protected function getCacheKey($method, $fetchMode, $rawSql)
    {
        return [
            __CLASS__,
            $method,
            $fetchMode,
            $this->db->dsn,
            $this->db->username,
            $rawSql,
        ];
    }
protected function getCacheKey($method, $fetchMode, $rawSql)
    {
        return [
            __CLASS__,
            $method,
            $fetchMode,
            $this->db->dsn,
            $this->db->username,
            $rawSql,
        ];
    }
Returns the cache key for the query.

@param string $method method of PDOStatement to be called
@param int $fetchMode the result fetch mode. Please refer to [PHP manual](https://secure.php.net/manual/en/function.PDOStatement-setFetchMode.php)
for valid fetch modes.
@param string $rawSql the raw SQL with parameter values inserted into the corresponding placeholders
@return array the cache key
@since 2.0.16