Why @OneToMany does not work with inheritance in Hibernate

In my case I wanted to use the SINGLE_TABLE inheritance type, so using @MappedSuperclass wasn't an option.

What works, although not very clean, is to add the Hibernate proprietary @Where clause to the @OneToMany association to force the type in queries:

@OneToMany(mappedBy="person")
@Where(clause="DTYPE='UP'")
private List< UglyProblem > problems;

I think it's a wise decision made by the Hibernate team. They could be less arrogante and make it clear why it was implemented this way, but that's just how Emmanuel, Chris and Gavin works. :)

Let's try to understand the problem. I think your concepts are "lying". First you say that many Problems are associated to People. But, then you say that one Person have many UglyProblems (and does not relate to other Problems). Something is wrong with that design.

Imagine how it's going to be mapped to the database. You have a single table inheritance, so:

          _____________
          |__PROBLEMS__|          |__PEOPLE__|
          |id <PK>     |          |          |
          |person <FK> | -------->|          |
          |problemType |          |_________ |
          -------------- 

How is hibernate going to enforce the database to make Problem only relate to People if its problemType is equal UP? That's a very difficult problem to solve. So, if you want this kind of relation, every subclass must be in it's own table. That's what @MappedSuperclass does.

PS.: Sorry for the ugly drawing :D