Entity Framework's NHibernate session.Load

public static class Helpers
{

    public static Ent LoadStub<Ent>(this DbContext db, object id) where Ent : class
    {
        string primaryKeyName = typeof(Ent).Name + "Id";
        return db.LoadStub<Ent>(primaryKeyName, id);
    }

    public static Ent LoadStub<Ent>(this DbContext db, string primaryKeyName, object id) where Ent: class
    {
        var cachedEnt = 
            db.ChangeTracker.Entries().Where(x => ObjectContext.GetObjectType(x.Entity.GetType()) == typeof(Ent)).SingleOrDefault(x =>
            {
                var entType = x.Entity.GetType();
                var value = entType.InvokeMember(primaryKeyName, System.Reflection.BindingFlags.GetProperty, null, x.Entity, new object[] { });

                return value.Equals(id);
            });

        if (cachedEnt != null)
        {
            return (Ent) cachedEnt.Entity;
        }
        else
        {
            Ent stub = (Ent) Activator.CreateInstance(typeof(Ent));

            
            typeof(Ent).InvokeMember(primaryKeyName, System.Reflection.BindingFlags.SetProperty, null, stub, new object[] { id });


            db.Entry(stub).State = EntityState.Unchanged;

            return stub;
        }

    }
}

So instead of using this pattern:

movie.Genres = movie.Genres ?? new List<Genre>();
movie.Genres.Clear();
foreach (int g in input.SelectedGenres)
{
    DbEntityEntry<Genre> cachedGenre = db.ChangeTracker.Entries<Genre>().SingleOrDefault(x => x.Entity.GenreId == g);

    Genre gx = null;
    if (cachedGenre != null)
        gx = cachedGenre.Entity;
    else
    {
        gx = new Genre { GenreId = g };
        db.Entry(gx).State = EntityState.Unchanged;
    }

    movie.Genres.Add(gx);
                       
}

We could now use this:

movie.Genres = movie.Genres ?? new List<Genre>();
movie.Genres.Clear();
foreach (int g in input.SelectedGenres)
    movie.Genres.Add(db.LoadStub<Genre>(g));

Sample use: http://www.ienablemuch.com/2011/07/using-checkbox-list-on-aspnet-mvc-with_16.html