Hibernate: select category0_.id as id0_, category0_.name as name0_, category0_.description as descript3_0_, category0_.icon as icon0_, category0_.tags as tags0_, category0_.parent as parent0_ from Categories category0_ where category0_.parent is null
ERROR - failed to lazily initialize a collection of role: es.bytelecom.wicketiki.objects.Category.children, no session or session was closed
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: es.bytelecom.wicketiki.objects.Category.children, no session or session was closed
        at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:358)
        at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationExceptionIfNotConnected(AbstractPersistentCollection.java:350)
        at org.hibernate.collection.AbstractPersistentCollection.readSize(AbstractPersistentCollection.java:97)
        at org.hibernate.collection.PersistentBag.size(PersistentBag.java:225)
        at wicket.markup.html.list.ListView.getViewSize(ListView.java:220)
        at wicket.markup.html.list.ListView.internalOnAttach(ListView.java:536)
        at wicket.Component.internalAttach(Component.java:2572)
        at wicket.MarkupContainer.internalAttach(MarkupContainer.java:341)
        at wicket.MarkupContainer.internalAttach(MarkupContainer.java:354)
        at wicket.Page.renderPage(Page.java:383)
        at wicket.protocol.http.WebRequestCycle.redirectTo(WebRequestCycle.java:160)
        at wicket.request.target.component.PageRequestTarget.respond(PageRequestTarget.java:60)
        at wicket.request.compound.DefaultResponseStrategy.respond(DefaultResponseStrategy.java:49)
        at wicket.request.compound.AbstractCompoundRequestCycleProcessor.respond(AbstractCompoundRequestCycleProcessor.java:66)
        at wicket.RequestCycle.doProcessEventsAndRespond(RequestCycle.java:902)
        at wicket.RequestCycle.processEventsAndRespond(RequestCycle.java:929)
        at wicket.RequestCycle.step(RequestCycle.java:1010)
        at wicket.RequestCycle.steps(RequestCycle.java:1084)
        at wicket.RequestCycle.request(RequestCycle.java:454)
        at wicket.protocol.http.WicketServlet.doGet(WicketServlet.java:219)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
        at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:368)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
        at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:869)
        at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:664)
        at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
        at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
        at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
   
    <session-factory>
       
        <!-- Database connection settings -->
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost/wicketiki</property>
        <property name="connection.username">root</property>
        <property name="connection.password">******</property>
       
        <!-- JDBC connection pool (use the built-in) -->
        <property name="connection.pool_size">1</property>
       
        <!-- SQL dialect -->
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
       
        <!-- Enable Hibernate's automatic session context management -->
        <property name="current_session_context_class">thread</property>
       
        <!-- Disable the second-level cache  -->
        <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>
       
        <!-- Echo all executed SQL to stdout -->
        <property name="show_sql">true</property>
       
        <mapping class="es.bytelecom.wicketiki.objects.Category" />
        <mapping class="es.bytelecom.wicketiki.objects.User" />
        <mapping class="es.bytelecom.wicketiki.objects.Page" />
       
    </session-factory>
   
</hibernate-configuration>

/**
* Entity class Category
*
* @author Juan
*/
@Entity()
@Table(name = "Categories")
@NamedQueries( {
    @NamedQuery(name = "Category.findById", query = "SELECT c FROM Category c WHERE c.id = :id"),
    @NamedQuery(name = "Category.findByName", query = "SELECT c FROM Category c WHERE c.name = :name"),
    @NamedQuery(name = "Category.findByDescription", query = "SELECT c FROM Category c WHERE c.description = :description"),
    @NamedQuery(name = "Category.findByIcon", query = "SELECT c FROM Category c WHERE c.icon = :icon"),
    @NamedQuery(name = "Category.findByTags", query = "SELECT c FROM Category c WHERE c.tags = :tags"),
    @NamedQuery(name = "Category.findByParent", query = "SELECT c FROM Category c WHERE c.parent = :parent")
})
public class Category implements Serializable {
   
   
    public static List<Category> getRootCategories() {
       
        List<Category> categories = new ArrayList<Category>();
       
        Session session = HibernateUtil.getCurrentSession();
        session.beginTransaction();
        categories = (List<Category>) session.createQuery("from Category c where c.parent is null").list();
        session.getTransaction().commit();
        return categories;
       
    }
   
   
   
   
    @ManyToMany(
    cascade={CascadeType.PERSIST, CascadeType.MERGE},
            targetEntity=Page.class
            )
            @JoinTable(
    name="CategoriesPages",
            joinColumns={@JoinColumn(name="categoryid")},
            inverseJoinColumns={@JoinColumn(name="pageid")}
    )
    private List<Page> pages;
   
    @Id
    @Column(name = "id")
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Integer id;
   
    @Column(name = "name")
    private String name;
   
    @Column(name = "description")
    private String description;
   
    @Column(name = "icon")
    private String icon;
   
    @Column(name = "tags")
    private String tags;
   
   
    @OneToMany(mappedBy="parent")
    private List<Category> children;
   
    @ManyToOne
    @JoinColumn(name="parent")
    @NotFound(action=NotFoundAction.IGNORE)
    private Category parent;
 
    // Contructors, getters and setter
 
}

/*
* HibernateUtil.java
*
* Creado el 17 de febrero de 2007, 16:00
*
* To change this template, choose Tools | Template Manager
* and open the template in the editor.
*/

package es.bytelecom.wicketiki;

import es.bytelecom.wicketiki.objects.Category;
import java.io.File;
import org.apache.log4j.LogManager;
import org.apache.log4j.Logger;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.cfg.Configuration;

/**
*
* @author Juan
*/
public class HibernateUtil {
   
    private static Logger log = LogManager.getLogger(HibernateUtil.class);
    private static SessionFactory sessionFactory;
   
    public static void configure(String hibernateXmlCfgFile) {
        try {
            // Create the SessionFactory from hibernate.cfg.xml
            sessionFactory = new AnnotationConfiguration().configure(new File(hibernateXmlCfgFile)).buildSessionFactory();
        } catch (Throwable ex) {
            // Make sure you log the exception, as it might be swallowed
            log.error("Initial SessionFactory creation failed.", ex);
            throw new ExceptionInInitializerError(ex);
        }
               
    }
   
    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
   
   
    public static void saveOrUpdate(Object o) {
        Session session = sessionFactory.getCurrentSession();
        session.beginTransaction();
        session.saveOrUpdate(o);
        session.getTransaction().commit();
    }
   
   
    public static void delete(Object o) {
        Session session = sessionFactory.getCurrentSession();
        session.beginTransaction();
        session.delete(o);
        session.getTransaction().commit();
    }
   
    public static Session getCurrentSession() {
        return sessionFactory.getCurrentSession();
    }
   
}

    @OneToMany(mappedBy="parent", fetch=FetchType.EAGER)
    private List<Category> children;