private function isRelated()
    {
        $isRelated = false;
        $idSuffix = '_id';
        $pos = strrpos($this->key, $idSuffix);

        if ($pos !== false
            && strlen($this->key) - strlen($idSuffix) === $pos
        ) {
            $isRelated = true;
        }

        return $isRelated;
    }