.net - 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.