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I use hibernate with web application, when i open many session begin the problems with update and save. this is the information:

[b]Hibernate version: I used hibernate 3

[b]Code between sessionFactory.openSession() and session.close():

session = HibernateSessionFactory.currentSession();
tx = session.beginTransaction();
session.update(nuevo);
session.flush();
tx.commit();


[b]Full stack trace of any exception that occurs:

org.hibernate.HibernateException: illegally attempted to associate a proxy with two open Sessions
at org.hibernate.proxy.AbstractLazyInitializer.setSession(AbstractLazyInitializer.java:68)
at org.hibernate.engine.PersistenceContext.reassociateProxy(PersistenceContext.java:520)
at org.hibernate.engine.PersistenceContext.unproxyAndReassociate(PersistenceContext.java:565)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:65)
at org.hibernate.impl.SessionImpl.update(SessionImpl.java:499)
at org.hibernate.impl.SessionImpl.update(SessionImpl.java:490)
at com.vinculolegal.servicio.ServicioBD.update(ServicioBD.java:809)
at com.vinculolegal.action.IndicadorAction.execute(IndicadorAction.java:94)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:484)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:237)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:214)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:198)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:152)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:137)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:118)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:102)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:929)
at org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:160)
at org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:300)
at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:374)
at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:743)
at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:675)
at org.apache.jk.common.SocketConnection.runIt(ChannelSocket.java:866)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:683)
at java.lang.Thread.run(Thread.java:534)




[b]Name and version of the database you are using: Postgres database 8.0

Where do you close your session?

Its necesary close the session ? when i open the current session?

Like that:


session = HibernateSessionFactory.currentSession();
tx = session.beginTransaction();
session.update(nuevo);
session.flush();
tx.commit();

--->>>> session.close();


the session dont lost?

Thanks

It depends on what you are trying to do.

I'm not sure why you got that Exception, but this is something to think about.

Are you using the Thread local session? In other words, in your hibernate.cfg.xml do you have:



If so, then each thread has it's own copy of the Session. In a web application , the web container has a pool of threads handling requests. Each will have it's own Hibernate Session. If you are storing hibernate managed objects in the HTTP Session and then trying to update your database, you aren't guarenteed subsequent HTTP requests will be handled by the same servlet thread and thus the same Hibernate Session.

Let me know if this isn't clear. But I suspect you may be storing objects in the HTTP Session and then trying to update them in a different servlet thread.

Yes, I load one object and save in the session HTTP: request.getSession().setAttribute("obj", obj);

In the three next servlet, i update the object and throw the exception, how i manage this situation? what is the best way to do that.

Thanks.

I've just started using Hibernate 3 in a web environment so takes these as suggestions.

1. I've read that some people put the hibernate Session into the HTTP Session and then retrieve it in the next request. The only problem I see with this is that the session could have a lot of stuff cached in it and you may run into memory problems. But that depends on your applicaiton. you could always evict() objects from the cache or close the session at certain points. The Hibernate Wiki has a section on "Long Running Conversations" that's probably worth reading. Also see the "Open Session In View" pattern on the Wiki.

2. Another option is to disconnect the objects from the hibernate session, put them in the HTTP Session, and then reattach them. Your best bet here is to read the Hibernate document on disconnecting and reattaching objects. I think it's short. This isn't much work and might be a good option.

3. A third option is to just do a database hit when the new HTTP request comes in and get a new copy of the object, modify that, and persist it. In this case you would store just the unique identifier in the HTTP session since you don't need the whole object.

There's probably some other ways, but hopefully this will give you some ideas. Sorry I don't have a definitive answer. I've basically been using the 3rd option, but my web app is very simple, with few users, and a low volume of requests (at least for now).