Greetings.

I started a similar discussion long time ago and would like to summarize everything in a new thread.

My application is using a single session, which cache gets cleared every now and then to avoid performance problems.

Here is a scenario that results in NonUniqueObjectException to be thrown when object A is saved:

1. Retrieve object A from the database
2. ... Do some heavy db stuff without changing A ...
3. Clear session cache (therefore loose reference to A)
4. Retrieve object B, which references object A (causes A to be brought in the session cache again).
5. A.setProperty("foo")
6. Save A (Throws NonUniqueObjectException)

I have my own Broker and Transaction classes, which forward calls to the Hibernate classes. All my business queries and updates go through my two classes, so all updates are treated the same way.

I spent several hours reading this forum and trying all kinds of tricks, but to no vain. Could anyone please point me in the right direction.

Thanks.

Alec

This is anti-pattern, see "Session and Transaction scope" on the Wiki. Read Hibernate in Action for a very detailed discussion of application design.

Actually, there are certain, VERY specific use cases where a single long session is acceptable. Its arguably acceptable if you want desktop application style semantics. The application is then responsible for explicitly refresh()ing things.


In this case, you can use saveOrUpdateCopy() to avoid the NUOE.

I did order "Hibernate in Action", but haven't received it yet. So, meanwhile I would have to use this forum :)

It is not necessary for me to use a very long session, so I agree with Gavin that I may need to close and open the session every now and then.

But, this conflicts with the architecture that I want to use for my business layer. I want all database requests to go through my Broker class, which will delegate them them to the Hibernate broker. So, my broker class should be the only class dealing with Hibernate sessions and transactions. This means that I have only two options:

1. Have ALL requests processed within one session: open a session when the broker is initialized and clear it's cache to avoid performance problems

2. Have EACH request processed between: open a session when the broker method is called, process request, and close the session before returning

I am currently using the first approach, which results in NUOE.

Both of these options are considered as anti-paterns in Wiki "Session and Transaction scope". It seems that if I want to group multiple DB requests in one session I would need to put the opening and closing session logic in my presentation layer, which I don't think is a good idea.


Should I just switch to the second option or there are other ways to solve this without putting the Hibernate session logic in the presentation layer?

Thanks.

Alec

Gavin,

Do you have time too look at my issue? I think it's similair to this issue, but it's happening on a delete. Im using the ThreadLocal pattern from the documentation, as this will be a Tomcat hosted application. My issue is currently happening at the application facade level where I have all transactional scope.

Here's the original post.

http://forum.hibernate.org/viewtopic.php?t=933689

The problem with me is that I'm getting the exception on session.delete, not saveOrUpdate. Is there now a similair semantic?