Trivial problem with bidirectional list

thea · **Joined:** Tue Apr 19, 2005 2:58 am **Posts:** 4

I need some help getting a bidirectional list to work, I probably made a trivial mistake somewhere but I can't figure it out.

The code below works fine when using <set> in the mappings and Set and HashSet instead of List in the java code, however I need to have the children in their order which is not supported by <set>. So I tried to use the <list> tag which is now supported for bidirectional lists in Hibernate3.

The child table contains the "pos" column but all rows contain 0. When reading in, only one child is retrieved, not both.

Please advise what I have to do so that the pos column contains the index of my list.

I have omitted all constructors, getters and setters as they were generated by Eclipse.

Hibernate version: version 3.0 (28.2.2005)

Parent.hbm.xml:

Code:

<?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="sample">
    <class name="Parent" table="parent">
        <id name="id" type="long">
            <generator class="increment"/>
        </id>
        <property name="name" type="string"/>
       <list name="children" inverse="true" cascade="all-delete-orphan">
          <key column="parent_id"/>
          <list-index column="pos"/>
          <one-to-many class="Child"/>
       </list>
    </class>
</hibernate-mapping>

Child.hbm.xml:

Code:

<?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="sample">
    <class name="Child" table="child">
        <id name="id" type="long">
            <generator class="increment"/>
        </id>
        <property name="name" type="string"/>
        <property name="pos" type="integer"/>
        <many-to-one name="parent" column="parent_id" not-null="true"/>
    </class>
</hibernate-mapping>

Class Parent.java:

Code:

package sample;

import java.util.ArrayList;
import java.util.List;
import java.util.Set;
import java.util.HashSet;


public class Parent {

   private Long   id;
   private String   name;
   private List   children   = new ArrayList();

        // constructors, getters, setters generated by Eclipse,
        // omitted here

   public void addChild(Child child) {

      children.add(child);
      child.setParent(this);
   }

   public void removeChild(Child child) {

      if (children.remove(child))
         child.setParent(null);
   }
}

Class Child.java:

Code:

package sample;


public class Child {

   private Long   id;
   private int      pos;
   private String   name;
   private Parent   parent;

        // constructors, getters, setters generated by Eclipse,
        // omitted here
}

Main:

Code:

package sample;

import java.util.Iterator;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.cfg.Environment;


public class TestList {

   public static void main(String[] args) {

      Parent parent = new Parent();
      parent.setName("Parent");

      Child child1 = new Child();
      child1.setName("Child 1");
      parent.addChild(child1);
      Child child2 = new Child();
      child2.setName("Child 2");
      parent.addChild(child2);

      for (Iterator iter = parent.getChildren().iterator(); iter.hasNext();) {
         Child child = (Child) iter.next();
         System.out.println(child.getName());
      }

      try {
         Configuration cfg = new Configuration();
         cfg.addClass(Parent.class);
         cfg.addClass(Child.class);
         cfg.setProperty(Environment.HBM2DDL_AUTO, "create");
         cfg.setProperty("hibernate.show_sql", "true");

         SessionFactory sf = cfg.buildSessionFactory();
         Session s = sf.openSession();
         Transaction tx = s.beginTransaction();

         s.save(parent);
         tx.commit();
         s.flush();
         s.close();
         s = null;
         sf.close();
         sf = null;
         cfg = null;

      } catch (Exception e) {
         System.out.println("Exception in Hibernate:" + e.getMessage());
      }

      try {
         Configuration cfg = new Configuration();
         cfg.addClass(Parent.class);
         cfg.addClass(Child.class);
         cfg.setProperty("hibernate.show_sql", "true");

         SessionFactory sf = cfg.buildSessionFactory();
         Session s = sf.openSession();
         Transaction tx = s.beginTransaction();

         Parent newParent = (Parent) s.load(Parent.class, new Long(1));
         for (Iterator iter = newParent.getChildren().iterator(); iter.hasNext();) {
            Child child = (Child) iter.next();
            System.out.println(child.getName());
         }

         tx.commit();
         s.flush();
         s.close();
         s = null;
         sf.close();
         sf = null;
         cfg = null;


      } catch (Exception e) {
         System.out.println("Exception in Hibernate:" + e.getMessage());
      }
   }
}

Name and version of the database you are using: MySQL 4.0.20

anthony · **Posted:** Tue Apr 19, 2005 4:40 am

http://www.hibernate.org/193.html

thea · **Joined:** Tue Apr 19, 2005 2:58 am **Posts:** 4

thanks a lot, will try this.

Is that the official way to do it in Hibernate3?

http://forum.hibernate.org/viewtopic.php?t=938636 mentions the article you suggested too, but gavin wrote that this problem is completely fixed in HB3. So I thought that was a workaround for Hibernate2, and there is a better solution for HB3 (which is what I am using).

anthony · **Posted:** Tue Apr 19, 2005 8:01 am

oh, i didn't know about it, have you tried with last release (3.01)?

thea · **Joined:** Tue Apr 19, 2005 2:58 am **Posts:** 4

It does not work with 3.0.1 either, but it works fine after adding

public int getRow()
{
return this.getParent().getChildren().indexOf(this);
}

as suggested in the article.

However:

The HB2 documentation says that 'Hibernate does not support bidirectional one-to-many associations with an indexed collection (list, map or array) as the "many" end'. This line has dropped from the HB3 documentation. See http://www.hibernate.org/hib_docs/refer ... irectional and http://www.hibernate.org/hib_docs/v3/re ... irectional.

So it certainly looks as if HB3 does, in fact, now supports bidirectional lists.
The HB3 docs do not mention special getters/setters as suggested in http://www.hibernate.org/193.html
special getters/setters seem to have problems, see the comment at the end of the article and also http://forum.hibernate.org/viewtopic.php?t=938636

So my conclusion is that this workaround is not the "official" way to do this in HB3. Or maybe I missed some crucial details from the HB3 documentation?

emmanuel · **Posted:** Wed Apr 20, 2005 7:07 am

Actually you'll need to update your mapping a bit

Code:

Parent
<list inverse="false"/>
</list>

Child
<many-to-one insert="false" update="false"/>

To summarize, you need to let the coçllection be the owner side.

anthony · **Posted:** Wed Apr 20, 2005 7:58 am

http://www.hibernate.org/193.html up to date

thea · **Joined:** Tue Apr 19, 2005 2:58 am **Posts:** 4

Works for me now, thanks. This should also go into the HB3 documentation, it seems not to be obvious for newbies.

emmanuel · **Posted:** Fri Apr 22, 2005 10:33 am

Year was not for me either ;-)
Open a jira improvement for that please.