m:n relations

[Lars Soltau <la...@slab.de>]

I have the following problem with m:n relations:

I have a bidirectional m:n relation, like the one in the tutorial, and 
when I try to store objects, the record in the intermediate table gets 
added twice, resulting in a duplicate key exception.

Here is my repository definition:

  <class-descriptor class="de.dmc.vms.Promotion" table="Promotion">
    <field-descriptor name="id" column="id" jdbc-type="INTEGER"
      primarykey="true" autoincrement="true"/>

    <collection-descriptor name="clients" 
element-class-ref="de.dmc.vms.Client"
      collection-class="java.util.ArrayList" 
indirection-table="Promotion_Client"
      auto-retrieve="true" auto-update="true" auto-delete="true"  
    >
      <fk-pointing-to-this-class column="promotionId"/>
      <fk-pointing-to-element-class column="clientId"/>
    </collection-descriptor>

  </class-descriptor>


  <class-descriptor class="de.dmc.vms.Client" table="Client">
    <field-descriptor name="id" column="id" jdbc-type="INTEGER"
      primarykey="true" autoincrement="true"/>

    <collection-descriptor name="promotions" 
element-class-ref="de.dmc.vms.Promotion"
      collection-class="java.util.ArrayList" 
indirection-table="Promotion_Client"
      auto-retrieve="true" auto-update="true" auto-delete="true"  
    >
      <fk-pointing-to-this-class column="clientId"/>
      <fk-pointing-to-element-class column="promotionId"/>
    </collection-descriptor>
  </class-descriptor>


The three tables are defined pretty straightforward. Here is the code to 
add new objects:

      // Build some example objects.
      Promotion promo1 = new Promotion("promo1");
      Promotion promo2 = new Promotion("promo2");
      Client client1 = new Client("client1");
      Client client2 = new Client("client2");
     
      // Connect the objects.
      promo1.addClient(client1);
      promo2.addClient(client1);
      promo2.addClient(client2);
     
      // Store the objects.
      broker.beginTransaction();
      broker.store(promo1);
      broker.store(promo2);
      broker.commitTransaction();

At this point I get a duplicate key exception, and tracing the SQL 
statements with P6Spy I see that the same INSERT INTO promotion_client 
occurs twice, with the columns switched:

INSERT INTO Promotion_Client (clientId,promotionId) VALUES ('222','442')
INSERT INTO Promotion_Client (promotionId,clientId) VALUES ('442','222')

What did I do wrong?

Thanks for your help.

Greetings
Lars Soltau