Hi
I have a question of the right usage of entity manager (EM).

i have a complex entity that contains list of sub entities.
i want to implement manual commit thingy. so i pesrsist entities then somewhere afterwards i do either em.flush() or em.getTransaction().rollback().

but something is wrong here for me.

when i create entity manager, should i do em.getTransaction().beginTransaction()?

when i try to persist the complex object, the list of sub objects is being emptied in the proccess. Doesnt it persist i nrecursion for sub entities too?
Even if i persist the sub entities first it still empties my list... on the complex persist..

in addition there is em.getTransaction().commit(); should i use it instead of em.flush() or not?

thanks.
Hope to get understand what is the right thing to do ...

First of all, my suggestion is you create a unit test and find out yourself. You can see what Hibernate is doing by following the SQL logs.

Secondly, for any modifications to be actually committed you need to begin a transaction and commit it. "flush()" just tells Hibernate to issue the SQL commands, it does not do a commit to the database.

I read in the api that flush synchronizing stuff to the database.

Anyway i am doing em.getTransaction().begin()
and em.getTransaction().commit();

My question is what shall i do with persist() it wont persist my sub objects.
(even when they are already managed)

p.s.
i got unit testing, it doesnt help me to understand the concept