CMR configuration confusion

[clive jordan]

Hi Guys,

Could someone explain what is happening here as I am not 100% sure of the exact mechanism in operation. I have the thing working OK but I had to configure things differently to how I was expecting. And no, I'm not using xdoclet as I want to understand what is going on!

I have two simple Entity Beans that represent these tables:

 create table movie
(
mid integer not null primary key,
titlevarchar,
gendre varchar,
did varchar
);
 
create table director
(
did integer not null primary key,
namevarchar,
oscars integer
); 

And there is a many to one relationship from movies to director.

- The Movie Bean has a remote interface which the client talks to.
- The Director bean has only a local interface.

I have a Movie remote Home business method:

public String[] listMovieByDirector( int did ) throws FinderException, RemoteException;

I have setup a CMR in the configuration files and all works fine.

Here is my ejb-jar.xml file:

 <?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE ejb-jar PUBLIC "-//Sun Microsystems, Inc.//DTD Enterprise JavaBeans 2.0//EN" "http://java.sun.com/dtd/ejb-jar_2_0.dtd">
 
<ejb-jar>
   <enterprise-beans>
     <entity>
         <description>Entity7 Movie Bean</description>
         <ejb-name>Entity7MovieBean</ejb-name>
 <home>learnEJB.Entity7.Entity7MovieHome</home>
 <remote>learnEJB.Entity7.Entity7Movie</remote>
 <ejb-class>learnEJB.Entity7.Entity7MovieBean</ejb-class>
 <persistence-type>Container</persistence-type>
 <prim-key-class>java.lang.Long</prim-key-class>
 <reentrant>false</reentrant>
 <cmp-version>2.x</cmp-version>
 <abstract-schema-name>movieSchema</abstract-schema-name>
 <cmp-field>
 <field-name>mid</field-name>
 </cmp-field>
 <cmp-field>
 <field-name>title</field-name>
 </cmp-field> 
 <cmp-field>
 <field-name>gendre</field-name>
 </cmp-field>
 <primkey-field>mid</primkey-field>
 <query>
 <query-method>
<method-name>ejbSelectMovieByDirector</method-name>
<method-params>
<method-param>int</method-param>
</method-params>
</query-method>
<ejb-ql>
<![CDATA[
select m.title from movieSchema m
where m.director.did = ?1
]]>
</ejb-ql>
</query>
      </entity>
  
     <entity>
         <description>Entity7 Director Bean</description>
         <ejb-name>Entity7DirectorBean</ejb-name>
 <local-home>learnEJB.Entity7.Entity7DirectorLocalHome</local-home>
 <local>learnEJB.Entity7.Entity7DirectorLocal</local>
 <ejb-class>learnEJB.Entity7.Entity7DirectorBean</ejb-class>
 <persistence-type>Container</persistence-type>
 <prim-key-class>java.lang.Long</prim-key-class>
 <reentrant>false</reentrant>
 <cmp-version>2.x</cmp-version>
 <abstract-schema-name>directorSchema</abstract-schema-name>
 <cmp-field>
 <field-name>did</field-name>
 </cmp-field>
 <cmp-field>
 <field-name>name</field-name>
 </cmp-field> 
 <cmp-field>
 <field-name>oscars</field-name>
 </cmp-field>
 <primkey-field>did</primkey-field>
      </entity>
</enterprise-beans>

<relationships>
<ejb-relation>
<ejb-relation-name>Movie-Director</ejb-relation-name>
<ejb-relationship-role>
<ejb-relationship-role-name>Movie-has-Director</ejb-relationship-role-name>
<multiplicity>Many</multiplicity>
<cascade-delete/>
<relationship-role-source>
<ejb-name>Entity7MovieBean</ejb-name>
</relationship-role-source>
<cmr-field>
<cmr-field-name>director</cmr-field-name>
</cmr-field>
</ejb-relationship-role>
 
