if I always use saveOrUpdate() is it ok? Hibernate will understand on its own that an object is new so it will persist it in the database
or an object exists in the database and it will updated?Does saveOrUpdate() covers both cases?

It is OK to use saveOrUpdate() exclusively as long as the unsaved-value of the primary key is set properly (default is usually sufficient).

Can you please give me an example?You mean in the mapping?

What about if I use save() and this object is already in the database.Will I have a exception?

OK, here goes.



The unsaved-value tells Hibernate that if the id is null, then the object should be considered transient (a new object) and that saveOrUpdate should save the new object via INSERT. If there is a value in the id property, then Hibernate should consider the object as persistent or detached (an object that already exists in the database) and that saveOrUpdate should save the object via UPDATE.

For most cases, the unsaved-value property default should suffice (the default unsaved-value for any Object is null, for primitives, it will be 0), and does not need to be specified in the mapping document explicitly.

And yes, if the object already exists in the database and you call save() it will throw an exception.

You are doing the rite thing .. the only case when you would want to use save is when you are expecting the object to be new ( you are expecting an exception when its already there )

so I should use the saveOrUpdate() right?Since the default is unsaved-value=null ?I mean I do not have to change anything else to use in both cases saveOrUpdate().

Correct.

Thank you very much