hello,
I have two basic questions regarding persistent objects:

Question 1:
I create a POJO of type A. After that, I create an arbitrary query.



The createQuery() causes Hibernate to flush. myPojo gets an ID assigned, but is apparently not persisted to the database. How come? Isn't flushing supposed to save the objects to the database?

Question 2:
Later in my code, I try to do saveOrUpdate() on myPojo.



Since myPojo already has an ID, I get an exception telling me I have a foreign-key problem (ORA-02291: integrity constraint xxx violated - parent key not found). myPojo contains collections of other POJOs, which Hibernate tries to save before myPojo, which is not possible.

I understand that setting the flushMode to COMMIT would be a workaround, but that is probably a bad solution as I suspect there is some other basic design flaw here...

If myPojo.id is null, everything goes fine. Could someone explain this behaviour, I would be very grateful.

cheers,
pj

You have to have more code than that....

Just creating a POJO that has a hibernate mapping will NOT generate an ID. It's not even associated with the Session at this point and therefore session.flush() will have no impact.

yes, myPojo does contain more data, but my id is null. When running createQuery(), myPojo gets an sequence-id from the database. Does this not mean that a flush is performed?

From "Hibernate in Action" (p. 160):
"Hibernate flushes occur only at the following times:

[...]
Sometimes before a query is executed
[...]

"

I believe this is what happens in my case, because when I set FlushMode.COMMIT, myPojo.id remains null.

/pj

If this is REALLY all you are doing...



The Hibernate session knows NOTHING about myPojo so has no reason/way to add an ID for it. Is there any code in your Constructor A() ?

There would have to be some code associating myPojo with the hibernate Session in between the
A myPojo = new A(); and the Query q= session.createQuery("from ....");

or it's definitely not Hibernate setting you're id.

yes, you are right. myPojo contains stuff like

B b = (B)session.load(B.class, id);
myPojo.setB(b);

Is this important? Because my question was why myPojo was not saved when Hibernate appears to do a flush(). Please enlighten me :-)

cheers,
pj

I can't "enlighten"you without all of the information.
http://www.hibernate.org/ForumMailingli ... AskForHelp

And even assuming the flush does send the changes to the database, you will still need to Commit them for them to be stored permanently. This is a database thing, not a hibernate thing.

well, it seems like you misunderstood my question, but you eventually answered my first question anyway. A flush() does not save to the database, I need to do a commit() as well (sic!). A very basic thing, of course, which I probably should have been aware of.

Any ideas for question 2?

cheers,
pj

The order in which child objects are saved is determined by the inverse="true/false" attribute on the collection mapping. So that is probably your problem.

posting your mapping files would help....