public function applyData ( $data = NULL ) {
        parent::applyData( $data );
        if ($data != null) {
            self::$propData[$this->getKey()] = $this;
            self::$keyCache[$this->getClassKey()] = $this->__keyName;
            $key = $this->__keyName;
            self::$__ids[$this->getClassKey()][$this->$key] = true;
        }
    }