.

In these case you should consider to use DTOs (Data Transfer Objects), this is an example of how Newspaper class could be:

[DataContract]
public class NewspaperDTO
{
    public NewspaperDTO(Newspaper newspaper)
    {
        this.Name = newspaper.Name;
        this.Image = newspaper.Image;
        this.Link = newspaper.Link;
        this.Encoding = newspaper.Encoding;
    }

    [DataMember]
    public string Name { get; set; }

    [DataMember]
    public string Image { get; set; }

    [DataMember]
    public string Link { get; set; }

    [DataMember]
    public string Encoding { get; set; }
}

And then in your service:

public List<NewspaperDTO> GetNews()
{
    return entities.Newspapers.Select(a => new NewspaperDTO(a)).ToList();
}

P. S. I have noticed that your entities are not disposed (inside the WCF service I mean). You should consider using a pattern like this in every method of your service:

public List<NewspaperDTO> GetNews()
{
    using (var entities = new MyEntities())
    {
        return entities.Newspapers.Select(a => new NewspaperDTO(a)).ToList();
    }
}