How Do I Solve this kind of exception: Illegally attempted to associate a proxy with two open Sessions.

For each thread i have a own session. Must i go work with versioning?

Great question - I'm having the same problem. My unit tests are failing with this error, but it doesn't always happen consistently.

I'm using the Castle.Facilities.NHibernateIntegration.NHibernateFacility to manage sessions.

-dave

Did you figure out a good way to solve this? I am having the same problem!

If I'm not mistaken, this exception is caused if you try to pass an entity that is persistent in one session to another session associated with the same SessionFactory.

If you have a separate session per thread then it sounds like you are passing entities between your threads. If you need to do this you should evict the object from the first session before passing it to the second session.

Cheers,

Symon.

Thank you for you answer!

Actually my problem is the following. I have a multi threaded application. Therefore concurrent threads need access to the NHibernate Sessions. I tried using one Session, reconnecting and disconnecting but this caused the threads to wait for access to the single Session.

The solution was to create a Session for every transaction and release it right after the end of the transaction.

The problem with this is that I can't use lazy load, since an entity is never associated with a Session.

What is the best way to create Sessions in an application like this?

Thanks again!

Rogerio

ISessions are explicitly not thread safe. There are loads of discussions about the way to manage sessions on the web and this forum; personally I prefer very short session lifetimes and specifying what you want up front. So one approach would be to use very short session lifetimes and specify what you want before releasing the session. Obviously it kind of depends on whether true lazy loading is useful to you; in our case we're generally able to specify up front which bits of the model we're likely to need in a given case.

Thanks Steve,

Do you have any reference of where to read more about how to manage sessions?!

Thanks again!

Rogério

No; I've pieced things together from Google - do a search for 'manage hibernate sessions' or something similar. There are a load of blog entries on how different people have gone about doing this. It seems to be the biggest single question people ask so perhaps at some point there'll be some official documentation on it.

I think many peoples' usage is slightly different from others. Creating sessions isn't expensive, so the simplest way to solve your problem would be to create a new one whenever you need one. If you need them to stick around (maybe keep a session per thread over the lifetime of the application, and connect/disconnect as you've already tried), how about (sort of psuedo code):



You'd probably want to add some thread safety to that. HTH.

Hi Steve,

I had tried something like what you suggested. But then I get into the problem of having one entity associated with more than one ISession.
I guess the ISession management depends too much on how the application is designed.

Thank you for your quick answers!

Rogério

That sounds really dangerous - editing the same thing from multiple threads is always going to cause you problems, even without Hibernate. Without really knowing what you're trying to achieve I don't know if I can help much more. If the threading is because you have CPU intensive processing tasks I'd suggest doing the DB access in one thread to simplify things. you can't use one ISession from multiple threads (without locking) and you can't use the same entity in multiple ISessions so you're kind of between a rock and a hard place.