Our system has a fairly deep (5 class) and wide (total of 8 classes) hierarchy that we are trying to map to our database. Our model (at least this part) looks something like this:

(* classes are abstract)

Our current data model is TPS, which maps to 8 tables (obviously). Unfortunately, queries against this model (especially classes F and G) are very unperformant, because of the number of joins required.

We have tried several ways of mapping this structure, all of which lead to their own problems. A full TPH gives us a giant (30 column) table with scores of unrelated data. Trying to use <join> to break out a few classes allows us to get class B out of the giant subclass table, but little else.

Hibernate does not support what we would like to do, which is mix TPS and TPH within a single hierarchy, preferably by combining classes F and G into a single table per hierarchy (possibly with H) while keeping the classes above them split out.

Any advice would be much appreciated. I don't suppose there's any chance of Hibernate expanding its support of mixing TPH and TPS anytime soon?

Actually you can mix table per class hierarchy and table per subclass using a slightly modified form with a nested join element. Look in section 9.1.4 of the docs. We completely stayed away from table per subclass because of the performance hit and our domain model is quite complex. We went with TPH and TPC and have been quite pleased with the results. Sure, some of the tables are wide but who cares when hibernate takes care of transforming the records into objects.

Grant

I wanted to point people to the issue I filed on this topic, HHH-1939.

Any help, suggestions or advice would be appreciated. Thanks to Steve for his initial pointer.