Hibernate session in RequestFactory

Hello,
I have a problem with RequestFactory and Hibernate session.
[hibernate.LazyInitializationException] - failed to lazily initialize
a collection of role: app.server.dao.HierarchyImpl.children, no
session or session was closed

@OneToMany(cascade = CascadeType.ALL)
@JoinTable(name = "HIERARCHY_RELATE", joinColumns =
{ @JoinColumn(name = "parent_id") }, inverseJoinColumns =
{ @JoinColumn(name = "child_id") })
public Set<HierarchyImpl> getChildren() {
return children;
}

public static List<HierarchyImpl> rootHierarchyRequest() {
int i = 0;
try {
SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
Session session = sessionFactory.openSession();
List<HierarchyImpl> hList = new ArrayList<HierarchyImpl>(session
.createQuery("from Hierarchy where parent is null").list());
session.close();
return hList;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
Adding FetchType.EAGER helps but in long terms will not solve my
problem.
Is there a good way to manage Hibernate session by RequestFactory?

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