Question

I’ve got 2 entities in JPA: Entry and Comment. Entry contains two collections of Comment objects.

@Entity
public class Entry {
    ...

    @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @IndexColumn(base = 1, name = "dnr")
    private List<Comment> descriptionComments = new ArrayList<Comment>();

    @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @IndexColumn(base = 1, name = "pmnr")
    private List<Comment> postMortemComments = new ArrayList<Comment>();

    ...
}

To store such objects, JPA+Hibernate creates “Entry” table, “Comment” table and SINGLE “Entry_Comment”:

create table Entry_Comment (Entry_id integer not null, postMortemComments_id integer not null, pmnr integer not null, descriptionComments_id integer not null, dnr integer not null, primary key (Entry_id, dnr), unique (descriptionComments_id), unique (postMortemComments_id))

Storing of objects fail as descriptionComments_id and postMortemComments_id cannot be “not null” at the same time.

How do I store object containing two collections of the same type using JPA+Hibernate?

Answer 1

This is one of the many Hibernate bugs (HHH-3410 to be precise).

I’ve managed to fix it by adding @JoinTable annotations to @OneToMany relationships, each having its own table name.

In your case it would look like this:

@OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
@JoinTable(name="entity_descriptioncomments")
@IndexColumn(base = 1, name = "dnr")
private List<Comment> descriptionComments = new ArrayList<Comment>();

@OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
@JoinTable(name="entity_postmortemcomments")
@IndexColumn(base = 1, name = "pmnr")
private List<Comment> postMortemComments = new ArrayList<Comment>();

Note: you must add @IndexColumn annotation as well (because of the other Hibernate issue with multiple EAGER bags: HHH-1718/EJB-346).