I've run into a bit of a problem.

The project I'm working on needs to store very large hierarchical tree data. Often we'll need to retrieve an entire tree from our database. The way the program is set up uses the Adjacency List method for store trees (Records have parent columns to store their relationships). This seems to be the way that it's done it Hibernate, I haven't found an example of a parent-child relationship in any other way so far.

When attempting to retrieve an entire tree of several thousand entities, I've noticed that the system needs to make several thousand SQL queries as each record needs a query to check for children. Currently on our dataset, that can take about 20-30 minutes to retrieve a single tree. It's not really a fault of Hibernate, it would be just as slow in JDBC, but more of a database design issue I think.

I'd like to modify the database to use a Modified Preorder Tree Traversal (http://www.sitepoint.com/print/hierarchical-data-database) to store and retrieve the data, as this would make retrieving a tree or any subtree performable with a single SQL query. Updates, Inserts, and Deletes would be a bit slower, but those are done gradually over time and I think not as much of an issue.

Does anyone know of a way to implement a Modified Preorder Tree Traversal in Hibernate? Am I looking at this incorrectly or perhaps using what comes with Hibernate in an inefficient manner? I've been scouring the 'net, but I haven't had much luck on this front. Any help would be greatly appreciated.

http://fisheye.jboss.com/browse/~raw,r= ... ckage.html

http://fisheye.jboss.com/browse/JBoss/j ... /nestedset

Thanks for the link to the nestedset package(s). I am trying to implement the overlay strategy outlined there, but the NestedSetDelegates for my entities do not appear to be doing anything. It appears that the Listener for inserts is not hearing about insertions.

Here's my question: how do I correctly configure my hibernate.config.xml to set the post insert listener to NestedSetPostInsertEventListener? I tried:


<property name="hibernate.ejb.event.post-insert">org.jboss.seam.wiki.core.nestedset.listener.NestedSetPostInsertEventListener</property>

But Hibernate references don't list any such property, or any similar property, so is it simply not possible to configure hibernate.config.xml as desired?

Thanks,

Josh Britton

Never mind. I now now about the event tag! But I am still wondering if it is even possible to use the nestedset classes outside an ejb environment?