如何开始DDD(续)

上一篇针对用户注册案例简单介绍了如何使用 DDD，接下来我将继续针对这个例子做一下补充。先将User模型丰富起来，因为目前看上去他和贫血模型还没有啥大的区别。

首先还是由领域专家来说明业务，他提出了用户注册成功后需要完善个人信息，这些信息包括姓名、生日、手机号。还需要用户提供一些联系信息，如地址，邮编等。那么我们就可以根据业务定义方法了。昨天netfocus兄指正了loginid所产生的歧义，表示认同，所以今天一并修改了一下。

public class AddressInfo
{
    public AddressInfo(string province, string city, string address, string postcode)
    {
        this.Province = province;
        this.City = city;
        this.Address = address;
        this.Postcode = postcode;
    }

    public string Province { get; private set; }
    public string City { get; private set; }
    public string Address { get; private set; }
    public string Postcode { get; private set; }
}

public class User
{
    public User(string name, string password, string email)
    {
        this.Name = name;
        this.Password = password;
        this.Email = email;
    }

    public string Id { get; private set; }
    public string Name { get; private set; }
    public string Password { get; private set; }
    public string RealName { get; private set; }
    public string Email { get; private set; }
    public string Cellphone { get; private set; }
    public string Birthday { get; private set; }
    public AddressInfo Address { get; private set; }

    public void UpdateBasicInfo(string realName, string birthday, string cellphone)
    {
        this.RealName = realName;
        this.Birthday = birthday;
        this.Cellphone = cellphone;
    }

    public void UpdateAddress(AddressInfo address)
    {
        this.Address = address;
    }
}

那么前端的代码也很简单

public class UserController
{
    private readonly IUserRepository _userRepository;
    public void SetProfile(FormCollection form)
    {
        var user = _userRepository.Get(form.Get("id"));

        user.UpdateBasicInfo(form.Get("name"), form.Get("birthday"), form.Get("cellphone"));
    }

    public void SetAddress(FormCollection form)
    {
        var user = _userRepository.Get(form.Get("id"));

        var address = new AddressInfo(form.Get("province"), form.Get("city"), 
            form.Get("address"), form.Get("postcode"));

        user.UpdateAddress(address);
    }
}

以上的代码很好理解，只是设计了一个AddressInfo的值对象。

接下来将演示一下用户登录验证和修改密码。一般的做法：

public interface IUserRepository
{
    User GetByName(string loginId);
}

public class UserController
{
    private readonly IUserRepository _userRepository;
    public UserController(IUserRepository userRepository)
    {
        this._userRepository = userRepository;
    }

    public void Logon(FormCollection form)
    {
        User user = _userRepository.GetByName(form.Get("LoginId"));
        if (user == null)
            throw new Exception("loginId", "账号不存在。");
        if (user.Password != form.Get("Password"))
            throw new Exception("password", "密码不正确。");

        FormsAuthentication.SetAuthCookie(user.Name, createPersistentCookie);
    }
}

请注意上述代码比较密码是错误的方式，因为上一篇说明了密码是加过密的。所以要修改一下，首先要注入IEncryptionService，那么就会这样判断

if (user.Password != _encryptionService.Encrypt(form.Get("Password")))

这样会有什么问题呢。目前IEncryptionService的接口相对还比较简单，如果IEncryptionService提供了针对不同业务的好多加密接口，那么前端人员就需要详细了解IEncryptionService的api，增加了复杂度。再对User封装一个方法，然后对Contoller代码再稍做修改

public class User
{
    public bool VerifyPassword(string password, IEncryptionService encryptionService)
    {
        return this.Pasword == encryptionService.Encrypt(password);
    }
}

public class UserController
{
    public void Logon(FormCollection form)
    {
        User user = _userRepository.GetByName(form.Get("LoginId"));
        if (user == null)
            throw new Exception("loginId", "账号不存在。");
        if (user.VerifyPassword(form.Get("Password"), _encryptionService))
            throw new Exception("password", "密码不正确。");

        FormsAuthentication.SetAuthCookie(user.Name, createPersistentCookie);
    }
}

这样具体密码采用了什么加密接口就不用关心了，将此规则封闭在了domain内，还有一个主要目的是为了修改密码时能够复用。也许你并不认同这种做法，好像也没啥变化，当然也没关系，解决问题就行，我只想表达聚合可以封装哪些方法。
再仔细考虑我觉得上述代码表达的业务还是比较多，首先要查询该登录名的用户是否存在，再去验证密码，如果需求再有其他规则，如禁用的用户不能登录，具有时效性的用户过期了也不能登录等等，这样是不是越来越复杂，前端开发人员需要掌握的业务知识就会越来越多，所以最好将此业务封装在领域内，ui端只需要传入登录名和密码。
说了这么多，User本身是无法做到这一点的，那么还是要将这些业务规则写在上一篇提到过的DomainService

public class DomainService
{
    private readonly IUserRepository _userRepository;
    private readonly IEncryptionService _encryptionService;
    public DomainService(IUserRepository userRepository, IEncryptionService encryptionService)
    {
        this._userRepository = userRepository;
        this._encryptionService = encryptionService;
    }

    public User Authenticate(string loginId, string password)
    {
        var user = _userRepository.GetByName(loginId);
        if (user == null)
            throw new Exception("loginId", "账号不存在。");
        if (!user.VerifyPassword(password, _encryptionService))
            throw new Exception("password", "密码不正确。");

        return user;
    }
}

public class UserController
{
    public void Logon(FormCollection form)
    {
        try {
            User user = _domainService.Authenticate(form.Get("LoginId"), form.Get("Password"));
            FormsAuthentication.SetAuthCookie(user.Name, createPersistentCookie);
        }
        catch (Exception) {
            throw;
        }
    }
}

这样是不是更好一点呢？
接下来再来说修改密码。直接上代码吧

public class User
{
    public void ChangePassword(string oldPwd, string newPwd, IEncryptionService encryptionService)
    {
        if (!this.VerifyPassword(oldPwd, encryptionService))
            throw new Exception("旧密码输入不正确。");

        this.Pasword = encryptionService.Encrypt(newPwd);
    }
}

public class UserController
{
    public void ModifyPassword(FormCollection form)
    {
        try {
            User user = _userRepository.GetByName(User.Identity.Name);
            user.ChangePassword(form.Get("oldPwd"), form.Get("newPwd"), _encryptionService);
            _userRepository.Update(user);
        }
        catch (Exception) {
            
            throw;
        }
    }
}

好吧，这到这里吧，希望对你有帮助。下一篇再继续讨论丰富一下用户注册的过程，引入事件驱动。