nested set
http://www.developer.com/db/article.php/3517366

materialized path
http://philihp.blogspot.com/2008/05/usi ... trees.html

So i've been reading about these two patterns for optimized tree persistence in a relational DB and i think i'm starting to understand how they work but i have a question...

If i were to implement one of them it would give me a quick way of selecting all of the sub nodes of any location in the hierarchy. But! How do i convince hibernate to organize the instantiated objects as a tree.

What happens is i get a flat list of all of the nodes and if you touch one of the children it queries the DB to load them. Just for the heck of it i tried to manually stuff one of the children into it's parent programatically but that didnt resolve the issue. (it still queried the DB but now i had a duplicate instance of the child object)

I just had an epiphany about this. The 'problem' here is that hibernate tries to read the children because there is a one-to-many mapping to teach hibernate how the hierarchy is structured. If you use a strategy like Materialized Path or Nested Set you still in cure a DB query to find the children because hibernate doesn't know that you found them all by other means. I think that the solution here is to use hibernate the read all of the records for nodes below your chosen node and then use java to associate the instantiated objects. But for this to work without additional db polling i'd also need to remove hibernate collection annotation defining the one-to-many join.

I think that this will work.

I´m very interested in this topic currently.

I came across the same idea of manually handling the relation between objects in Java.

Did you try this or did you come to another solution to the problem?