Entity Framework Inheritance

Question

I am interested in a rather peculiar inheritance strategy and how it could be implemented in Entity Framework 4.0. I've done some reading around, but I'm not sure that any of the three standard solutions are applicable (table-per-type, table-per-hierarchy, table-per-concrete-type).

I shall generalise my problem into an easier one. Let's say I have an abstract base class entity B, and two derived entities D1 and D2.

Now, D1 and D2 are mapped onto separate defining queries - even though they share properties in common due to their shared base class B, these properties are not pulled from the same place in the storage.

All is fine so far, but I really need to be able to expose an ObjectSet<B>, i.e. a collection unioning D1 and D2 items.

Is this possible?

Thanks in advance for any help.

EDIT: Here's some more detail as requested.

Entity POCOs

public abstract class B {
    public int ID { get; set; }
    public DateTime SomeDate { get; set; }
}
public sealed class D1 : B {
    public string SomeInfo { get; set; } 
}
public sealed class D2 : B {
    public decimal SomeNumber { get; set; }
}

I can't get the XML to format properly, but basically D1 is mapped onto a defining query and D2 is also. I cannot map B onto anything, as it varies depending on the subtype.

How does TPC not handle that? You description lacks detail. Better work it out with a few small table definitions. — Henk Holterman
I've added the entities. There are no tables; it is a readonly mapping - the entities map to queries, and there is nothing shared in common between D1 and D2 (although the ID is guaranteed to be unique). I cannot see how EntityFramework will provide me with a ObjectSet<B> — Stephen Drew
Here's the problem: when I try to get an ObjectSet<D1> I get an error from MSL saying I have not mapped the entityset for B. However,there is no direct mapping for B, just for D1 and D2. — Stephen Drew

W3t Tr3y W3t Tr3y · Accepted Answer · 2011-03-02T20:13:32

This would be a bit of a cheat, but could you combine the sets in the database and then pull that into the entity framework? You would probably need to create an entity which had all the properties and if the property did not exist in B (i.e. in D1 or D2 only) then it would have to be nullable.

Entity Framework Inheritance

1 Answers