problem with outer-join

abrol · **Joined:** Tue Apr 03, 2007 2:10 am **Posts:** 2

HI,

I have a small query. Although I have set the outer-join property of user in the Child class as "true", but when I retrieve the children of the Parent class it fails to eagerly fetch the user elements associated with the Child class. Can anyone help me with this?

Hibernate version:3.0

[b]Mapping documents:

Code:

[color=green]<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
          "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="org.hibernate.parentChild">
   <class name="Parent">
      <id name="id" column="PARENT_ID">
         <generator class="increment" />
      </id>

      <version name="version" type="long" />

      <property name="type" />

      <set name="children" cascade="all-delete-orphan" inverse="true">
         <key column="parent_id" />
         <one-to-many class="Child" />
      </set>
   </class>

   <class name="Child">
      <id name="id" column="CHILD_ID">
         <generator class="increment" />
      </id>

      <property name="schoolName" type="string" />

      <many-to-one name="user" column="USER_ID" class="Usr" cascade="all" [b]outer-join="true"[/b] />
      
   </class>

   <class name="Usr" table="USR">
      <id name="id" column="USER_ID">
         <generator class="increment" />
      </id>

      <property name="firstName" type="string" column="firstName" not-null="true" />

      <property name="lastName" type="string" column="lastName" not-null="false" />
   </class>

</hibernate-mapping>[/color]

Code between sessionFactory.openSession() and session.close():
package org.hibernate.parentChild;

Code:

import java.util.Iterator;
import java.util.List;
import java.util.Set;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.auction.HibernateUtil;
import org.hibernate.auction.User;

public class ParentManager {
   private Parent theParent;

   private void addParent() throws Exception {
      System.out.println("adding Parent ........");

      Session s = HibernateUtil.currentSession();
      Transaction tx = null;
      try {
         tx = s.beginTransaction();

         theParent = new Parent();
         Usr user = new Usr();
         user.setFirstName("first child's first name");
         user.setLastName("first child's last name");

         Child child = new Child();
         child.setUser(user);
         child.setSchoolName("first child's school name");
         theParent.addChild(child);

         child = new Child();
         user = new Usr();
         user.setFirstName("second child's first name");
         user.setLastName("second child's last name");
         child.setUser(user);
         child.setSchoolName("second child's school name");
         theParent.addChild(child);

         s.save(theParent);

         tx.commit();
      } catch (Exception e) {
         if (tx != null)
            tx.rollback();
         throw e;
      } finally {
         HibernateUtil.closeSession();
      }
   }

   private void getChildren() throws Exception{
      System.out.println("getting children......");

      Session s = HibernateUtil.currentSession();
      Transaction tx = null;
      try {
         tx = s.beginTransaction();

         List l = s.createQuery("from Child").list();
         tx.commit();
      } catch (Exception e) {
         if (tx != null)
            tx.rollback();
         throw e;
      }
   }

   public static void main(String[] args) throws Exception {
      final ParentManager test = new ParentManager();
      test.addParent();
      test.getChildren();
   }
}

The generated SQL (show_sql=true):
Hibernate: insert into Parent (version, type, PARENT_ID) values (?, ?, ?)
Hibernate: insert into USR (firstName, lastName, USER_ID) values (?, ?, ?)
Hibernate: insert into Child (schoolName, USER_ID, CHILD_ID) values (?, ?, ?)
Hibernate: insert into USR (firstName, lastName, USER_ID) values (?, ?, ?)
Hibernate: insert into Child (schoolName, USER_ID, CHILD_ID) values (?, ?, ?)
getting children......
Hibernate: select child0_.CHILD_ID as CHILD1_, child0_.schoolName as schoolName4_, child0_.USER_ID as USER3_4_ from Child child0_

Thanks in advance,
Ashish Abrol

gskempes · **Joined:** Mon Nov 22, 2004 11:21 am **Posts:** 42

Hello Ashish,
Hibernate uses lazy initialization for referenced objects by default. If you wish to change this behaviour, you have to turn it off. I recommend to turn it off only where absolutely needed, otherwise you may fetch a very large subset of your database with just one simply query.

In your example:

Code:

<many-to-one name="user" column="USER_ID" class="Usr" cascade="all" outer-join="true" lazy="false"/> 

Regards,
Georg

abrol · **Joined:** Tue Apr 03, 2007 2:10 am **Posts:** 2

Yes with Lazy="false" I am able to retrieve the User object also but does that mean whereever I have to use outer-join="true" then alzy must be set to false. Also by setting lazy ="false" and outer-join="true" I am achieving the same thing that could have been achieved with lazy ="false". Then what is the purpose of outer-join

gskempes · **Joined:** Mon Nov 22, 2004 11:21 am **Posts:** 42

Hello Ashish,

sorry, I had ignored your setting outer-join="true" because I never used it. By the way, is it the same as fetch="join"? I didn't find any documentation for a feature called outer-join="true". If you use lazy="false" you can specify whether one SQL is fired (fetch="join) or 2 sequential SQL's are fired (fetch="select") for initializing both objects.

Regards,
Georg

ashish261080 · **Joined:** Mon Mar 14, 2005 9:07 am **Posts:** 27

My query still remains unanswered.