I have an object which contains a collection that contains a set and I get the "Illegal attempt to associate a collection with two open sessions" error when I try to remove the last member of the main collection.

So TABLE A contains a collection of 0 or more of TABLE B. TABLE B may or may not have a set of TABLE C.

The mapping for TABLE B is :

<class name="Company" table="TABLE_B">
..
..
..
<set name="divisions" table="TABLE_B_C">
<key column="TABLE_B_ID>
<many-to-many column="DIVISION_ID" class="Division"/>
</set>
</class>

TABLE_B_C is the mapping table that has a composite primary key of TABLE_B|TABLE_C. These are foreign keys to there respective tables.

Data in TABLE_B can exist without an association to TABLE_C and vice versa.

The error does not occur when Company actually has divisions mapped to it.

Can I do this? Is there another way to map this?

I am using hibernate 2.