What is the best way to cast each item in a LINQ to Entities query to an interface?

Question

I have an entity object 'User' which implements 'IUser':

IQueryable<User> users = Db.User;
return users;

But what I actually want to return is:

IQueryable<IUser>

So what is the best way to convert

IQueryable<User>

to

IQueryable<IUser>

without actually running the query? Right now I am doing this but it seems like a hack:

IQueryable<IUser> users = Db.User.Select<User, IUser>(u => u);

Craig Stuntz is correct: L2E doesn't support the Cast method. If fails with: "Unable to cast the type 'MyType' to type 'MySubTypet'. LINQ to Entities only supports casting Entity Data Model primitive types.". I deleted my answer since it didn't provide any value. — bruno conde, Aug 06 '09 at 17:17
Doesn't this eager load the results? it doesn't get the whole table when for each part of the query? — Maslow, Feb 23 '12 at 22:37
Which .NET version? In .NET 4 you should be able to assign any IQueryable to a variable of type IQueryable without the need for a cast of all the entries is the list... — jessehouwing, May 04 '12 at 20:03

Craig Stuntz · Accepted Answer · 2009-08-06T17:20:02.737

5

Your "hacky" solution looks fine to me.

edited Aug 06 '09 at 17:20

answered Aug 06 '09 at 16:55

Craig Stuntz

I just tried that with the following exception: The 'TypeAs' expression with an input of type 'Bla.User' and a check of type 'Bla.IUser' is not supported. Only entity types and complex types are supported in LINQ to Entities queries. – Mike Comstock Aug 06 '09 at 17:18
Thanks for the test. I'll remove the alternative. – Craig Stuntz Aug 06 '09 at 17:19
Thanks for the speedy responses Craig! – Mike Comstock Aug 06 '09 at 17:25

1 Answers1