/**
  * Class constructor
  * 
  * @param resource &$db reference to the database handler
  * @param integer project identifier
  */
 function __construct(&$db, $tproject_id)
 {
     // you would think we could inherit the parent $db declaration
     // but it fails to work without this.
     $this->db =& $db;
     // instantiate the parent constructor.
     parent::__construct($this->db);
     $this->cf_map = $this->get_linked_cfields($tproject_id);
 }