code: public function beforeDelete()
      {
          // store tag ids list
          $this->_tagsForDelete = [];
          $relation = $this->owner->getRelation('tagsList', false);
          if ($relation instanceof ActiveQuery) {
              $this->_tagsForDelete = (new Query())
                  ->select(current($relation->link))
                  ->from($relation->via->from[0])
                  ->where([key($relation->via->link) => $this->owner->getPrimaryKey()])
                  ->column($this->owner->getDb());
          }
      }
docs: Before delete event