JPA: Using composite primary keys for map relations

Following an relation mapping example for Maps, I have

EMPLOYEE

ID  FIRSTNAME   LASTNAME    SALARY
1   Bob         Way         50000
2   Sarah       Smith       60000

PHONE

ID  OWNER_ID    PHONE_TYPE  AREACODE    NUMBER
1   1           home        613         792-7777
2   1           cell        613         798-6666
3   2           home        416         792-9999
4   2           fax         416         798-5555

Example of a map key column relationship annotation

@Entity
public class Employee {
  @Id
  private long id;
  ...
  @OneToMany(mappedBy="owner")
  @MapKeyColumn(name="PHONE_TYPE")
  private Map<String, Phone> phones;
  ...
}

@Entity
public class Phone {
  @Id
  private long id;
  ...
  @ManyToOne
  private Employee owner;
  ...
}

Is there any way to signal that OWNER_ID and PHONE_TYPE is the composite primary key?

Solution

There is no way to signal a composite primary key, because the PHONE_TYPE is part of the Map in the Employee class and OWNER_id is part of the Phone class. Beside that, that is also not your primary key: the primary key is the id property (as you have it). What you actually need is to specify a unique key over those two columns. In order to do that, one solution would be to give up the Map in the Employee class and to move the phoneType in the Phone class, where you can then add the UniqueConstraint.

PS: Of course, if you can/want you can simply the constraint on the DB-level, without any changes on the level of the Java code.