In our legacy schema, we have a two level master slave association with composite primary key layered as follows:

Dept: id (generated by sequence)
Div: (dept_id, div_id): div_id is a list index
Unit: (dept_id, div_id, unit_id) unit_id is again a list index

My first impulse is to model this association as a nested collection of components, but since the composite-element does not allow another collection, I try to model them as collection of entities with composite key. Here are my mappings:

Dept:

<hibernate-mapping>
<class name="Department" table="DEPT">
<id name="id" column="ID">
<generator class="sequence">
<param name="sequence">DEPT_SEQ</param>
</generator>
</id>
<property name="name" column="NAME"/>
<list name="divisions" table="DIVISION" cascade="save-update">
<key column="DEPT_ID" />
<list-index column="DIV_ID"/>
<one-to-many class="Division" />
</list>
</class>
</hibernate-mapping>

Div:

<hibernate-mapping>
<class name="Division" table="DIVISION">
<composite-id >
<key-property name="deptId" column="DEPT_ID"/>
<key-property name="divisionId" column="DIV_ID"/>
</composite-id>
<property name="name" column="NAME"/>
</class>
</hibernate-mapping>

(Unit is not included, since just Dept-Div already fails)

This follows the example in section 8.4 of the reference manual, except the relation is unidirectional. The cascade is save-update. Hibernate does not populate composite key and so I populate divId myself. I cannot populate deptId in Division, because the value is generated by the sequence and is not known beforehand.

When I try to save the department object, I got this exception:

Caused by: java.sql.BatchUpdateException: ORA-01400: cannot insert NULL into ("REALESTATEBOARD"."DIVISION"."DEPT_ID")

at oracle.jdbc.driver.DatabaseError.throwBatchUpdateException(DatabaseError.java:498)
at oracle.jdbc.driver.OraclePreparedStatement.executeBatch(OraclePreparedStatement.java:12410)

The SQL parameter spit out with debug turned on is:

Hibernate:
insert
into
DIVISION
(NAME, DEPT_ID, DIV_ID)
values
(?, ?, ?)
16:27:23,065 DEBUG StringType:80 - binding 'development' to parameter: 1
16:27:23,066 DEBUG LongType:73 - binding null to parameter: 2
16:27:23,067 DEBUG LongType:80 - binding '2' to parameter: 3

This shows that with cascade save-update, dept_id is not populated by hibernate. Do I have to switch to use cascade="none" and then populate the deptId field mannually?

I found the solution in this thread:

http://forum.hibernate.org/viewtopic.ph ... ey+cascade

The solution is handled by the key-many-to-one tag. This is my final mapping(for one level):

<class name="Department" table="DEPT">
<id name="id" column="ID">
<generator class="sequence">
<param name="sequence">DEPT_SEQ</param>
</generator>
</id>
<property name="name" column="NAME"/>
<set name="divisions" table="DIVISION" cascade="all,delete-orphan" inverse="true">
<key column="DEPT_ID" />
<one-to-many class="Division"/>
</set>
</class>

<class name="Division" table="DIVISION">
<composite-id name="id" class="DivisionKey">
<key-many-to-one name="department" column="DEPT_ID" class="Department"/>
<key-property name="divisionId" column="DIV_ID"/>
</composite-id>
<property name="name" column="NAME"/>
</class>

DivisionKey contains a Department field and a divisionId field.