TransientObjectException - hibernate

org.hibernate.TransientObjectException: object references an unsaved transient instance – save the transient instance before flushing: com.swacorp.pcs.common.model.ServiceLevel
<class name=”com.xxx.A” table=”A” schema=”TESTSCHEMA”>
<id name=”aId” type=”java.lang.Long”>
<column name=”A_ID” precision=”29? scale=”0? />
</id>
…………………..
some more mapping elements
…………………..
…………………..
<many-to-one name=”bId” class=”com.xxx.B” fetch=”select”>
<column name=”B_ID” precision=”29? scale=”0? />
</many-to-one>
…………………..
A is referring to B using a primary key column of bId of B.
In that post I have mentioned that if B is a transient object and you don’t want to persist the value of B to A then just tell the hibernate to ignore that value by saying
update=”false” insert=”false” in the many to one mapping.
But what if you want to persist the value of foreign key in A.
Then the approach is different. You have to make sure that instance B is persistent not transient.
That is if your code says something like
A a = new A();
B b = new B();
a.setB(b);
…..
…..
session.save(a);
you are in trouble. Because B is in transient state. You have to attach b to the session.
There may be other ways of attaching this transient object to session. The approach I am following is simple. I am reading the value of B from the database using Hibernate. That way, hibernate attaches B to session and it is then a persistent object.
That is I do something like
A a = new A();
B b = session.get(B.class, new Long(1));
a.setB(b);
…..
…..
session.save(a);
Hibernate defines and supports the following object states:

  * Transient :- an object is transient if it has just been instantiated using the new operator, and it is not associated with a Hibernate Session. It has no persistent representation in the database and no identifier value has been assigned.

  * Persistent :- a persistent instance has a representation in the database and an identifier value. It might just have been saved or loaded, however, it is by definition in the scope of a Session.

  * Detached :- a detached instance is an object that has been persistent, but its Session has been closed. The reference to the object is still valid, of course, and the detached instance might even be modified in this state. A detached instance can be reattached to a new Session at a later point in time, making it persistent again.

My changes:
HibernateTemplate template = getHibernateTemplate();
   Session session = template.getSessionFactory().getCurrentSession();
   itmAndPaxItmEvntOccrs.paxItm.setSvcLvl((ServiceLevel)session.get(itmAndPaxItmEvntOccrs.paxItm.getSvcLvl().getClass(), new Long(1)));
   template.saveOrUpdate(itmAndPaxItmEvntOccrs.paxItm);