public function prepare(string $sql, $standalone = false)
    {
        try {
            $stmt = $this->dbh->prepare($sql);
            if ($standalone) {
                return $stmt;
            } else {
                $this->stmt = $stmt;
            }
            return $this;
        } catch (\PDOException $e) {
            die("Error: " . $e->getMessage());
        }
    }