I have a many-to-many which is self referencing. I need one end of the relationship to keep a list of children. This is working fine, except the list-index is not being updated when a new Category is added to the list of children. Any ideas? The relevant parts of the mapping are:

<class name="software.executiveutilities.model.Category" table="CATEGORIES" lazy="false">
<id name="id" column="ID">
<generator class="increment" />
</id>


<list name="children" table="CATEGORY_CHILDREN" lazy="false" inverse="false">
<key column="PARENT_CATEGORY_ID" not-null="true" />
<list-index column="CHILD_ORDER" base="0" />
<many-to-many column="CHILD_CATEGORY_ID" class="software.executiveutilities.model.Category" />
</list>

<join table="CATEGORY_CHILDREN" optional="true">
<key column="CHILD_CATEGORY_ID" unique="true" />
<many-to-one name="parent" column="PARENT_CATEGORY_ID" not-null="true" class="software.executiveutilities.model.Category" />
</join>

</class>

I still can't seem to get the list-index to be updated. I have changed my approach to try and implement something like this http://www.hibernate.org/193.html even though from what I have read I should be able to do indexed collections in a bidirectional association with Hibernate 3. Using this Hibernate 2 approach my new mapping like this:

<list name="children" table="CATEGORIES" lazy="false" inverse="false" >
<key column="PARENT_ID" />
<list-index column="CHILD_ORDER" base="0" />
<one-to-many class="software.executiveutilities.model.Category" />
</list>

<many-to-one name="parent" column="PARENT_ID" class="software.executiveutilities.model.Category" />
<property name="childOrder" column="CHILD_ORDER" type="int" update="true" insert="true"/>


Now according to the documentation, this should work :

private int getChildOrder()
{
return this.getParent().getChildren().indexOf(this);
}


private void setChildOrder(int index)
{
// not used, calculated value, see getIndex() method
}


I can understand how this would work for retrieving the childOrder from a given Category, but how does this work for setting the order? When I add a new child Category to the list, the childOrder of children is still not being updated. Do I have to do these updates to Category.childOrder manually? For example, add a new Category to the list of children, then go through each of the children and set their childOrder approriately? Surely, there is a better way? This seems WAY to difficult to maintain. Any help is MUCH appreicated.