Should repositories implement IQueryable<T>?

Question

I'm considering one of two IRepository interfaces, one that is a descendant of IQueryable and one that contains IQueryable.

Like this:

public interface IRepository<T> : IQueryable<T> {     T Save(T entity);     void Delete(T entity); } 

Or this:

public interface IRepository<T> {     T Save(T entity);     void Delete(T entity);     IQueryable<T> Query(); } 

LINQ usage would be:

from dos in ServiceLocator.Current.GetInstance<IRepository<DomainObject>>() where dos.Id == id select dos 

Or...

from dos in ServiceLocator.Current.GetInstance<IRepository<DomainObject>>().Query where dos.Id == id select dos 

I kinda like the first one, but it's problematic to mock. How have other people implemented LINQable, mockable repositories?

Answer 1

Depends on if you want a Has-A or an Is-A relationship.

The first one is an Is-A relationship. The IRepository interface is a IQueryable interface. The second is a has-a. The IRepository has an IQueryable interface. In the process of writing this, I actually like the second better then the first, simply because when use your second IRepository, I can give the Query() method ANYTHING that returns IQueryable. To me, that is more flexible then the first implementation.