/**
  * Gets all the not mandatory relationship roles. That is, the roles where the target is one, and
  * all the corresponding foreign key columns are nullable.
  *
  * @todo perhaps we need to iterate over all columnmaps?
  * @return The MandatoryRelationshipRoles value
  */
 public Collection getNotMandatoryRelationshipRoles() {
   CompositePredicate notMandatory = new Not();
   notMandatory.add(middlegen.predicates.relation.Mandatory.getInstance());
   return getRelationshipRoles(notMandatory);
 }
 /**
  * Gets all the mandatory relationship roles. That is, the roles where the target is one, and at
  * least one of the corresponding foreign key columns are not nullable.
  *
  * @todo What if a mandatory relationship role has been disabled? Perhaps it shouldn't be possible
  *     to disable such mandatory roles in the GUI? -And warn the user if she tries to?
  * @todo perhaps we need to iterate over all columnmaps?
  * @return The MandatoryRelationshipRoles value
  */
 public Collection getMandatoryRelationshipRoles() {
   return getRelationshipRoles(middlegen.predicates.relation.Mandatory.getInstance());
 }