How can I cast to subclass when using LINQ and TPT EF? - entity-framework

Question

I have the following class hierarchy:
public class RealPeople { }
public class Users : RealPeople { }
public class People : RealPeople { }
In my dbContext, I defined a dbSet for RealPeople and on the OnModelCreating procedure, I specified separated tables for People and Users:
modelBuilder.Entity<Users>().ToTable("Users");
modelBuilder.Entity<People>().ToTable("People");
This creates the corresponding full hierarchy in my DB, with the 3 corresponding tables.
The problem comes when I want to retrieve the list of Users in my DB.
This:
List = (from Reg in PersistentMgr.RealPeople select (Users)Reg)
.ToList();
or this:
List = (from Reg in PersistentMgr.RealPeople select (Users)((RealPeople)Reg))
.ToList();
Throws an exception:
LINQ only being able to cast primitive model types.
So the thing is, I can't cast RealPeople to the corresponding subclass Users.
Any ideas on this one?

Answer 1

The way to get a collection of subclasses is using OfType:
var users = (from p in PersistentMgr.RealPeople select p).OfType<User>();

Answer 2

Try this instead:
var list = PersistentMgr.RealPeople.Select(reg => reg as Users).ToList();
better:
var list = PersistentMgr.RealPeople.Select(reg => (reg is Users) ? reg as Users : null).ToList();
You will get the same error if you try this:
var realperson = new RealPeople();
var user = (Users) realperson;
The reason is because the compiler doesn't know how to convert complex types into their subtypes by simple casting - so you need to use the as keyword instead. This will either return null, or the supertype casted into the subtype.
var realperson = new RealPeople();
var user = realperson as Users; // user is realperson converted into a Users object
var aString = "this is a string";
var otheruser = aString as Users; // otheruser is null, because aString was not a valid supertype for Users