JPA query for getting the whole tree

Question

Hello,

I have a class which models all categories and they can be ordered hierarchically.

@Entity
@Table(name="categories")
public class Category {
    @Id
    @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="sequence")
    @SequenceGenerator(name="sequence", sequenceName="categories_pk_seq", allocationSize=1)
    @Column(name="id")
    private Long id;

    @Column
    private String name;

    @OneToOne
    @JoinColumn(name="idfather")
    private Category father;

}

I need to get all categories ordered hierarchically (I mean every father followed by its children and fathers ordered alphabetically on each level) as they could be made for example with PRIOR in oracle. Is it possible to do this with a JPA Query (not a SQL one)?

Thanks.

Answer 1

The short answer is; no there isn't a standard way to do this.

You have to use native sql.

You may be able to extend the Oracle Hibernate Dialect and add some user function/extension to get hibernate to generate PRIOR or CONNECT BY clauses, but this will prevent your app from being strict JPA and database independent.