Repository & Unit of Work Pattern for Entity Framework using Dependency Injection

Question

I tried the T4-Template from http://efrepository.codeplex.com, but I\'m struggling with the DI (uses StructureMap) Example code. It\'s just not enough for a DI beginner like me.

Answer 1

I normally use the following setup with EF end Structure map: (brace yourself, bunch o' code coming up).

This is the base interface we'll use to inject our controllers:

public interface ISession : IDisposable
{
    void CommitChanges();
    void Delete<T>(Expression<Func<T, bool>> expression) where T : class, new();
    void Delete<T>(T item) where T : class, new();
    void DeleteAll<T>() where T : class, new();
    T Single<T>(Expression<Func<T, bool>> expression) where T : class, new();
    IQueryable<T> All<T>() where T : class, new();
    void Add<T>(T item) where T : class, new();
    void Add<T>(IEnumerable<T> items) where T : class, new();
    void Update<T>(T item) where T : class, new();
}

And here an ISession implementation with EF in mind:

public class EntityFrameworkSession : ISession 
{
    // MyContext is a class inheriting from EF's DbContext
    readonly DbContext _context;

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

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

    public void Delete<T>(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>(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();
    }

    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);
        }
    }
    public void Update<T>(T item) where T : class, new()
    {
        //nothing needed here
    }
}

Now this ISession implementation is not very handy to inject because, while being nice and generic, it doesn't have a default constructor, so the way to solve it is by writing a small wrapper that only exposes a parameter-less constructor:

/// <summary>
/// This is the EF site alternative
/// </summary>
public class SiteEFSession : EntityFrameworkSession
{
    public SiteEFSession() : base(new MyContext())
    { }
}

Now we can easily inject it. We set it up in StructureMap as follows:

ObjectFactory.Initialize(x =>
{
    x.For<ISession>().Use<SiteEFSession>();
});

And if you have, for instance, an MVC style controller:

public class HomeController : Controller
{
   private readonly ISession _session;

   // ISession will be injected automatically
   public HomeController(ISession session)
   {
       _session = session;
   }
}

There you go. It's a helluva lot of code but you can pretty much copy/paste it into your solution and you should be good to go.