Hello,

I need to know if the order of created events for collection, such as PostCollectionUpdateEvent is determinable.

Let me draw my scenario:

I've got a collection that represents a unidirectional one-to-many relationship, a classic parent/child relationship.

I'd would create the parents p1 and p2.
And the child c1 and c2.
and define the relations p1 -> c1 and p2 -> c2
and flush()

now, if I remove c1 from p1 and add to p2, I'd get a PostCollectionUpdateEvent for p1 and one for p2 noticing the removal or adding.

Is the order of this events deterministic?

For this events Hibernate would generate SQL statments like followings :

update simpleChild set id_parent=null where id_parent=? and id_simplechild=?
update simpleChild set id_parent=? where id_simplechild=?

Do they always have the same order?

Thanks for any hints

Kuno

Hi,

I assume that the order is deterministic.
Take a look at the implementation of org.hibernate.engine.ActionQueue.java and convince yourself:
the collection updates are enqueued into a ArrayList with the add method,
which appends the specified element to the end of this list.
The executeAction method then performs the actions in the same order as they were enqueued.



Exception is when a collection is created or removed. These actions are enqueued in separate arraylists
(see lines abobe).

Hi,

thanks for your reply. I'd like to explain my problem more precisely, since I think my question wasn't very clear.

I need to reproduce every db change to a journaling system using the hibernate events.

In the draw scenario below, hibernate would create two collection events, since there are two modified collections.

For event 1, it would do following
update simpleChild set id_parent=null where id_parent=1 and id_simplechild=1

For event 2, it would do following
update simpleChild set id_parent=2 where id_simplechild=1

The journaling system doens't allow conditionals for foreign keys like id_parent. For this reason, the order of event 1 and event 2 is important. Otherwise, I'd risk to overwrite the changed foreign key with null.

Therefore, I need to know if the order of those events is always like above or if it could also be reversed. Later would mean an unvalid journal entry.

I guess such a order isn't garantied, since this would mean that the action queue would be ordered according to the dependency hierarchy.


Thanks a lot.

Kuno

The order of collection-update events is chronologic and therefore deterministic
and given that you:

1.) remove c1 from p1

and then

2.) add c1 to p2

then you will have the SQL-statements executed in the order as you reported.
There's no need to be ordered according to the dependency hierarchy.

Guenther

Hello,

I cannot control how the changes are reported on hibernate API, since the developers are working in different departments. Therefore, for my needs the behavior should be independent on the report order.

Futhermore, I noticed that your conclusion about ordering was not excactly right. In my tests I found out, that the order depends on the order the entities are loaded in the session. Following would reverse the order:
parent2 = (SimpleParent) session.get(SimpleParent.class, idParent2);
parent1 = (SimpleParent) session.get(SimpleParent.class, idParent1);

Anyway, the current behavior is not deterministic in the way I'd like to use it.

Thanks a lot for your help.

Kuno

Sorry Kunt,

I was wrong with my presumption.
I oversight that the collection updates are not enqueued immediately,
apparently the are enqueued during flush where the chronologic order is'nt guaranteed anymore.