public function getRelatedForeignKey()
    {
        if (is_null($this->_relatedForeignKey)) {
            $tblName = Entity\Manager::getInstance()
                ->get($this->_relatedEntity)
                ->getEntity()->getTableName();
            $name = Text::singular($tblName);
            $this->setRelatedForeignKey("{$name}_id");
        }
        return $this->_relatedForeignKey;
    }