问题
I am trying to use the new asp.net identity provider with my abstraction layer of my models domain, wich have a implementation of Entity Framework, so I would like to use the out of box version of identity with entity framework in my data access layer.
How can I convert an
UserStore<IdentityUser>
to its base interface
IUserStore<IUser>
Once UserStore is an implementation of IUserStore, I can get the cast by this:
UserStore<IdentityUser> as IUserStore<IdentityUser>
But I want to avoid the IdentityUser from EntityFramework references and dependences, to keep my domain layer loosely coupled. So, IdentityUser also are an implementation of IUser I can cast it:
IdentityUser as IUser
Both cases works, then I would like to do some like this (wich in fact doesnt works directly):
UserStore<IdentityUser> as IUserStore<IUser>
So, how can I achieve this?
If we look at this diagram http://i3.asp.net/media/4459023/1.png, we will see what I would like to achieve. Referencing just the Microsoft.AspNet.Identity.Core in my domain layer, but using Microsoft.AspNet.Identity.EntityFramework implementation at DataAccess layer by returning the core interfaces for the domain layer.
回答1:
The cast doesn't work because UserStore<UserIdentity> is not the same as UserStore<IUser> (even if IdentityUser implements IUser).
If you need UserStore<IUser> then I suggest you implement it in that way and cast to the concrete type internally, you can ensure that the concrete type is IdentityUser with a constraint e.g.
public class UserStore<T> : IUserStore<T> where T: IUser
{
}
You would also need to make your interface covariant i.e.
public interface IUserStore<out T> where T : IUser
{
}
This should allow you to do the following (assuming IdentityUser supports IUser)
IUserStore<IUser> userStore = new UserStore<IdentityUser>();
来源：https://stackoverflow.com/questions/19929050/how-to-cast-userstoreidentityuser-to-its-base-class-iuserstoreiuser