Hibernate: OneToMany save children by cascade

Question

In the class Parent there is a list List. When the parent is saved the children which have been added or changed shall be save / updated by hibernate.

I've found many explanations on this, however, I just don't get it to work.

Parent.class try A

@Entity
public class Parent {
// id and other attributes
@OneToMany(mappedBy = "parent")
@org.hibernate.annotations.Cascade(org.hibernate.annotations.CascadeType.ALL)
protected List<child> children;

Parent.class try B

@Entity
public class Parent {
// id and other attributes
  @OneToMany(mappedBy = "parent", cascade = { javax.persistence.CascadeType.ALL },
 orphanRemoval = true)
 @org.hibernate.annotations.Cascade({ 
 org.hibernate.annotations.CascadeType.PERSIST,
 org.hibernate.annotations.CascadeType.MERGE,
 org.hibernate.annotations.CascadeType.REFRESH,
 org.hibernate.annotations.CascadeType.SAVE_UPDATE,
 org.hibernate.annotations.CascadeType.REPLICATE,
 org.hibernate.annotations.CascadeType.LOCK,
 org.hibernate.annotations.CascadeType.DETACH })
protected List<child> children;

children are added to a new parent. Afterwards both are saved by

sessionFactory.getCurrentSession().saveOrUpdate(parent);

when flushing, though, I get the following error:

org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: de.pockettaxi.backend.model.ride.RideSingle
at org.hibernate.engine.ForeignKeys.getEntityIdentifierIfNotUnsaved(ForeignKeys.java:243)
at org.hibernate.type.EntityType.getIdentifier(EntityType.java:456)
at org.hibernate.type.ManyToOneType.isDirty(ManyToOneType.java:265)
at org.hibernate.type.ManyToOneType.isDirty(ManyToOneType.java:275)
at org.hibernate.type.TypeHelper.findDirty(TypeHelper.java:295)
at org.hibernate.persister.entity.AbstractEntityPersister.findDirty(AbstractEntityPersister.java:3378)
at org.hibernate.event.def.DefaultFlushEntityEventListener.dirtyCheck(DefaultFlushEntityEventListener.java:520)
at org.hibernate.event.def.DefaultFlushEntityEventListener.isUpdateNecessary(DefaultFlushEntityEventListener.java:230)
at org.hibernate.event.def.DefaultFlushEntityEventListener.onFlushEntity(DefaultFlushEntityEventListener.java:154)
at org.hibernate.event.def.AbstractFlushingEventListener.flushEntities(AbstractFlushingEventListener.java:219)
at org.hibernate.event.def.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:99)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:50)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1216)

Does anybody see my mistake?

Thank you a lot!!

Answer 1

I guess if you answer the question from the first comment, we will come to this situation:

• you have an already persisted parent
• you have new child objects, that were not yet persisted
• you add the children to the parent and do saveOrUpdate

In that case hibernate just cascades the save or update to the children, but they cannot be saved or updated as they have not been persistent yet. And now Hibernate says simply "I cannot update a non persistent entity"

In one sentence: Hibernate only cascades what it is issued to cascade. In this case you issue a "SAVE_UPDATE", which is cascaded then further to the children. I guess you expected Hibernate to be smart and switch to persist for the children here. But this is not how Hibernate works here, I came across similar situations before, too. A bit confusing, but if you once got how cascading works, you will see such situations.