Implementing repository for EF4 using DDD and IoC

Question

I think I\'m going in circles.

I\'m working on an MVC 3 solution using EF4 & POCOs (database-first) and IoC. My repository and UoW patterns were mostly adopted

Answer 1

This is subjective/matter of opinion, but you could make your Repository return IQueryable, then you can do your "complex queries" in your service like this:

return _repository // IRepository
          .Find() // IQueryable
          .Where(someComplexPredicate) // IQueryable
          .SingleOrDefault(); // T

ObjectSet : IQueryable, which makes this possible.

If you want to start doing ObjectSet-specific things in your service, you've got two options:

1. Expose the ObjectSet-specific method as a method on your Repository interface
2. Use an IQueryable extension method to do a "soft cast" to ObjectSet (e.g var objSet = source as ObjectSet).

Always try and go with option 1.

Perfect example is eager loading. There is a method called Include on the ObjectContext, so if you use IQuerayable in your Repository, how do you eager load?

Since Include takes a "magic string", you could accept this in your Find method on your Repository, e.g:

return _repository // IRepository
          .Find("Product.Orders") // IQueryable
          .Where(someComplexPredicate) // IQueryable
          .SingleOrDefault(); // T

Fortunately in EF CTP5 they have introduced a strongly-typed Include which works off IQueryable, so i didn't have to do the above when i cutover.

So as i said, best thing to do is expose methods on your Repository interface. But there needs to be a tradeoff - an interface should be a "contract" or "definition" of a service, not about the implmentation. So EF-specific things should be done via extension methods. General things can be done via the repository interface.