hang on to lazy loading, but how?

TheStijn · **Joined:** Mon Nov 13, 2006 8:22 am **Posts:** 28

hi,

I have following mapping file:

Code:

<hibernate-mapping package="com.skopco.pronocl.data">
    <class name="Team" table="TEAM"> 
     ...
    <set name="users" table="USERTEAM">
         <key column="TEAM_ID"/>
        <many-to-many column="USER_ID" class="User" />
    </set>
...

Basically a team contains users.
Now, I'm loading all teams and for each team get all it's users:

Code:

List teams = dao.getTeams();
for (Iterator iterator = teams.iterator(); iterator.hasNext();)
{
   Team t = (Team) iterator.next();
   Set s = t.getUsers();
         
   for (Iterator iter2 = s.iterator(); iter2.hasNext();)
   {
      User u = (User) iter2.next();
...

I'll stop right there because this already throws an exception:
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.skopco.pronocl.data.Team.users, no session or session was closed

if I change the mapping file like this:

Code:

it works fine (obviously).

My question is, if I want to hang on to lazy loading (teams are loaded many times, it's users are only required now and then) then how can I load the team's users explicitly?
I could create an HQL-query which return the users by team-id but I'm sure there a 'hibernate-solution' for this.

many thanks for any help!

Stijn

MikePloed · **Posted:** Tue Nov 14, 2006 5:36 am

Y E S you definately want to hang to lazy loading. This exception occurred because you accessed a lazy collection after closing your session.

You have the following options:
Within the "lifetime" of your session you can preload the lazy collection with Hibernate.initialize(team.getUsers)

Again within the liftime of the session you can eagerly load the teams users with a left join fetch hql query

from Team t left join fetch t.users

TheStijn · **Joined:** Mon Nov 13, 2006 8:22 am **Posts:** 28

MikePloed wrote:

Y E S you definately want to hang to lazy loading. This exception occurred because you accessed a lazy collection after closing your session.

Thanks for your reply.

Sorry if this is a stupid question (hib-beginner) but when exactly is a session closed?
In this case I never do a close (or tx.commit); I load the teams and then try to get the users without closing the session. Or is the latter done automatically somehow? If so, when?

don't worry, won't forget your credits

MikePloed · **Posted:** Tue Nov 14, 2006 6:00 am

Can you please post the code of dao.getTeams() .. I think you close the session in there

TheStijn · **Joined:** Mon Nov 13, 2006 8:22 am **Posts:** 28

MikePloed wrote:

Can you please post the code of dao.getTeams() .. I think you close the session in there

Code:

public class TeamManager
{
   private TeamDAO dao = new TeamDAO();
   
   public List getAll()
   {
        Session session = HibernateUtil.getSessionFactory().getCurrentSession();
        
        session.beginTransaction();

        return dao.getAll(session);
}

Code:

public class TeamDAO
{
   public List getAll(Session session)
   {
      return session.createQuery("from Team").list();
   }
}

thanks,
Stijn

christian · **Posted:** Tue Nov 14, 2006 6:39 am

http://hibernate.org/42.html

TheStijn · **Joined:** Mon Nov 13, 2006 8:22 am **Posts:** 28

christian wrote:

http://hibernate.org/42.html

thanks,

I'll try out the session-per-conversation pattern but I still don't see when the session is closed in the code above. I never do a commit or flush between loading the teams and getting the users from a team?

TheStijn · **Joined:** Mon Nov 13, 2006 8:22 am **Posts:** 28

Quote:

this might work fine when running with servlets but what about unit-testing? You can't use servlet-filters in that case. My unit-test for this action also fails (same exception).

you may discard this, stupid question

regards,
Stijn