Hibernate Mapped Superclass relationships and overriding

Question

I have an abstract MappedSuperClass, Participant, which is extended by three kinds of 'Participant'. Each one then uses its own kind of 'Project', also an abstract MappedSuperClass. However, I want the base class to know about Projects so I can write generic code to interact with Participants. How do I specify this using Hibernate annotations? and how will I override it in the ExtendedParticipant and ExtendedProject classes?

Each Participant type, and each Project type, have their own database tables with existing data and ids (not unique across tables) that I cannot change.

The following code gives me the IDE error "Many to one attribute should not be 'Mapped Superclass'".

@MappedSuperclass
public abstract class Participant implements Persistable {

    ...

    @ManyToOne
    @JoinColumn(name = "project_id")
    public Project getProject() {
        return project;
    }

    public void setProject(Project project) {
        this.project = project;
    }

    ...
}

and the Project class is much the same with the same problem:

@MappedSuperclass
public abstract class Project implements Persistable {

    ...

    @OneToMany
    public List<Participant> getParticipants() {
        return participants;
    }

    public void setProject(List<Participant> participants) {
        this.participants = participants;
    }

    ...
}

Solution

A mapped superclass is not an Entity, it can't be part of an association. So map your classes as entities and either introduce a mapped superclass "above" them or use a TABLE_PER_CLASS strategy.

See also

• EclipseLink: Query to MappedSuperclass fails
• Hibernate - Persisting polymorphic joins

Comments

[Andrew]

Thanks Pascal, that make sense. I saw another post you had commented on about this but I'm still unsure what to do about it. There must be a way to set up all the relationships using base classes?

[Devanshu Mevada]

@Andrew: Well, why are they mapped superclass? Can't you put the common properties in a class above them? Another "option" would be to map them as entities and use a TABLE_PER_CLASS strategy.

[Andrew]

The 3 ExtendedParticipant classes share many field names, so I had hoped to put all that into the base class, which is why I chose a Mapped SuperClass. I guess I could have a base class with no mappings, but then I would have to include every field in every ExtendedParticipant...