My subject is to implement a tree structure in hibernate. The tree represents a project structure with many folders and files. It can be expected that the content of this tree will grow over the time.

My question is: how can this be done in a performant manner. I currently have a simple table representing the item with a self-reference on another item. To show the structure in a tree control, i have to ask about the possible children of a leaf (representing the "+" at the beginning).

Are there any howtos or documentation or can anyone help me with this issue?

Lazy loading is a problem, as all items will be converted into DTOs (mapping within a 3-tier-architecture). So any other solutions welcome!

Here is an article about how to store trees in database: http://www.weckert.org/nst/index.html There are 2 solutions: "Adjacency Lists" and "Nested Sets". Read the advantages and disadvantages of every one. Note that in case of "Adjacency Lists" solution there are databases (like Oracle and MS SQL) that support recursive queries; these are proprietary solutions so I do not think you can translate them to HQL. For one of my projects I used "Nested Sets" and I did not encountered any difficulties.