CODEWITHSUNDEEP
wordpresshibernatejpa
Robert van der Spek
Robert van der Spek

Reputation: 1197

How to map OneToMany within a table?

o-o!

I am trying to map the wp_posts table from WordPress database. I have left out information to simplify my question:

This is the entity:

@Entity
@Table(name = "wp_posts")
@Getter
@Setter
public class WPPosts {

    @Id
    @Column(name = "ID")
    private long id;

    @Column(name = "post_parent")
    private long postParent;

    @OneToMany(targetEntity = WPPosts.class, mappedBy = "postParent")
    List<WPPosts> childPosts;
}

An example for the table could be (again: simplified!):

id --- post_parent
1 ---- null
2 ---- 1
3 ---- 1
4 ---- null

So entity with id 1 should get a list childPosts of size 2 (containing post 2 and 3).

Unfortunately this does not work. I do not get any exception, but the list stays empty.

Upvotes: 0

Views: 41

Answers (1)

crizzis
crizzis

Reputation: 10716

mappedBy is supposed to be referring to an entity, not an id. You need a @ManyToOne WPPosts postParent field for your mapping to work.

Note that with such a mapping, WPPosts.postParent is the owning side of the relationship, meaning that only changes to WPPosts.postParent will be honored by JPA; changes to WPPosts.childPosts will be ignored.

As far as accessing the list goes, you'll want to ensure to either only access the list within a transaction context, or declare the @OneToMany as fetch=FetchType.EAGER. Otherwise, you'll get lazy initialization exceptions.

Upvotes: 1

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