How to create child object of existing super object, using JOINED inheritance strategy and Hibernate

Question

what is the appropriate way how create child object of persisted super object with Hibernate?

Consider following example: In database is persisted User with ID 1, firstName Kevin and laseName Smith. By the time is database model extended of new Entity Auditor which is child class of User. For inheritance is used strategy JOINED, so database model now has tow tables: user and auditor. These tables are jointed using user_id FK.

I would like create of Kevin Smith object type Auditor and persist. Problem is that operations are transactional and Hibernate throws NonUniqueObjectException. Exists any way how to safely cast persisted object do child object? I tried to evict given User object, but still the same.

User entity

@Entity
@Table(name = "user")
@Inheritance(strategy = InheritanceType.JOINED)
public class User{

    private Long id;
    private String firstName;
    private String lastName;

    // getters and setters
}

Auditor entity

@Entity
@Table(name = "auditor")
public class Auditor extends User {
  // some properties
}

Logic

public void createAuditorOfUser(final long userId) {
  final User user = userService.getUserById(userId);
  // ...
  final Auditor auditor = new Auditor();
  auditor.setId(user.getId());
  auditor.setFirstName(user.getFirstName());
  auditor.setLastName(user.getLastName());
  userService.evict(user);
  // will throw  NonUniqueObjectException
  auditorService.update(auditor);
  // ...
}

I hope the problem is clear, if not I'll try improve description.

Answer 1

I think Hibernate intentionally restrict such behaviour. Of course you can do it with native SQL workaround (as you already did).

In Java also we can't cast an object of super class to a sub-class then fill new fields of same object. Instead, create a new instance of sub-class then copy fields.

Seems like one-to-one relation mapping fits better for the functionality you required.