public function getMapBetweenObjects()
 {
     $map = array_merge(parent::getMapBetweenObjects(), self::$map_between_objects);
     foreach (self::$skip_attributes as $skip_attribute) {
         if (isset($map[$skip_attribute])) {
             unset($map[$skip_attribute]);
         }
         $key = array_search($skip_attribute, $map);
         if ($key !== false) {
             unset($map[$key]);
         }
     }
     return $map;
 }
 public function getMapBetweenObjects()
 {
     return array_merge(parent::getMapBetweenObjects(), self::$map_between_objects);
 }