public function setMode(int $mode = PGSQL_ASSOC): self
    {
        if (PGSQL_ASSOC !== $mode && PGSQL_NUM !== $mode) {
            throw new exceptions\InvalidArgumentException(
                __METHOD__ . ' accepts either of PGSQL_ASSOC or PGSQL_NUM constants'
            );
        }
        $this->mode = $mode;

        return $this;
    }