List<T> to implement IQueryable<T>

Question

I'm trying to create a mock for my IRepository interface:

public interface IRepository<T> : ICollection<T>, IQueryable<T> { } 

With this implementation:

public class RepositoryFake<T> : List<T>, IRepository<T> {     public Expression Expression     {         get         {             return this.AsQueryable().Expression;         }     }      public Type ElementType     {         get         {             return this.AsQueryable().ElementType;         }     }      public IQueryProvider Provider     {         get         {             return this.AsQueryable().Provider;         }     } } 

But when I use it, I'm getting StackOverflow exception. How to implement this interface correctly to be able to use just a List as a repository?

Usage is very simple

[Test] public void Test() {     RepositoryFake<User> users = new RepositoryFake<User>();     users.Add(new User());      List<User> list = (from user in users                   where user.Id == "5"                  select user).ToList();      Assert.That(list, Is.Empty); } 

Here is screenshot of exception:

Answer 1

The reason for your problem is that if you perform AsQueryable it checks if the object already implements IQueryable and if yes returns it.

Use new EnumerableQuery<T>(this) instead of AsQueryable which doesn't perform this check.

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Workaround for .net 3.5:

return ((IEnumerable<T>)this).Select(x=>x).AsQueryable() 

First casts to IEnumerable<T> so the chosen Select method will be Enumerable.Select not Queryable.Select. The identity select will then return a new object that does not implement IQueryable<T>, so the check if it's implemented in AsQueryable fails.

Answer 2

Try using base.AsQueryable() instead of this.AsQueryable().