parent/child cmp2 relationship

[dward2]

Does anyone have any good design pointers on a cmp2 entity which has one cmr parent and also 0 to many cmr children of the same type as it is? Any examples?

The ejb-jar.xml doesn't seem too hard in that respect but the jbosscmp-jdbc.xml file seems limiting in that on deployment, jboss doesn't let me specify keyfields for both roles in the relationship. Of course, mabye my design is flawed and I won't have to.

Thanks for any and all help, sharing experiences, etc.

[objectwizatlycos]

Hi David,

I have managed to code this and I can deploy it. However, once deployed, if I call setParent() or addChild() on my bean, the relationships are not maintained (though the same code works in Orion server). I've included my jbosscmp-jdbc.xml in case it helps. If you can get it working - or even if you can't - perhaps between us we can make it work!! ;-)

Regards,

Peter.

<INCLUDED TEXT>

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE jbosscmp-jdbc PUBLIC "-//JBoss//DTD JBOSSCMP-JDBC 3.0//EN" "http://www.jboss.org/j2ee/dtd/jbosscmp-jdbc_3_0.dtd">

<jbosscmp-jdbc>

java:/DefaultDS
<datasource-mapping>Hypersonic SQL</datasource-mapping>


<enterprise-beans>


<ejb-name>forum/Message</ejb-name>
<create-table>true</create-table>
<remove-table>true</remove-table>
<read-only>true</read-only>
<time-out>100</time-out>
<table-name>message</table-name>

<cmp-field>
<field-name>children</field-name>
<column-name>children</column-name>

</cmp-field>
<cmp-field>
<field-name>id</field-name>
<column-name>id</column-name>

</cmp-field>
<cmp-field>
<field-name>parent</field-name>
<column-name>parent</column-name>

</cmp-field>
<cmp-field>
<field-name>subject</field-name>
<column-name>subject</column-name>

</cmp-field>
<cmp-field>
<field-name>text</field-name>
<column-name>text</column-name>

</cmp-field>
<!--
To define load groups for this entity, write a file named
jbosscmp-jdbc-load-MessageBean.xml and put it in
your mergedir. Write it according to the following DTD slice:
<!ELEMENT load-groups (load-group+)>
<!ELEMENT load-group (load-group-name, description?, field-name+)>
<!ELEMENT load-group-name (#PCDATA)>
<!ELEMENT description (#PCDATA)>
<!ELEMENT field-name (#PCDATA)>
<!ELEMENT eager-load-group (#PCDATA)>
<!ELEMENT lazy-load-groups (load-group-name+)>
-->



</enterprise-beans>


<ejb-relation>
<ejb-relation-name>parent</ejb-relation-name>
<foreign-key-mapping/>
<ejb-relationship-role>
<ejb-relationship-role-name>children</ejb-relationship-role-name>
<key-fields>
<key-field>
<field-name>id</field-name>
<column-name></column-name>
</key-field>
</key-fields>
</ejb-relationship-role>
<ejb-relationship-role>
<ejb-relationship-role-name>parent</ejb-relationship-role-name>
<key-fields/>
</ejb-relationship-role>
</ejb-relation>


<dependent-value-classes>

</dependent-value-classes>

</jbosscmp-jdbc>

[dward2]

Though I think I found the right way to do it a while ago, I've negleted to share what I've learned with the community. (bad me.) So here goes (granted, I haven't tested this completely yet, but it's looking good so far)...

If you want a bidierectional parent-child relationship where both the parent and the child are of the same bean, *you have to define two relationships, not one*:

- The first specifies the one-2-one unidirectional relationship an entity has with its parent. This will correlate with an abstract get/setParent(YourBeanLocal) in the bean.

- The second specifies the one-2-many unidirectional relationship an entity has with its children. This will correlate with an abstract get/setChildren(Collection) in the bean.

It seems impossible to do this bidirectionaly in a single relationship definition.

Here is an "Album" example:

<!-- ejb-jar.xml snippet -->
<ejb-relation>
<ejb-relation-name>Album-AlbumChildren</ejb-relation-name>
<ejb-relationship-role>
<ejb-relationship-role-name>
Album-Has-AlbumChildren
</ejb-relationship-role-name>
One
<relationship-role-source>
<ejb-name>Album</ejb-name>
</relationship-role-source>
<cmr-field>
<cmr-field-name>children</cmr-field-name>
<cmr-field-type>java.util.Collection</cmr-field-type>
</cmr-field>
</ejb-relationship-role>
<ejb-relationship-role>
<ejb-relationship-role-name>
AlbumChildren-For-Album
</ejb-relationship-role-name>
Many
<cascade-delete/>
<relationship-role-source>
<ejb-name>Album</ejb-name>
</relationship-role-source>
</ejb-relationship-role>
</ejb-relation>
<ejb-relation>
<ejb-relation-name>Album-AlbumParent</ejb-relation-name>
<ejb-relationship-role>
<ejb-relationship-role-name>
Album-Has-AlbumParent
</ejb-relationship-role-name>
One
<relationship-role-source>
<ejb-name>Album</ejb-name>
</relationship-role-source>
<cmr-field>
<cmr-field-name>parent</cmr-field-name>
</cmr-field>
</ejb-relationship-role>
<ejb-relationship-role>
<ejb-relationship-role-name>
AlbumParent-For-Album
</ejb-relationship-role-name>
One
<relationship-role-source>
<ejb-name>Album</ejb-name>
</relationship-role-source>
</ejb-relationship-role>
</ejb-relation>

