Question

Suppose I have 2 JPA entities:

@Entity
public class OwnerEntity {

    private List<OwnedEntity> subEntities

    // ...
}

@Entity
public class OwnedEntity {

    private String quasiUniqueSid;

    private OwnerEntity ownerEntity

    // ...
}

As you can see they have a many to one relationship: an OwnerEntity can have many OwnedEntitys.

What I want to achieve is to assign each OwnedEntity a unique sid based on its owner. So I can have for example 2 owned entities with the same quasiUniqueSid but they cannot have the same owner. Do Hibernate has some built-in functionality for this kind of problem? I can remember other ORMs (not Java related) which could do this thus my question. I’m using the latest Hibernate version (4.1.8)

Answer 1

It seems you need a composite key, like this:

@Entity
@Table(uniqueConstraints=@UniqueConstraint(columnNames={"quasiUniqueSid","ownerEntity_id"}), name="myUniqueConstraint")
public class OwnedEntity {
    ...
    String quasiUniqueSid;
    @ManyToOne
    OwnerEntity ownerEntity;
    ...
}

A full documentation you can find here.

If you wanna explicitly define the column name for ownerEntity, you can use:

@JoinColumn(name="ownerEntity_id")