In my DAO I use a convention where a method starting with load returns a persistent object and a method starting with find returns a non-persistent object (i.e. a 'safe to alter'/'readonly' one).

Currently I am implementing the find style methods using session.evict(object).

However, this has the following problem:

If I load a persistent object and alter it, but then subsequently find the same object (as part of a list returned by a general query, for example), my changes to the persistent object have been lost - my find has evicted it from the session cache and therefore made in non-persistent.

I am trying to find a better solution. I need to be able to supply both persistent and non-persistent copies of an object within the scope of a transaction, without them interfering with each other. I want to keep the solution as close to Hibernate as possible to avoid polluting business logic.

So far I see 3 options:

Make all classes in my model Cloneable, then get the find methods to supply clones. I guess this would work, but it means polluting my model, and all the objects I find will still end up in the session cache.

Try to keep a copy of the session cache, so I know which objects the find methods should evict. I have my doubts that the API exists to get my fingers deep enough into Hibernate b to do this. Also, this seems pretty ugly to me.

Run two sessions in parallel for each unit of work, one for getting persistent objects, the other for getting non-persistent objects. The readonly session would be FlushMode.NEVER, and then clear it's cache just before flushing and closing. However, I assume for these two sessions to play nicely, they would require two separate JDBC connections. I imagine my WebLogic 8.1 would supply these transparently, but I have just doubled the number of connections I require.

My questions are:

What are other people's experiences with this issue (a requirement to get both a persistent and a non-persistent copy of a object out of Hibernate in a single unit of work)?

Which solution do experienced Hibernators recommend? Or is there a better one out there?

Thanks very much ...

I use Hibernate until my business process implementation boundaries. Then I close the session. Have a look at the Thread Local session pattern in the wiki area.

I'm doing exactly that: hanging on to a session in a ThreadLocal, initialising and closing it at business process boundaries (these happen to be stateless session bean calls).

Can I get a non-persistent object out of a session?

I can't map it as read only, because sometimes I want to update it.

I can't evict() it because it might already exist (and be dirty) in the session cache.