I have two classes Client and Drivingdistance with a one to one association. The id of the Client is the PK and FK in DrivingDistance. My mapping annotations are as follows:

Client class:

@Table(name="FBCLIENT")
@Name("client")
@Scope(ScopeType.SESSION)
public class ClientVO implements Serializable
{
 @Id @NotNull @Column(name="CLIENTID")
 public Long getId() {
 return id;
 }
 @OneToOne(cascade = CascadeType.ALL)
 @PrimaryKeyJoinColumn()
 public DrivingDistanceVO getDrivingDistance()
 {
 return drivingDistance;
 }
...}

Driving Distance

@Entity
@Table(name="FBDRVDSTNC")
@Name("drivingDistance")
public class DrivingDistanceVO implements Serializable
{
 @Id @Column(name="CLIENTID")
 @GeneratedValue(generator="foreign")
 @GenericGenerator(name="foreign", strategy = "foreign", parameters={ @Parameter(name="property", value="client") })
 public Long getId() {
 return id;
 }
 @OneToOne(mappedBy="drivingDistance")
 public ClientVO getClient()
 {
 return client;
 }
}

If I try to assign a driving distance to the client and save it:

ClientVO client=(ClientVO)q.getSingleResult();


 DrivingDistanceVO vo2=new DrivingDistanceVO();
 //vo2.setId(new Long(225415));
 vo2.setLocation1(new Long(48254));
 vo2.setLocation2(new Long(171767));
 vo2.setUriString("http://www.google.com/intl/en_ALL/images/logo.gif");
 if (client.getDrivingDistance()==null)
 {
 client.setDrivingDistance(vo2);
 em.merge(client);
 }

I get the following error:

javax.persistence.PersistenceException: org.hibernate.id.IdentifierGenerationException: attempted to assign id from null one-to-one property: client
 at org.hibernate.ejb.AbstractEntityManagerImpl.throwPersistenceException(AbstractEntityManagerImpl.java:567)
 at org.hibernate.ejb.AbstractEntityManagerImpl.merge(AbstractEntityManagerImpl.java:210)
 at com.idfbins.nexus.business.test.ClientDrivingDistanceTest.testClientDriveDistancePersist(ClientDrivingDistanceTest.java:63)
Caused by: org.hibernate.id.IdentifierGenerationException: attempted to assign id from null one-to-one property: client
 at org.hibernate.id.ForeignGenerator.generate(ForeignGenerator.java:44)
 at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:98)
 at org.hibernate.event.def.DefaultMergeEventListener.entityIsTransient(DefaultMergeEventListener.java:165)
 at org.hibernate.event.def.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:102)
 at org.hibernate.event.def.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:51)
 at org.hibernate.impl.SessionImpl.fireMerge(SessionImpl.java:679)
 at org.hibernate.impl.SessionImpl.merge(SessionImpl.java:663)
 at org.hibernate.impl.SessionImpl.merge(SessionImpl.java:667)
 at org.hibernate.ejb.AbstractEntityManagerImpl.merge(AbstractEntityManagerImpl.java:201)
 ... 22 more
... Removed 21 stack frames

I have poured over the documentation and forums but can't understand why this is failing. I have seen others ask similar questions, but have not found any answers. I have noticed that if I call em.persist instead of em.merge I do not get this error. However, I thought that since the client already exists in the database that merge would be the appropriate method to call.

So, can anyone explain why I am getting the message "org.hibernate.id.IdentifierGenerationException: attempted to assign id from null one-to-one property: client
" even after I have assigned the driving distance to the client ( client.setDrivingDistance(vo2);
)