<ejb-relationship-role>
<ejb-relationship-role-name>Director-has-Movies</ejb-relationship-role-name>
<multiplicity>One</multiplicity>
<relationship-role-source>
<ejb-name>Entity7DirectorBean</ejb-name>
</relationship-role-source>
</ejb-relationship-role>
</ejb-relation>
</relationships>

<assembly-descriptor>
<container-transaction>
<method>
<ejb-name>Entity7MovieBean</ejb-name>
<method-name>*</method-name>
</method>
<trans-attribute>Required</trans-attribute>
</container-transaction>

<container-transaction>
<method>
<ejb-name>Entity7DirectorBean</ejb-name>
<method-name>*</method-name>
</method>
<trans-attribute>Required</trans-attribute>
</container-transaction>
</assembly-descriptor>
</ejb-jar> 

You can see the EJB-QL for the method:

 
select m.title from movieSchema m
where m.director.did = ?1 

The jbosscmp-jdbc.xml file is below:

  
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE jbosscmp-jdbc PUBLIC
   "-//JBoss//DTD JBOSSCMP-JDBC 4.0//EN"
   "http://www.jboss.org/j2ee/dtd/jbosscmp-jdbc_4_0.dtd">
 
<!-- ===================================================================== -->
<!--                                                                       -->
<!--  Overridden JBossCMP-JDBC Configuration                                 -->
<!--                                                                       -->
<!-- ===================================================================== -->
 
<jbosscmp-jdbc>
   <defaults>
      <datasource>java:/DefaultDS</datasource>
  <datasource-mapping>Hypersonic SQL</datasource-mapping>
      <create-table>false</create-table>
   </defaults>
   <enterprise-beans>
      <entity>
     <ejb-name>Entity7MovieBean</ejb-name>
 <table-name>movie</table-name>
 <cmp-field>
 <field-name>mid</field-name>
<column-name>mid</column-name>
 </cmp-field>
 <cmp-field>
 <field-name>title</field-name>
<column-name>title</column-name>
 </cmp-field>
 <cmp-field>
 <field-name>gendre</field-name>
<column-name>gendre</column-name>
 </cmp-field>
  </entity>
  
      <entity>
     <ejb-name>Entity7DirectorBean</ejb-name>
 <table-name>director</table-name>
 <cmp-field>
 <field-name>did</field-name>
<column-name>did</column-name>
 </cmp-field>
 <cmp-field>
 <field-name>name</field-name>
<column-name>name</column-name>
 </cmp-field>
 <cmp-field>
 <field-name>oscars</field-name>
<column-name>oscars</column-name>
 </cmp-field>
  </entity>  
   </enterprise-beans>
 
<relationships>
<ejb-relation>
<ejb-relation-name>Movie-Director</ejb-relation-name>
<foreign-key-mapping/>
<ejb-relationship-role>
<ejb-relationship-role-name>Movie-has-Director</ejb-relationship-role-name>
<key-fields/>
</ejb-relationship-role>
 
<ejb-relationship-role>
<ejb-relationship-role-name>Director-has-Movies</ejb-relationship-role-name>
<!-- 
I'm a little confused here. I would have thought that this mapping
would go on the other side of the relationship as we want to map the
foriegn key (did) to the  getDirector() CMR method in the MovieBean.
Jboss will not allow this for multiplicity of Many so we need to
put it on this side of the relationship.
-->
<key-fields>
<key-field>
<field-name>did</field-name>
<column-name>did</column-name>
</key-field>
</key-fields>
 
</ejb-relationship-role>
</ejb-relation>
</relationships>
 
</jbosscmp-jdbc>

The comment I have put in the above file explains my problem. It does not make too much sense that I have to define the foriegn-key mapping on the DirectorBean side of the relationship. As there are only two sides to the relationship, I guess Jboss can work it out but I don't understand the reasoning behind it.

Any pearls of wisdom out there ??

Thanks,
Clive