Question

Few facts regarding the setup:

• It’s a Tomcat based app (althoug the issues arise outside Tomcat’s context as well – JUNIT)
• Not using Spring
• Every thread has its own Hibernate Session (at TLS)
• Objects are being saved/loaded in a mixed way, i.e ObjA may be created by thread A and later be manipulated by thread B and even later be updated by thread A and yet again be manipulated by thread Z but this time using HQL!

Having the above setup I’m getting errors such as:

• org.hibernate.HibernateException: illegally attempted to associate a proxy with two open Sessions
• org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect)

My understanding is that

• It’s all related to Hibernate’s Session, being that a session “owns” the objects “attached” to it (those it created/loaded)
• AND POSSIBLY an issue of caching

The question is obvious:

• Am I understanding the core issue (above)?
• How do I avoid such issues?
• Is there a rule of thumb that would help avoid these issues?
• Would using Spring help solving it (be a bit specific about it please)?
• Would detaching from Session every object after fetching it from the datastore, and attaching it to a Session later just before updating it would be the ideal way to handle it?

I could of course avoid all of it if I’d use only one Session object but that sounds so… blocking (thread-wise).

I’m sure these sort of issues were solved long time ago, just need to find it (without re-inventing the wheel).

Answer 1

Calling clear() before fetching the object(s).