如何在MVC中进行多字段验证？

public class User
{
    public string Username { get; set; }
    public string Password { get; set; }
    public string ConfirmPassword { get; set; }
    // 其他字段...

    public bool IsValid()
    {
        // 验证规则
        if (string.IsNullOrEmpty(Username))
        {
            ErrorMessage = "用户名不能为空";
            return false;
        }

        if (string.IsNullOrEmpty(Password))
        {
            ErrorMessage = "密码不能为空";
            return false;
        }

        if (Password != ConfirmPassword)
        {
            ErrorMessage = "密码不匹配";
            return false;
        }

        // 其他验证规则...

        return true;
    }
}

<form action="/user/register" method="post">
    <label for="username">用户名：</label>
    <input type="text" id="username" name="username" />

    <label for="password">密码：</label>
    <input type="password" id="password" name="password" />

    <label for="confirmPassword">确认密码：</label>
    <input type="password" id="confirmPassword" name="confirmPassword" />

    <!-- 其他字段... -->

    <input type="submit" value="注册" />
</form>

public class UserController : Controller
{
    [HttpPost]
    public ActionResult Register(User user)
    {
        if (user.IsValid())
        {
            // 验证通过，执行注册逻辑
            // ...

            return RedirectToAction("Success");
        }

        // 验证失败，显示错误消息
        ModelState.AddModelError("", user.ErrorMessage);
        return View();
    }
}