[FIXED] Composite primary key and ManyToOne hibernate

Issue

I'm learning Hibernate and I'm trying to make the Mapping work. My entities are as follows

Department:

@Entity
public class Department {

    @Id
    @GeneratedValue
    private Integer id;
    private String name;
    private String hqLocation;
    // getters and setters omitted for brevity 
}

WorkerId:

@Embeddable
public class WorkerId implements Serializable {

    private Integer workerId;
    private Integer deptId;
    // getters and setters omitted for brevity 
}

Worker:

@Entity
public class Worker {

    @EmbeddedId
    private WorkerId id;
    private String name;
    private Integer age;

    // How to make @ManyToOne mapping work?
    private Department department;
    // getters and setters omitted for brevity 
}

Question: How to make @ManyToOne on the field private Department department; work? Simply adding the annotation results private Department department; as null.

Solution

I think you want to use a "derived identity"; so you should make Worker.department like this:

@Entity
public class Worker {

    @EmbeddedId
    private WorkerId id;
    private String name;
    private Integer age;

    @MapsId("deptId")
    @ManyToOne      // <<<< edit
    private Department department;
    // getters and setters omitted for brevity 
}

Derived identities are discussed (with examples) in the JPA 2.2 spec in section 2.4.1.

Answered By - Brian Vosburgh
Answer Checked By - Pedro (JavaFixing Volunteer)