JPA Unique constraint on nested entities

Question

Having three entities, that are nested, say A{b} , B{c} , C{id} Can I use JPA's unique constraint annotation to access C's id on A?

My scenario: I have some other field "z" on A, and I want to impose that "z" and c's "id" are uniquely associated

Answer 1

Queries

You can join those tables without any configuration changes using the 'old' style join. It enables you to link entities by columns which are not linked directly:

select a 
From A a, C c
Where a.z = c.id

Mapping

If you want to change the configuration try this:

public class C{

    @ManyToOne
    @JoinColumn(name = "id", referencedColumnName = "z")
    private A a;

}

public class A{

    @OneToMany(mappedBy = "a"
    @JoinColumn(name = "z", referencedColumnName = "id")
    private List<C> cCollection;

}