Hibernate version: 3.2.5.ga

In our DB schema we have identifying One-To-Many relations, with slave tables containing foreign key as a part of primary key.

When we annotate slave collection with @OneToMany and delete items from collections, Hibernate issues UPDATE slave SET fk=null, which, of course, fails.

What annoation(s) we can use to make Hibernate issuing DELETE FROM instead of UPDATE SET NULL?