Question about Interfaces and DI?

Question

I am using the Service/Repository/EF/POCO pattern in a MVC app, and had a couple questions about the Interfaces.

1) Should I make an Interface per Service? 2) Should I make an Interface per Repository?

Or, should I have a generic interface per layer (IService(Of T), IRepository(Of T)).

What I dont understand is how in the controller say, it takes a IService(Of Category) interface in it's constructor, how do I implements the methods in the concrete class?

Public Class HomeController
    Inherits System.Web.Mvc.Controller

    Private _Service As IService(Of Category)

    Public Sub New(ByVal Service As IService(Of Category))
        _Service = Service

    End Sub

    Function Index() As ActionResult

        Return View()
    End Function

End Class

The _Service does not have the methods of my concrete CategoryService class?

Make any sense?

score 1 · Accepted Answer · answered Mar 04 '11 at 18:59

1

Use concrete interface for service. If your services can be described by generic interface you most probably don't need them at all. Generic interface is often used for repositories because repositories usually offer same core methods.

answered Mar 04 '11 at 18:59

Ladislav Mrnka

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Thanks! Would you describe those interfaces in the Service Layer or in my case, I am describing my repository interface in MyProject.Core.dll? – Sam Mar 04 '11 at 19:28
@Sam: I probably don't understand your question. Are you asking where should you put these interfaces? – Ladislav Mrnka Mar 04 '11 at 19:31
Yes, where should I put them at? Should I put Repository Interfaces in the Repository layer, and Service Interfaces in the Service Layer, or should I put them all into one area, like a MyProject.Core area? - Thanks! – Sam Mar 04 '11 at 20:59
@Sam: It is just up to you. You can define them in the core assembly as well as in the assembly where implementation is defined. The first solution allow you easily replace implementation with other assembly but that is something which you most probably non need. – Ladislav Mrnka Mar 05 '11 at 08:44

score 0 · Answer 2 · answered Mar 04 '11 at 21:44

For myself, I use a generic session object that is strongly type, this class is in my domain project witch contains all my domain classes. You should take a look at this post : http://weblogs.asp.net/scottgu/archive/2010/07/16/code-first-development-with-entity-framework-4.aspx using Code-First approach.

Hope it helps!

Here my code for my Session class :

public class EFSession : ISession
{
    DbContext _context;

    public EFSession(DbContext context)
    {
        _context = context;
    }


    public void CommitChanges()
    {
        _context.SaveChanges();
    }

    public void Delete<T>(System.Linq.Expressions.Expression<Func<T, bool>> expression) where T : class, new()
    {

        var query = All<T>().Where(expression);
        foreach (var item in query)
        {
            Delete(item);
        }
    }

    public void Delete<T>(T item) where T : class, new()
    {
        _context.Set<T>().Remove(item);
    }

    public void DeleteAll<T>() where T : class, new()
    {
        var query = All<T>();
        foreach (var item in query)
        {
            Delete(item);
        }
    }

    public void Dispose()
    {
        _context.Dispose();
    }

    public T Single<T>(System.Linq.Expressions.Expression<Func<T, bool>> expression) where T : class, new()
    {
        return All<T>().FirstOrDefault(expression);
    }

    public IQueryable<T> All<T>() where T : class, new()
    {
        return _context.Set<T>().AsQueryable<T>();
    }

    public void Add<T>(T item) where T : class, new()
    {
        _context.Set<T>().Add(item);
    }

    public void Add<T>(IEnumerable<T> items) where T : class, new()
    {
        foreach (var item in items)
        {
            Add(item);
        }
    }

    /// <summary>
    /// Do not use this since we use EF4, just call CommitChanges() it does not do anything
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="item"></param>
    public void Update<T>(T item) where T : class, new()
    {
        //nothing needed here
    }
}

Question about Interfaces and DI?

2 Answers2

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