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Asked: 2026-06-01T21:56:48+00:00

I have tree structures that are stored in a DB table. The table can

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I have tree structures that are stored in a DB table. The table can store multiple trees. I need a query that will return all nodes in a single tree. I’ve used the following sites as resources but the queries in them will load all nodes for all trees into PersistenceContext (isn’t that loading the entire table?). I don’t want to do that, I only want to load one tree. How do I achieve that??

I am using JPA 2 with Hibernate as the provider.

OpenJPA 1.2.x select tree structure using JPQL
http://www.tikalk.com/java/load-a-tree-with-jpa-and-hibernate#comment-1821

[UPDATE] Based upon a suggestion from @bennidi, I wonder if I can use something like this:

@Entity
public class Node {

    private String name;

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = "rootId")
    private Node root;

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = "parentId")
    private Node parent;

    @OneToMany(mappedBy = "parent", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @OrderBy("name")
    private List<Node> children = new LinkedList<Node>();
}

JPQL query:

select distinct n from Node n left join fetch n.children where n.rootId = ROOT_ID

I do have a question though, should I create a second table to maintain the Parent-Child relationships like in this article, or will it be fine if I just used a self-referencing table. Going with the former seems to require a bit more maintenance and probably a little more complex queries. Is it worth it? I’m not sure what problems the article is addressing.

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1 Answer

  1. Editorial Team

    I think it is not natural to store recursive structures in relational databases. Also the answer to your question would depend on the schema you choose to model your nodes and trees. If you have a self referencing node table that holds the parent child relations as foreign key there is no way to select all nodes that are children of a particular node with one query. I think you should have a table for each tree and have each node reference its tree. Then you can simply select all nodes of a particular tree and created the tree structure by analysing the nodes.

    Have a look at this post: http://www.codeproject.com/Articles/8355/Trees-in-SQL-databases

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