Hibernate Polymorphism (Extending Parent Class)

Question

Question regarding Hibernate Polymorphism and extending a parent class (which I can not modify directly). My parent class is called Contact:

@Entity 
@Table(name="contact")
@Inheritance(strategy=InheritanceType.JOINED) 
public class Contact {
  @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
  public long id;
  public String name;
} 

And the child class is called ContactLocation which associates a Location to a Contact:

@Entity 
@Table(name="contact_location") 
@Inheritance(strategy=InheritanceType.JOINED) 
public class ContactLocation extends Contact {
  @ManyToOne(targetEntity=Location.class, cascade=CascadeType.ALL)
  Location location;
}

The resulting database table structure appears to be correct:

contact: 
 id:long 
 name:varchar

contact_location: 
 contact_id:long 
 location_id:long

Here's my save method which I need to either update an existing ContactLocation, or save a new ContactLocation for an existing Contact:

public void saveContact(Object dialog) { 
  Contact contact = ui.getAttachedObject(dialog, Contact.class); 
  ContactLocation contactLocation = null; 
  if (contact instanceof ContactLocation) { 
     LOG.debug("Casting Contact to ContactLocation"); 
     contactLocation = (ContactLocation)contact; 
     //TODO Update existing ContactLocation
     //UPDATE contact_location SET location_id = 33 WHERE contact_id = 22;
  } 
  else { 
     LOG.debug("Contact NOT instanceof ContactLocation"); 
     //TODO Save new ContactLocation from existing Contact
     //INSERT INTO contact_location (contact_id, location_id) VALUES (22,33);
  }
}

How do I create a row in *contact_location* table which maps Contact to a Location using my ContactLocationDao?

Answer 1

There is no support for objects changing type after creation that I'm aware of. You'll have to create a new ContactLocation object, update possible references and then delete the original Contact, I'm afraid.