public function getCollaboration($con = null)
 {
     if ($this->aCollaboration === null && $this->collaboration_id !== null) {
         include_once 'lib/model/om/BaseCollaborationPeer.php';
         $this->aCollaboration = CollaborationPeer::retrieveByPK($this->collaboration_id, $con);
     }
     return $this->aCollaboration;
 }