OneToOne shared PK isn't setting key in related table during insertion

[David Harkness]

I have two tables that use the same primary key generated for the "master" table in a one-to-one relationship, and I'm using JPA annotations with Hibernate 3.5.6.

class Master {
  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  private Integer id;

  @OneToOne
  @PrimaryKeyJoinColumn(name = "id")
  private Slave slave;
}

class Slave {
  @Id
  @Column(name = "master_id")
  private int masterId;    // <-- note int instead of Integer
}

When I create a new master and slave and save them together by saving the master, a 0 value is inserted into slave.master_id instead of the generated value from master.id. The problem is that it's not copying the generated ID from the Master instance to its Slave instance. If I change Slave's masterId type to Integer I get an exception instead:

org.hibernate.id.IdentifierGenerationException: 
    ids for this class must be manually assigned before calling save(): com.foo.Slave

I'm using Spring and Hibernate which I last used a few years ago so I'm basically starting over. I copied this from the example:

<property name="eventListeners">
    <map>
        <entry key="merge">
            <bean class="org.springframework.orm.hibernate3.support.IdTransferringMergeEventListener"/>
        </entry>
    </map>
</property>

and the code that saves the objects is quite basic:

public Master storeMaster(Master master) {
    return (Master) getSession().merge(master);
}

Specifying a cascadeType (ALL) has no effect. Am I missing a step? While my model does allow a Master to be saved without a Slave, I'd rather not save the Master, attach the Slave, copy the generated ID over, and save again. It just doesn't feel right.

[David Harkness]

Still no luck, but after a lot more research I've switched to a bi-directional relationship.

@Entity
@Table(name = "slave")
@GenericGenerator(name = "master_pk", strategy = "foreign", parameters = {
    @Parameter(name = "property", value = "master")
})
public class Slave implements Serializable
{
    @Id
    @GeneratedValue(generator = "master_pk")
    @Column(name = "master_id")
    private Integer masterId;

    @OneToOne
    @PrimaryKeyJoinColumn
    private Master master;
    ...
}

Master hasn't changed, and I get a new exception:

org.hibernate.id.IdentifierGenerationException: 
    attempted to assign id from null one-to-one property: master

However, in my DAO I dump out the references between the master and slave; both are valid, non-null objects. That means that either the exception is completely erroneous or Hibernate/Spring is setting the slave's master reference to null after persisting the master but before persisting the slave. That makes no sense.