public function getQuerySet()
 {
     if ($this->_qs === null) {
         $qs = parent::getQuerySet();
         $this->_qs = $qs->filter(array_merge([$this->to => $this->primaryModel->{$this->from}], $this->extra));
         if ($this->primaryModel->getIsNewRecord()) {
             $this->_qs->distinct();
         }
     }
     return $this->_qs;
 }