Hi,

Having a superclass Employee and a subclass ContentProducer mapped
through the "table per subclass" mapping strategy, I cast an Employee
instance to a ContentProducer and tried to save the resulting object
using the saveOrUpdate method(), but with no success.

What happened, I guess, is that at first Hibernate was unable to save
the ContentProducer because of the existing Employee with the same id
in the CONTENT_PRODUCER table. And when trying to update the same
ContentProducer it fails due to the lack of a content producer with
the same id in the CONTENT_PRODUCER table.

The problem is explicited when this exception is raised:

java.lang.IllegalArgumentException: attempt to create saveOrUpdate event with null entity
at org.hibernate.event.SaveOrUpdateEvent.<init>(SaveOrUpdateEvent.java:40)
at org.hibernate.event.SaveOrUpdateEvent.<init>(SaveOrUpdateEvent.java:23)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:480)

Thought I could solve it by changing the mapping stategy to the
"hierarchy per table"; but I´m really lost!

Any ideas?

If you have an Employee instance, then you should try to save it as an Employee instance. Downcasting is dangerous in Hibernate, because of the proxies.

Hope that helps!

Liem