Thread: [Hibernate-issues] [Hibernate-JIRA] Closed: (HB-533) Bidirectional Parent / Child relationship betwe

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Message:

   The following issue has been closed.

   Resolver: Gavin King
       Date: Tue, 9 Dec 2003 4:26 PM

You have one instance variable which is used by to two different properties, one on the superclass, one on the subclass.

Please use the user forum for these kind of problems. JIRA is for bugs in Hibernate.
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View the issue:

  http://opensource.atlassian.com/projects/hibernate/secure/ViewIssue.jspa?key=HB-533

Here is an overview of the issue:
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        Key: HB-533
    Summary: Bidirectional Parent / Child relationship between a class and a joined-subclass gets deleted by saveOrUpdate
       Type: Bug

     Status: Closed
   Priority: Minor
 Resolution: REJECTED

    Project: Hibernate2
 Components: 
             core
   Versions:
             2.1 rc1

   Assignee: Gavin King
   Reporter: Gary Miller

    Created: Tue, 9 Dec 2003 8:50 AM
    Updated: Tue, 9 Dec 2003 4:26 PM
Environment: JDK 1.4.0-b92
postgres 7.3.4

Description:
The child to parent reference get set to null when an existing graph is retrieved from the DB and then saveOrUpdate is called with no changes made to the graph.

The following example illustrates the point.

There is a work around which is to effectively disable the setParent method if the parent provided is null. This section of code is commented out in the example.

I have run this code up in a debugger but don't know how to debug a cglib generated class. 

I new to hibernate, please let me know how I could have improved my post.

Regards
Gary Miller

Class hierarchy
     Model
       |
   ---------
   |       |
  Root   NodeElem
            |
        -----------
        |          |
       Node       Leaf

Object Graph
  root -> nodes 
  node -> nodeelems
All these relationships are bidirectional
Therefore a node's parent can either be a Root or a NodeElem.

Mapping File test.hbm.xml
<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 2.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>
    <class name="net.sf.hibernate.examples.Root" table="eg_root" dynamic-update="false" dynamic-insert="false">
        <id name="id" column="id" type="java.lang.String" unsaved-value="null">
            <generator class="uuid.hex"/>
        </id>
        <version name="version" type="int" column="version"/>
        <bag name="nodes" lazy="false" inverse="true" cascade="save-update">
            <key column="root_id"/>
            <one-to-many class="net.sf.hibernate.examples.Node"/>
        </bag>
    </class>

    <class name="net.sf.hibernate.examples.NodeElem" table="eg_nodeelem" dynamic-update="false" dynamic-insert="false">
        <id name="id" column="id" type="java.lang.String" unsaved-value="null">
            <generator class="uuid.hex"/>
        </id>
        <version name="version" type="int" column="version"/>
        <many-to-one name="parentNodeElem" column="node_id" not-null="false" cascade="save-update"/>

        <joined-subclass name="net.sf.hibernate.examples.Node" table="eg_node" dynamic-update="false" dynamic-insert="false">
            <key column="id"/>
            <many-to-one name="parentRoot" column="root_id" not-null="false" cascade="save-update"/>
            <bag name="nodeElem" table="NodeElem" lazy="false" inverse="true" cascade="save-update">
                <key column="node_id"/>
                <one-to-many class="net.sf.hibernate.examples.NodeElem"/>
            </bag>
        </joined-subclass>

        <joined-subclass name="net.sf.hibernate.examples.Leaf" table="eg_leaf" dynamic-update="false" dynamic-insert="false">
            <key column="id"/>
            <property name="name" type="java.lang.String" update="true" insert="true" column="name"/>
        </joined-subclass>
    </class>
</hibernate-mapping>

Test Classes
sf.net.hibernate.example.Main
-----------------------------
package net.sf.hibernate.examples;

import java.util.Iterator;

import net.sf.hibernate.Query;
import net.sf.hibernate.Session;
import net.sf.hibernate.SessionFactory;
import net.sf.hibernate.Transaction;
import net.sf.hibernate.cfg.Configuration;
import net.sf.hibernate.cfg.Environment;

