这里是一个简单的例子,我正在运行的问题不在于这里提供的一些想法和其他关于DDD的地方.
说我有一个ASP.NET MVC 3网站创建/操纵一个人.控制器访问应用程序服务层(PersonService),后者又使用域实体(EF 4 POCO)和PersonRepository进行更改并持久化.为了简单起见,我在这里省略了所有的界面.在这种情况下,人是根,为了简单起见,只有电子邮件地址(也假定电子邮件不是不可变的,可以更新).
选项1：
尝试坚持使用DDD的基础知识,其中与实体直接相关的行为实现为实体的一部分(Person实现AddEmail,ChangeEmail等).唯一的问题是,除了Add *方法之外,Person将需要知道上下文或实体框架(将删除任何持久性无知)或需要使用“服务”或存储库来标记电子邮件已修改.
// Person Service
public class PersonService {
// constructor injection to get unit of work and person repository...
// ...methods to add/update a person
public EmailAddress AddEmailAddress(int personId,EmailAddress email)
{
Person p = personRepository.Find(p => p.Id == personId).First();
p.AddEmail(email);
uow.SaveChanges();
return email;
}
public EmailAddress ChangeEmailAddress(EmailAddress email)
{
Person p = personRepository.Find(p => p.Id == personId).First();
p.ChangeEmail(email);
// change state of email object here so it's updated in the next line???
// if not here,wouldn't the Person entity have to know about the context
// or use a service?
uow.SaveChanges();
return email;
}
}
// Person Repository
public class PersonRepository
{
// generic repository implementation
}
// Person Entity
public class Person
{
public string Name { get;set; }
public IEnumerable<EmailAddress> EmailAddresses { get;set; }
public void AddEmail(EmailAddress email)
{
this.EmailAddresses.Add(email);
}
public void ChangeEmail(EmailAddress email)
{
EmailAddress orig = this.EmailAddresses.First(e => e.Id == email.id);
// update properties on orig
// NOW WHAT? [this] knows nothing about the context in order to change state,etc,or do anything to mark the email add updated
}
}
// Email
public class EmailAddress
{
public string Email { get;set; }
public bool IsPrimary { get;set; }
}
选项二：
让个人服务使用存储库来添加/更新电子邮件地址,并且不对该实体执行行为.在许多关系(例如地址,两个表需要更新以完成工作)的情况下,这种情况要简单得多,但是模型就变成了一大堆的getter和setter.
// Person Service
public class PersonService {
// constructor injection to get unit of work and person repository...
// ...methods to add/update a person
public EmailAddress AddEmailAddress(int personId,EmailAddress email)
{
Person p = personRepository.Find(p => p.Id == personId).First();
personRepository.AddEmail(personId,email);
uow.SaveChanges();
return email;
}
public EmailAddress ChangeEmailAddress(EmailAddress email)
{
personRepository.ChangeEmail(email);
uow.SaveChanges();
return email;
}
}
// Person Repository
public class PersonRepository
{
// generic repository implementation
}
// Person Entity
public class Person
{
public string Name { get;set; }
public IEnumerable<EmailAddress> EmailAddresses { get;set; }
}
// Email
public class EmailAddress
{
public string Email { get;set; }
public bool IsPrimary { get;set; }
}
无论如何,有什么想法吗？
谢谢Brian
选项1是要走的路.
推理是简单的 – 更改电子邮件地址是领域关注.我敢打赌你的域名专家说他们将需要更改电子邮件.自动将电子邮件更改的逻辑标记为应该在域模型中生活的业务逻辑.对象主要由他们的行为定义,而不是他们所持有的数据.
另外 – 在您选择使用工作单位之前,先考虑一下,并将所有服务都包装起来.总结根应该是绘制事务边界,如果服务器只包含存储库和域对象调用,服务通常是无用的.
我会有这样的事情：
public class Person{
public Email Email{get;private set;}
public void SpecifyEmail(Email email){
//some validation,if necessary
EnsureEmailCanBeChanged();
//applying state changes
Email=email;
//raising event,if necessary
Raise(new EmailChanged(this));
}
public class EmailChanged:Event<Person>{
public EmailChanged(Person p):base(p){}
}
}
public class Email{
public Email(string email){
//validations (e.g. email format)
Value=email;
}
//implicit to string,explicit from string conversions
}
public class PersonController{
public ActionResult SpecifyEmail(int person,string email){
_persons.Get(person).SpecifyEmail((Email)email);
return RedirectToAction("Person",new{person});
}
}
我正在使用NHibernate – 它足够聪明,以确定自从上次持续存在以来发生了什么变化.很难说实体框架如何处理这个.
