具有层次结构的EF Code First属性

Question

While using Entity Framework Code First 6, I'm trying to replicate the following model:

Class A is an abstract class, implemented by A1 and A2. Additionally, class A exposes a navigation property, navigationPropertyB, to class B which is an abstract class implemented by B1 and B2.

Class A objects can have one class B object and Bs can participate multiple times in class A instances.

Currently for A I'm using Table per Hierarchy and for B Table per Concrete Type .

Class A hierarchy is mapped correctly and the following mapping is being used:

    modelBuilder.Entity<A>()
                .Map<A1>(m => m.Requires("AType").HasValue((int)AType.A1))
                .Map<A2>(m => m.Requires("AType").HasValue((int)AType.A2))

I understand it's a similar concept but I'm struggling to get a working mapping to model A's navigationPropertyB.

Can anyone help?

Thank you!

Answer 1

You're trying to create a one-to-many relationship between A and B , since each B can potentially have a relationship with multiple A s. A problem here is that since you're using Table per Concrete Type (TPC) inheritance for B 's hierarchy, you won't be able to create a single association between A and classes in the hierarchy of B . Here's a quote from your linked article on TPC :

...the SQL schema is not aware of the inheritance; effectively, we've mapped two unrelated tables to a more expressive class structure.... I have to emphasize that there is no relationship between the database tables, except for the fact that they share some similar columns.

In other words, with TPC, since the types do not share a table, it is possible to have duplicate key values across entities within B 's hierarchy!

So if you want to create an association between A and B you'll need to either

• Create a separate association with each concrete type in B 's hierarchy
• Change the inheritance mapping to TPH or TPT