Hibernate: null index column for collection in one-to-many relation

Question

I'm trying to map a one-to-many / many-to-one relationship in Hibernate with a List of child entities. Doing the same with a Set on other relations works find, but I need to have a List with order of child-entities.

What I've done so far is this:

@Entity
@Table(name="event")
public class Event {
    @OneToMany(mappedBy="event", fetch=FetchType.EAGER) 
    private List<Message> messages; //Message entitiy is the child
//getters+setters+and some other stuff like id
}

And here's the ManyToOne side:

@Entity
@Table(name="message")
public class Message{
    @ManyToOne
    @JoinColumn(name="eventid")
    private Event event;
//getters+setters+and some other stuff like id
}

On this I can insert a Message, it will be added to the database (postgres). But problem is on getting the messages as a List: I get 2 results of the same Message when only one was added and is visible on the database!

Of course, I've done some research and found that an index is needed on a List. But nothing I've tried, worked out. All I got is an exception of: "null index column for collection...". None of the solutions I've found on here and via google seemed to work and there are so many "solutions" that I don't really know which of those are even supposed to work!

Does anyone have an idea on how to realize this relation? I'd be greatfull for any advice!

Thank you!

Answer 1

I have the same problem with an old version of hibernate (3.5.6) and find one good non-invasive workaround: try to change your List<Message> to Set<Message> Object and use HashSet instead of ArrayList.

Good luck!