protected function getCacheTag()
    {
        return md5(serialize([
            __CLASS__,
            $this->db->dsn,
            $this->db->username,
        ]));
    }
protected function getCacheTag()
    {
        return md5(serialize([
            __CLASS__,
            $this->db->dsn,
            $this->db->username,
        ]));
    }
Returns the cache tag name.
This allows [[refresh()]] to invalidate all cached table schemas.
@return string the cache tag name