function api_filter_fields(&$filter_data, $required_fields_arr)
 {
     return $filter_data;
     foreach ($filter_data as $key => &$data) {
         if (is_array($data)) {
             foreach ($data as $k => &$v) {
                 //if(!in_array($k, $required_fields_arr)) {
                 //unset($data[$k]);
                 //}
                 if (!isset($required_fields_arr[$k])) {
                     unset($data[$k]);
                 } else {
                     if (is_array($required_fields_arr[$k])) {
                         api_filter_fields($v, $required_fields_arr[$k]);
                     }
                 }
             }
         } else {
             if (!isset($required_fields_arr[$key])) {
                 unset($filter_data[$key]);
             }
         }
     }
 }
 protected static function _get_required_fields(&$filter_arr, $filter_arr_key, $required_fields)
 {
     if (!empty($filter_arr[$filter_arr_key])) {
         api_filter_fields($filter_arr[$filter_arr_key], $required_fields);
     }
 }