Recursive - Directed Acyclic graph (tree/parent-child ) entity management using 'modified preorder tree traversal algorithm' ----------------------------------------------------------------------------------------------------------------------------- Key: HHH-1395 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-1395 Project: Hibernate3 Issue Type: New Feature Components: core, query-hql Environment: Hibernate 3.1 plus Annotations extending EJB3 implementation Reporter: James Salt Attachments: nestedset.tar.gz Original Estimate: 3 weeks Remaining Estimate: 3 weeks An enhancement to allow entities to exist in a managed tree (DAG) structure, via the use of property annotations and entity annotations. With an extension to the HQL language to mimic the Oracle recusive query clause. This would be classically be useful for Bill of Material uses, or any tree like entity structure. I have implemented a homebrew approach using the 'adjacency list method' , and a post persist call back method to set the node path. Although I think a more full blown optimised algorithm would be the 'modified preorder tree traversal algorithm'. In the annotations world this could be implemented using an annotation like @Hierarchical to the entity, with a @Parent (mask for @ManyToOne) annotation on the parent field/parameter and @Children (mask for @OneToMany) annotation on the list of children entities. Then a postupdate method could be implemented for the entity type, that recalculates the tree meta data -i.e. parent, left and right. I believe this would be a valuable extension (useful for many common data models) to the hibernate core product that could be exposed through annotations as I have discussed and the hbm.xml. The users of such a system would be aware of the performance implications on insert/update/delete, but gain a massive performance gain on querying a tree data model.