JPA @ManyToOne, with additional condition

Question

I have the following entity:

@Entity
public class User {
    @ManyToOne
    @JoinColumn(name = "group_code", referencedColumnName = "code")
    private Group group;

    public User () {
    }

    // ...
}

Is it possible somehow to specify an additional condition for the above join relation? Group is hierarchical and User should always refer to the parent group, so the additional condition would be parent_group == NULL. Note that code itself is not unique.

Here is the group:

@Entity
public class Group {
    // ...

    @ManyToOne
    @JoinColumn(name = "parent_package_code")
    private Group parent;

    public Group () {
    }

    // ...
}

Answer 1

Please try to to add Hibernate's @Filter annotation. I am not aware of the whole schema, but it could be:

@ManyToOne
@JoinColumn(name = "group_code", referencedColumnName = "code")
@Filter(name="parentGroup",condition="parent_group IS NULL") 
private Group group;

In case of EclipseLink the solution could be to have separate ParentGroup entity. Then you can mark it with @AdditionalCriteria annotation and setup the mapping with User and simple Group.

Answer 2

You need to use a DescriptorCustomizer and add an Expression to the mapping in code,

http://wiki.eclipse.org/EclipseLink/Examples/JPA/MappingSelectionCriteria