I'm posting this to get some insight on how I can approach this - to have a nested tree-type structure for our objects (in our case, a Topic) which we have set up a bit differently than most examples I am able to find on this site.

I've looked up the reference guide for the parent/child relationship in a single table in the hibernate reference documentation, and most examples in there assume that the table containing the domain object will also have a PARENT_ID column, but we are attempting to keep the tree structure information, in this case, PARENT_ID separate from the actual topic table itself.

So we have a TOPIC table and a TOPIC_TREE table, and two corresponding classes, the Topic class and TopicTree class.

TOPIC
=====
TOPIC_ID

TOPIC_TREE
=========
TOPIC_TREE_ID
TOPIC_ID
PARENT_ID

In the TopicTree class (mapping given below), we have three things of interest, the parent (which can be null), the node (basically the Topic itself), and children (all Topics that have parent_id = this topic). The mapping works fine in retrieving the parent and node, but for the children set, it is retrieving the same object as the node itself. I.e. If I fetch a TopicTree item with node: Topic #3, it will also set Topic #3 in the children, instead of the children. I have tried different adjustments to the mappings, like using parent_id, or the TOPIC's topic_id with little luck.

So I am asking if this kind of mapping is possible. We are prepared to move the PARENT_ID into the TOPIC table to make this work, but wanted to ask this to the forums as a last-ditch attempt.

Thanks in advance.


Hibernate version:
2.1.6

Mapping documents:

<hibernate-mapping>
<class
name="com.foo.domain.domain.resource.TopicTree"
table="foo_topic_tree"
dynamic-update="false"
dynamic-insert="false"
>

<id
name="id"
column="topic_tree_id"
type="long"
>
<generator class="native">
<param name="sequence">foo_topic_tree_id_seq</param>
</generator>
</id>

<many-to-one
name="node"
class="com.foo.domain.domain.resource.BasicTopic"
cascade="none"
outer-join="auto"
update="true"
insert="true"
column="topic_id"
/>

<many-to-one
name="parent"
class="com.foo.domain.domain.resource.BasicTopic"
cascade="none"
outer-join="auto"
update="true"
insert="true"
column="parent_id"
/>

<set
name="children"
table="foo_topic_tree"
lazy="false"
inverse="true"
cascade="none"
sort="unsorted"
>

<key
column="topic_id"
/>

<one-to-many
class="com.foo.domain.domain.resource.BasicTopic"
/>
</set>

<property
name="displayIndex"
type="int"
update="true"
insert="true"
column="display_index"
/>

<property
name="name"
type="java.lang.String"
update="true"
insert="true"
column="name"
/>

</class>

</hibernate-mapping>


Name and version of the database you are using:
Oracle 9i