Head First EJB

Defining relationships in your abstract persistence schema (in the DD)

CMP field definitions are so easy. You declare a <cmp-field> and give it a name that matches one of your getter/setter pairs (following the naming rule of dropping the “get” and “set” and beginning the CMP field name with a lower-case letter).

But CMR is more involved. You can’t be in a relationship with only yourself, so a relationship always includes two beans!

1. Define an ejb-relation between two beans

   Note

   Every relationship has exactly two beans.

   1. Define an ejb-relationship-role for one bean

      1. multiplicity for this bean

         Note

         Multiplicity of this bean (i.e. how many of this type will the OTHER participant have)

      2. source for this bean

         Note

         Which bean are we really talking about?

      3. cmr-field for this bean

         Note

         Must match the “virtual field” in the bean class

      4. cascade-delete for this bean

         Note

         Only if THIS bean wants to be deleted when its partner is deleted.

   1. Define an ejb-relationship-role for the second bean

      1. multiplicity for this bean

      2. source for this bean

      3. cmr-field for this bean

      4. cascade-delete for this bean

         Note

         Same stuff for the second participant in the relationship

Relationship definition for the Director-to-Movie relationship

1. Define an ejb-relation between two beans

   <ejb-relation>

   Note

   Each <ejb-relation> describes one pair of beans... one relationship. They REALLY should have named this <ejb-relationship>

   1. Define an ejb-relationship-role for ...