Composite primary key and ManyToOne hibernate-CodePudding

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.

CodePudding user response：

Question really is, which entity should be the owner of the relationship? would you like to map bidirectional or single way?

Here is the bidirectional example

@OneToMany(
      fetch = FetchType.EAGER,
      mappedBy = "department",
      orphanRemoval = true,
      cascade = CascadeType.ALL)
private List<Worker> workers;


@JoinColumn(name = "department_id", nullable = false)
@ManyToOne(targetEntity = Department.class, fetch = FetchType.LAZY)
private Department department;

fetch types are optional and depend on the use case

CodePudding user response：

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")
    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.