Hibernate: How to Join three 3 tables in one join table in Annotation?

Question

Can you please help me how to join three tables with one common join table? I have USER, APPLICATION, and ROLE tables. And I want thier IDs to be joined in a table named USE

Answer 1

The problem is that you have defined a relationship to roles and a separate relationship to applications. There's no declaration that any specific user is a join of both one role and one application.

When you try to associate with a role, the application is null and visa-versa.

Here's an example of mapping a 3-way join between classes A, B and C using JPA. Note, no entity is required for the join table.

@Entity
public class A {

    @JoinTable(name = "a_b_c",
        joinColumns = @JoinColumn(name = "a_id"),
        inverseJoinColumns = @JoinColumn(name = "c_id"))
    @MapKeyJoinColumn(name = "b_id")
    @ElementCollection
    private Map<B, C> cByB = new HashMap<>();

}

@Entity
public class B {
    ...
}

@Entity
public class C {
    ...
}