How can I implement CRUD operations in a base class for an entity framework app?

Question

I'm working a simple EF/MVC app and I'm trying to implement some Repositories to handle my entities. I've set up a BaseObject Class and a IBaseRepository Interface to handle the most basic operations so I don't have to repeat myself each time:

public abstract class BaseObject<T>
    {
        public XA.Model.Entities.XAEntities db;
        public BaseObject()
        {
            db = new Entities.XAEntities();
        }

        public BaseObject(Entities.XAEntities cont)
        {
            db = cont;
        }

        public void Delete(T entity)
        {
            db.DeleteObject(entity);
            db.SaveChanges();
        }

        public void Update(T entity)
        {
            db.AcceptAllChanges();
            db.SaveChanges();
        }
   }

    public interface IBaseRepository<T>
    {
        void Add(T entity);

        T GetById(int id);
        IQueryable<T> GetAll();
    }

But then I find myself having to implement 3 basic methods in every Repository ( Add, GetById & GetAll):

public class AgencyRepository : Framework.BaseObject<Agency>, Framework.IBaseRepository<Agency>
    {
        public void Add(Agency entity)
        {
            db.Companies.AddObject(entity);
            db.SaveChanges();
        }
        public Agency GetById(int id)
        {
            return db.Companies.OfType<Agency>().FirstOrDefault(x => x.Id == id);
        }
        public IQueryable<Agency> GetAll()
        {
            var agn = from a in db.Companies.OfType<Agency>()
                      select a;
            return agn;
        }
    }

How can I get these into my BaseObject Class so I won't run in conflict with DRY.

Answer 1

Unless your base class is able to implement the interface (and then you can inherit it's implementation) you're prety much stuck writing them each time. If the steps are different for each child, then your not repeating yourself, even though it kinda feels like it.

As an off topic remark, rather than creating the db object in your base constructor, you may be able to save your self some pain down the road and dependency inject it instead. It will make your repository easier to unit test if your putting any code in there that's worthy of testing.

Answer 2

You can easily do this with T4 in EF 4. With more work, you can do it with T4 in EF 1.

But I recommend that you don't. MyEntity.Update() will be a fiction. The EF doesn't allow you to save part of the changes to a context (like one specific object). So your method will do something very different than it appears to do. IMHO this design is working against the EF. It also makes your entities persistence-aware by design.