Composite primary key and ManyToOne hibernate - spring-boot

Question

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.

Answer 1

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.

Answer 2

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