Hibernate version: 3rc1

Mapping documents:
<!-- parent -->
<class lazy="true" name="Parent" table="parent">
<id name="id" />
<property name="name"/>
<set name="children" lazy="true" inverse="false"
cascade="all-delete-orphan" sort="natural">
<key column="parent_id" />
<one-to-many class="Child" />
</set>
</class>

<!-- child -->
<class lazy="true" name="Child" table="child">
<id name="id" />
<property name="name"/>
<many-to-one name="parent" class="Parent"/>
<set name="children" lazy="true" inverse="false"
cascade="all-delete-orphan" sort="natural">
<key column="parent_id" />
<one-to-many class="GrandChild" />
</set>
</class>

<!-- grand child -->
<class lazy="true" name="GrandChild" table="grand_child">
<id name="id" />
<property name="name"/>
<many-to-one name="parent" class="Child" column="parent_id" />
</class>


Code between sessionFactory.openSession() and session.close():
Parent parent = new Parent("parent name", null);
Long id = (Long) session.save(parent);

//close session and open newSession

Child child = new Child("child name", null, null);
GrandChild grandChild = new GrandChild("grand child name", null);
child.addGrandChild(grandChild);
parent.addChild(child);

Parent parent1 = (Parent) newSession.get(Parent.class, id);
//cannot call hibSess.update(parent) because instance with the same id parent1 was loaded already
hibSess.merge(parent); //error!

Full stack trace of any exception that occurs:
when debugging to:
SortedSetType(SetType).instantiate(Object) line: 44
SortedSetType(CollectionType).replace(Object, Object, SessionImplementor, Object, Map) line: 383
TypeFactory.replace(Object[], Object[], Type[], SessionImplementor, Object, Map) line: 353
...

Because SortedSetType(SetType).instantiate(Object) return a new HashSet instead of TreeSet(for this case), a ClassCastException is thrown.
When running this test case with Hibernate 2.1, call method saveOrUpdateCopy(), no exception happens.

I think this is a bug of version 3.
Any sugestion?

P/S: Exception occurs only when merging child.children, not occur for parent.children because parent.children is a blank instance, but child.children is null value.


SortedSetType(CollectionType).replace(Object, Object, SessionImplementor, Object, Map)

I've just read <a href="http://forum.hibernate.org/viewtopic.php?t=932698">http://forum.hibernate.org/viewtopic.php?t=932698 </a>that a set (sorted=natural) must implement comparable.
In fact, this problem does not relate to comparable or not.
In the simplest case, a sorted map with key is Integer, the same exception will be thrown.