public function create(string $user_name, string $real_name, string $email, string $password): User
    {
        DB::table('user')->insert([
            'user_name' => $user_name,
            'real_name' => $real_name,
            'email'     => $email,
            'password'  => password_hash($password, PASSWORD_DEFAULT),
        ]);

        $user_id = (int) DB::connection()->getPdo()->lastInsertId();

        return new User($user_id, $user_name, $real_name, $email);
    }