Hibernate version: 3.0.5

So, I have a three tiered inheritance hierarchy:

I start with base class A which has its own db table. Class B subclasses A, has its own db table, and is mapped using <joined-subclass>. Classes C and D subclass B, but have no additional fields and therefore do not need their own additional db tables. It makes sense that the inheritance relationship between class B and its subclasses C and D should be mapped with a table-per-hierarchy style, which would require a discriminator column in class B.

This is where my problem comes in. Remember that class B is a <joined-subclass> because it extends class A. The mapping DTD does not allow <discriminator> inside of a <joined-subclass>, and my project won't deploy when I put one in. This prevents me from mapping classes C and D in a table-per-hierarchy with class B.

Is forbidding <discriminator> in <joined-subclass> simply an oversight or is there a technical reason for this? Is there a solution to this problem that I am overlooking? Please note that I know I can make separate tables for classes C and D that contain only ids in order to make C and D joined-subclasses as well, but this fills my db with dummy tables and I'd naturally like to avoid that.

Thanks much for you consideration in this issue!

Hi,

we had the same problem.
Hibernate does not support the mixing of inheritance strategies.
There are two solutions to this:

1. Write DTO classes for B,C and D. These can be mapped by discriminator
hierarchy. And map class A to its table directly. You certainly have more to do manually when loading and saving.

2. write you own persister class. You can look at JoinedSubclassEntityPersister for a starter. This is certainly difficult.

Hope this helps.