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LazyInitializationException - Hibernate

 
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All:

I am a newbie to Hibernate and am getting the following exception when trying to run a sample pgm from the Hibernate tutorial.Can anyone pl let me know on how to resolve this exception.

------------------------------------------------------------------------
[java] org.hibernate.LazyInitializationException: failed to lazily initiali
ze a collection of role: Person.events - no session or session was closed
[java] at org.hibernate.collection.AbstractPersistentCollection.throwLa
zyInitializationException(AbstractPersistentCollection.java:191)
[java] at org.hibernate.collection.AbstractPersistentCollection.initial
ize(AbstractPersistentCollection.java:183)
[java] at org.hibernate.collection.AbstractPersistentCollection.read(Ab
stractPersistentCollection.java:48)
[java] at org.hibernate.collection.PersistentSet.isEmpty(PersistentSet.
java:118)
[java] at EventManager.main(Unknown Source)
[java] Exception in thread "main"
[java] Java Result: 1
[echo] Executing
------------------------------------------------------------------------

part of the code in my main():
------------------------------------------------------------------------

mgr.addPersonToEvent(new Long(1), new Long(1));
mgr.addPersonToEvent(new Long(1), new Long(2));

List personList = mgr.listPersons();
for (int i = 0; i < personList.size(); i++)
{
Person person = (Person) personList.get(i);
Set eventSet = person.getEvents();
if (eventSet != null && !eventSet.isEmpty())
{
Iterator iter = eventSet.iterator();
while (iter.hasNext())
{
System.out.println("Event - " + ((Event)
iter.next()).getTitle());
}
}
}

private void addPersonToEvent(Long personId, Long eventId)
{
Session session = HibernateUtil.currentSession();
Transaction tx = session.beginTransaction();

Person aPerson = (Person) session.load(Person.class, personId);
Event anEvent = (Event) session.load(Event.class, eventId);
aPerson.getEvents().add(anEvent);

tx.commit();
HibernateUtil.closeSession();
}
 
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no session or session was closed


You need a open Session to get more data from the database. Either explicitly get the events association when you get your persons object, or access them from whithin an open session.
 
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I see a lot of people with this misunderstanding about Hibernate session. Many people are using in their web applications the SessionInView Pattern, opening the hibernate session before any jsp/java processing and closing it after having shown the jsp page. If you intend to use Struts, you can create a HibernateFilter. Search at google and you'll find some good examples.
 
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