I am new to Hibernate/Spring and I have been running into alot of hibernate problems as I am reworking some code. Specifically with LazyInitializiationExpeception errors. Basically, we have a query layer that initializes query objects and them passes them back to all different parts of the infrastructure. The problem that I keep running into is that after the query objects are passed back I get "LazyInitializiationExpeception - could not initialize proxy - the owning session was closed" errors. From reading online I understand that this is occurring because the the lazy fetches are out of scope of the session. My question is for large infrastructures what is the common design approach to having sessions alive, or is there a way to address lazy fetching (besides switching to eager fetching) between different sessions?

Also what precisely are the scoping requirements for when an object can still reach the session?

thanks

For a servlet layer type app, see the Open Session in View pattern, often done with Spring. Outside of that, you often know the problem spots and can call something like this on the Collections contents as used:

session.lock(obj, LockMode.NONE);
Hibernate.initialize(obj)

Another alternative is to skip lazy altogether on your Collections and load everything "eagerly" , ie "lazy=false" .

Except for debugging purposes I don't want to just switch over to eager fetching, because I have nested data structures that I don't want it to eager fetch. I will check out the Open Session in View pattern. Thanks.

iksrazal: Does your session.lock example basically perform an eager fetch for a specific retrieval?

My hope is that there is a design pattern for large infrastructures as to where sessions and DAOs should get created and/or kept open?

No, but the question isn't really correct AFAIK. All it does is re-attach the Object to the hibernate session, so further processing can continue. Where lazy errors typically happen in my experience is from the Set etc side of a one-to-many, on the individual Objects. Eager will load the whole collection as its queried.