code: public function isRelatedKey($key)
      {
          if (!$this->parser->isRelatedKey($key)) {
              return false;
          }
  
          list($join, $key) = $this->toJoinAndKey($key);
  
          return $this->model->getTable() != $join;
  
      }
docs: {@inheritdoc}
  
  @param string $key The key name
  @return bool