I created two tables which are having many to many unidirectional relation, and also created join table.

The following are the mapping files for event and people classes.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.venkat.mtmbd.db">
<class name="Events" table="table_events">
<id name="eventId" type="integer">
<column name="EVENT_ID"/>
<generator class="native"/>
</id>
<property name="date" type="date">
<column name="EVENT_DATE" sql-type="timestamp"/>
</property>
<property name="eventTitle" type="string">
<column length="50" name="EVENT_TITLE"/>
</property>
<set name="persons" table="table_events_person" cascade="all">
<key column="EVENT_ID"/>
<many-to-many class="Person" column="PERSON_ID" />
</set>
</class>
</hibernate-mapping>
*******************************
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.venkat.mtmbd.db">
<class name="Person" table="table_person">
<id name="personId" type="integer">
<column name="PERSON_ID"/>
<generator class="native"/>
</id>
<property name="firstName" type="string">
<column length="30" name="FIRST_NAME"/>
</property>
<property name="lastName" type="string">
<column length="30" name="LAST_NAME"/>
</property>
<property name="age" type="integer">
<column name="AGE"/>
</property>
<set name="events" table="table_events_person" cascade="all">
<key column="PERSON_ID"/>
<many-to-many class="Events" column="EVENT_ID"/>
</set>
</class>
</hibernate-mapping>


My JSF is having two pages to create the data separately for event and participant tables.
when I am trying to delete the record for event table being in event page The following exception were thrown.


javax.faces.el.EvaluationException: org.hibernate.HibernateException: Illegal attempt to associate a collection with two open sessions
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:102)
at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102)
at javax.faces.component.UICommand.broadcast(UICommand.java:315)
at javax.faces.component.UIData.broadcast(UIData.java:912)
at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:775)
at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1267)
at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:82)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:312)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1523)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:279)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:188)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:641)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:97)
at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:85)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:185)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:332)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:233)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:165)
at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:791)
at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:693)
at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:954)
at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:170)
at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:135)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:102)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:88)
at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:76)
at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:53)
at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:57)
at com.sun.grizzly.ContextTask.run(ContextTask.java:69)
at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:330)
at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:309)
at java.lang.Thread.run(Thread.java:619)
Caused by: org.hibernate.HibernateException: Illegal attempt to associate a collection with two open sessions
at org.hibernate.collection.AbstractPersistentCollection.setCurrentSession(AbstractPersistentCollection.java:410)
at org.hibernate.event.def.OnUpdateVisitor.processCollection(OnUpdateVisitor.java:43)
at org.hibernate.event.def.AbstractVisitor.processValue(AbstractVisitor.java:101)
at org.hibernate.event.def.AbstractVisitor.processValue(AbstractVisitor.java:61)
at org.hibernate.event.def.AbstractVisitor.processEntityPropertyValues(AbstractVisitor.java:55)
at org.hibernate.event.def.AbstractVisitor.process(AbstractVisitor.java:123)
at org.hibernate.event.def.DefaultDeleteEventListener.onDelete(DefaultDeleteEventListener.java:101)
at org.hibernate.event.def.DefaultDeleteEventListener.onDelete(DefaultDeleteEventListener.java:52)
at org.hibernate.impl.SessionImpl.fireDelete(SessionImpl.java:766)
at org.hibernate.impl.SessionImpl.delete(SessionImpl.java:744)
at com.venkat.mtmbd.db.dao.EventsDao.delete(EventsDao.java:43)
at com.venkat.mtmbd.client.EventsManagedBean.deleteEvent(EventsManagedBean.java:149)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.sun.el.parser.AstValue.invoke(AstValue.java:234)
at com.sun.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:297)
at org.jboss.weld.util.el.ForwardingMethodExpression.invoke(ForwardingMethodExpression.java:43)
at org.jboss.weld.el.WeldMethodExpression.invoke(WeldMethodExpression.java:72)
at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:98)
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:88)
... 33 more