Use of @EmbeddedId and @MapsId causes NULL inserted (NOT NULL constraint violation)

Question

With using following code

@Embeddable
public class EmployeeId implements Serializable {
    @Column(name = "company_id")
    private Long companyId;

    @Column(name = "employee_id")
    private Long employeeNumber;
}

@Entity
public class Employee {
    @EmbeddedId
    private EmployeeId id;

    private String name;

    @MapsId("name=companyId")
    @ManyToOne
    @JoinColumn(name = "company_id")
    private Company company;
}

When trying to persist or merge the Employee Entity, we can see that a NULL as attempted to be inserted into the company_id field.

How can I avoid a NULL to be inserted?

Answer 1

Even with the wiring, when creating a new object (not fetched from the persistence context), the company field will remain null.

When Creating a new Employee entity, you will need to assure that you also initialize the company attribute:

@Entity
public class Employee {
    @EmbeddedId
    private EmployeeId id;

    private String name;

    @MapsId("name=companyId")
    @ManyToOne
    @JoinColumn(name = "company_id")
    private Company company;

    public Employee() {}

    public Employee(int id,String name,Company company) {
      this.name = name;
      this.id = new EmployeeId(id,company.id);
      this.company = company;
    }
}

The Company entity you might acquire from the persistence context using a find. You also can create it from scratch using it's constructor.