/**
 * @author garym
 * Main
 */
public class Main {

    static void print( Root r ) {
        System.out.println( r );
        for( Iterator it = r.getNodes().iterator() ; it.hasNext() ; ) {
            Node n = (Node) it.next();
            recurseNode( n , "\t" );
        }
    }

    static void recurseNode( Node n , String pretty ) {
        System.out.println( pretty + n.toString() + "\t parent:" + n.getParent() );
        for( Iterator it2 = n.getNodeElem().iterator(); it2.hasNext() ; ) {
            NodeElem ne = (NodeElem) it2.next();
            if( ne instanceof Node )
                recurseNode( (Node) ne , pretty + "\t" );
            else
                System.out.println( pretty + "\t" + ne.toString() + "\t parent:" + ne.getParent()  );
        }
    }

    public static void main(String[] args)
        throws Exception
    {
        SessionFactory sessionFactory =
            new Configuration()
                .configure( "/net/sf/hibernate/examples/hibernate.cfg.xml" )
//                .setProperty(Environment.HBM2DDL_AUTO, "create")
                .buildSessionFactory();
//
        for( int i = 0 ; i < 1 ; i++ ) {
            Session session = sessionFactory.openSession();
//
            Root r = null;
            Query query = session.createQuery("select r from Root as r");
            Iterator it = query.iterate();
            if( it.hasNext() ) {
                r = (Root) it.next();
                System.out.println("Retrieved" );
                Iterator it2 = r.getNodes().iterator();
                if( it2.hasNext() ) {
                    Node n = (Node) it2.next();
                    Node n2 = new Node();
                    n2.addNodeElem( new Leaf("new") );
                    n.addNodeElem( n2 );
                }
                print(r);

            } else {
                System.out.println("No Root found" );
                r = new Root();
                Node n = new Node();
                n.addNodeElem( new Leaf("Moe")   );
                n.addNodeElem( new Leaf("Curly") );
                n.addNodeElem( new Leaf("Larry") );
                r.addNode( n );
                print( r );
            }

            Transaction xaction= session.beginTransaction();
            System.out.println("Started Trans" );
            session.saveOrUpdate(r);
            System.out.println("Saved" );
            xaction.commit();
            System.out.println("Committed" );
            session.close();
        }
        sessionFactory.close();
    }
}

Model
-----
package net.sf.hibernate.examples;

/**
 * @author garym
 * Model
 */
public class Model
{
    String id;
    int ver;
    Model parent;

    void setParent( Model p ) {
// THIS IS THE WORK AROUND
//        if( p == null ) {
//////            parent = null;
//            return;
//        }
        if( parent != null && !p.equals(parent) )
            throw new RuntimeException("Parent can only be set twice \nthis:'"+this+"'\nparent:'" + p + "'");
        parent = p;
    }

    Model getParent( ) {
        return parent;
    }

    void setVersion( int v ) {
        ver = v;
    }
    int getVersion() {
        return ver;
    }

    void setId( String id ) {
        this.id = id;
    }
    String getId() {
        return id;
    }
}

Root
----
package net.sf.hibernate.examples;

import java.util.ArrayList;
import java.util.List;

/**
 * @author garym
 * Root
 */
public class Root
extends Model
{
    List nodes;

    Root() {};

    List getNodes() {
        return nodes;
    }

    void setNodes( List nodes ) {
        this.nodes = nodes;
    }

    void addNode( Node c ) {
        if(nodes == null) nodes = new ArrayList();
        nodes.add(c);
        c.setParent( this );
    }

//    public String toString() {
//        return nodes == null ? "[]" : nodes.toString();
//    }
}

NodeElem
--------
package net.sf.hibernate.examples;

/**
 * @author garym
 */
public class NodeElem
extends Model
{
    void setParentNodeElem( NodeElem p ) {
        setParent(p);
    }
    NodeElem getParentNodeElem() {
        return (NodeElem) getParent();
    }
}

Node
----
package net.sf.hibernate.examples;

import java.util.ArrayList;
import java.util.List;

/**
 * @author garym
 */
public class Node
extends NodeElem
{
    List nodeElems;

    Node() {};

    void setParentRoot( Root p ) {
        setParent(p);
    }
    Root getParentRoot() {
        Model p = getParent();
        if( p instanceof Root )
            return (Root) p;
        return null;
    }

    NodeElem getParentNodeElem() {
        Model p = getParent();
        if( p instanceof NodeElem )
            return (NodeElem) p;
        return null;
    }

    List getNodeElem() {
        return nodeElems;
    }

    void setNodeElem( List nodeElems ) {
        this.nodeElems = nodeElems;
    }

    void addNodeElem( NodeElem c ) {
        if(nodeElems == null)
            nodeElems = new ArrayList();
        nodeElems.add(c);
        c.setParent( this );
    }

//    public String toString() {
//        return nodeElems == null ? super.toString() + "[]" : super.toString() + nodeElems.toString();
//    }
}

Leaf
----
package net.sf.hibernate.examples;

/**
 * @author garym
 * Child
 */
public class Leaf
extends NodeElem
{
    String name;
    Leaf() {}

    Leaf( String name  ) {
        setName(name);
    }

    void setName( String name ) {
        this.name = name;
    }

    String getName() {
        return name;
    }

    public String toString() {
        return "name:'" + name + "'";
    }
}

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