Hi,

I have the following problem and I hope someone can provide me some hints or a solution.

I have an entity with a composite id containing a string and a counter.
The entity is called order. The key contains the section for this order and an incremental counter.
Like this:

Order (entity)
|- OrderPK (Serializable)
…..|- Section (String)
…..|- Id (Long)


On my normal entities I let the database increment the counter with <generator class=”increment”/>. However this is not a possible solution as the Id should be incremented for each section (to see how many orders for this selection were made already).


The only way I see currently is to load the last number from the database (for example by select max(..)….) and increment it in my own business code and save the new order.

And here comes my questions:

1) is there an easier solution than mine

2) which possibilities do I have to avoid problems with concurrent threads? (Let’s say worker A reads the last number for section “france” and worker B does the same exactly the same moment. Both sessions increase the counter by one and try to save their new orders. The second one will get an exception.)


Any help would be great.


Best regards
Tom

I am afraid there is no easier solution. See these, they may give you some pointers.
http://opensource.atlassian.com/project ... e/HHH-2060
http://forum.hibernate.org/viewtopic.php?p=2374438


I think in a loop you can keep on trying incrementing the count till the save is successful.

As always great and fast support here ;-)

I can see I have to increment my counter "by hand".

I'm currently thinking of introducing a persistence class with section and current counter in it.
I could query that class with hibernate and increment its counter.
So I don't have to use max(..) in my query.

One additional question there:
what does Session.lock do and could I use it for the concurrenxcy problem?

Maybe I could avoid the concurrent problem by simply locking the persistence class which holds my counter value.
I would update the counter and write the change to database.

But I'm not sure how it is technically handled by hibernate. Are database locks used and what happens in clustered environments.


best regards
tom