<!-- jbosscmp-jdbc.xml snippet -->
<ejb-relation>
<ejb-relation-name>Album-AlbumParent</ejb-relation-name>
<foreign-key-mapping/>
<ejb-relationship-role>
<ejb-relationship-role-name>
Album-Has-AlbumParent
</ejb-relationship-role-name>
<key-fields>
<key-field>
<field-name>key</field-name>
<column-name>PARENT_KEY</column-name>
</key-field>
</key-fields>
</ejb-relationship-role>
<ejb-relationship-role>
<ejb-relationship-role-name>
AlbumParent-For-Album
</ejb-relationship-role-name>
<key-fields/>
</ejb-relationship-role>
</ejb-relation>
<ejb-relation>
<ejb-relation-name>Album-AlbumChildren</ejb-relation-name>
<relation-table-mapping>
<table-name>ALBUM_CHILDREN</table-name>
</relation-table-mapping>
<ejb-relationship-role>
<ejb-relationship-role-name>
Album-Has-AlbumChildren
</ejb-relationship-role-name>
<key-fields>
<key-field>
<field-name>key</field-name>
<column-name>PARENT_KEY</column-name>
</key-field>
</key-fields>
</ejb-relationship-role>
<ejb-relationship-role>
<ejb-relationship-role-name>
AlbumChildren-For-Album
</ejb-relationship-role-name>
<key-fields>
<key-field>
<field-name>key</field-name>
<column-name>CHILD_KEY</column-name>
</key-field>
</key-fields>
</ejb-relationship-role>
</ejb-relation>

[dward2]

After working with Dain on the jboss-user list, he seems to think that it should be possible to do a same-bean parent/child relationship with just one cmr-rel, not two. Though I know how to represent this in a database easily enough, I can't figure out how to do it properly in the xml. Dain said he is looking into putting together an example for us. :)

[stephenbibby]

I dont know if anyone is interested in this anymore, or infact if they are using XDoclet to generate the parent/child relationship, but I came across the same problem (Project EJB has a child/parent relationship with itself).

I found a solution by using XDoclet to generate the relationships. It detects that the relationship is bi-directional and creates a child/parent relationship that works (for JBoss 3.0). The following is the XDoclet tags, and generated deployment descriptors. I hope this helps.

/**
* Get the parent project.
*
* @ejb:interface-method view-type="local"
* @ejb:relation name="Project-ParentProject"
* role-name="one-Project-belongs-to-one-Project"
* target-role-name="one-Project-has-many-Project"
* target-multiple="yes"
*
* @jboss:relation related-pk-field="name"
* fk-column="parentProject"
*/
public abstract com.dca.timesheet.beans.ejb.ProjectEJBLocal getParentProject();

/**
* This sets a parent project
*
* @ejb:interface-method view-type="local"
*/
public abstract void setParentProject(com.dca.timesheet.beans.ejb.ProjectEJBLocal parent);

/**
* Gets child projects.
*
* @ejb:interface-method view-type="local"
* @ejb:relation name="Project-ParentProject"
* role-name="one-Project-has-many-Project"
* target-role-name="one-Project-belongs-to-one-Project"
*
*/
public abstract Collection getChildProjects();

/**
* Sets child projects.
*
* Mutator for the virtual relationship field.
*
* @ejb:interface-method view-type="local"
*/
public abstract void setChildProjects(Collection childProjects);

These XDoclet tags generate lots of output, but the important stuff is here...
jbosscmp-jdbc.xml:
<ejb-relation>
<ejb-relation-name>Project-ParentProject</ejb-relation-name>
<foreign-key-mapping/>
<ejb-relationship-role>
<ejb-relationship-role-name>one-Project-has-many-Project</ejb-relationship-role-name>
<key-fields>
<key-field>
<field-name>name</field-name>
<column-name>parentProject</column-name>
</key-field>
</key-fields>
</ejb-relationship-role>
<ejb-relationship-role>
<ejb-relationship-role-name>one-Project-belongs-to-one-Project</ejb-relationship-role-name>
<key-fields/>
</ejb-relationship-role>
</ejb-relation>

and in ejb-jar.xml:
<ejb-relation >
<ejb-relation-name>Project-ParentProject</ejb-relation-name>
<!-- bidirectional -->
<ejb-relationship-role >
<ejb-relationship-role-name>one-Project-has-many-Project</ejb-relationship-role-name>
One
<relationship-role-source >
<ejb-name>ProjectEJB</ejb-name>
</relationship-role-source>
<cmr-field >
<cmr-field-name>childProjects</cmr-field-name>
<cmr-field-type>java.util.Collection</cmr-field-type>
</cmr-field>
</ejb-relationship-role>
<ejb-relationship-role >
<ejb-relationship-role-name>one-Project-belongs-to-one-Project</ejb-relationship-role-name>
Many
<relationship-role-source >
<ejb-name>ProjectEJB</ejb-name>
</relationship-role-source>
<cmr-field >
<cmr-field-name>parentProject</cmr-field-name>
</cmr-field>
</ejb-relationship-role>
</ejb-relation>