Hibernate saveOrUpdate behavior

Question

Does anyone know how Hibernate knows whether to INSERT or to UPDATE a value in the database when session.saveOrUpdate() is called?

So far, I have only determined that it is not dependent on the information in the cache, and that the existence of the entity in the database is determined by the primary key.

Answer 1

When you use .saveOrUpdate() Hibernate will check if the object is transient (it has no identifier property) and if so it will make it persistent by generating it the identifier and assigning it to session. If the object has an identifier already it will perform .update().

From the documentation:

saveOrUpdate() does the following:

• if the object is already persistent in this session, do nothing
• if another object associated with the session has the same identifier, throw an exception
• if the object has no identifier property, save() it
• if the object's identifier has the value assigned to a newly instantiated object, save() it
• if the object is versioned by a "version" or "timestamp", and the version property value is the same value assigned to a newly instantiated object, save() it otherwise update() the object