Paginator and LazyInitializationException

[agori]

Look at this use case:

...
@Scope(SESSION)
class UserList {
  @DataModel List<User> users;
  @Factory("users") void loadUsers() {
    users = em.createQuery(...).getResultList();
  } 
}

<h:dataTable value="#{users}" var="user" rows="10">
  <h:column>#{user.roles}</h:column>
  ... 
</h:dataTable>
<rich:datascroller .../>

If I have 20 users, then first page is ok. If I click to next I get an hibernate exception: LazyInitializationException.

This happens because my entities are detached and the roles collection can't be initialized.

The first solution is to loop on collection an initialize every entity:

@Factory("users") void loadUsers() {
  users = em.createQuery(...).getResultList();
  for (User u : users) {
    Hibernate.initialize(u.getRoles());
  }
} 

But if I have 10000 users I don't want to do this operation for every user. It kills performance.

So what is the best solution in this scenario? Note that I don't want to change UserList scope. Its scope is session and  not conversation or view.

[ivan.indrawan]

You can try to use a join fetch mechanism when you do the query.

http://docs.jboss.org/hibernate/stable/entitymanager/reference/en/html/queryhql.html

[agori]

Ivan Sukianto wrote on Jan 14, 2010 18:38:


You can try to use a join fetch mechanism when you do the query.

http://docs.jboss.org/hibernate/stable/entitymanager/reference/en/html/queryhql.html

Your solution is better but is not much different. The best solution should fetch only the elements appearing the the page, and not the whole list at creation time.

[lvdberg]

Hi,

Seam has some very nice Components of which the Query objects contain the stuff that you want. It paginates and by using join fetching in your query you get the roles you want.

Leo