在域模型对象中使用工厂？
场景：
在我的应用程序（使用丰富的域模型，其中逻辑位于模型中，而不是在服务中）中，我有用户。我使用服务创建新用户
User newUser = userService.createNewUser("Hans Dampf");
或从数据库获取它们
User oldUser = userDao.findByName("Hans Dampf");
因为在每次调用我的应用程序时我都可以直接访问用户对象，所以我想使用用户对象作为我的域模型的入口点。
每个用户可以有不同类型的画廊，保存在另一个表中。
class User {
@OneToMany(fetch = FetchType.LAZY)
@JoinColumn(name = "userId")
private Set<Gallery> automatic = new HashSet<Gallery>();
}
我想要一种简单的方法来启用特定的画廊。所以我的 API 看起来像：
User user = ... // creating or retriving user
user.enableMainGallery();
在这个方法中，有必要创建一个新的画廊对象并将其添加到画廊列表中。但是如何创建这个新实例呢？使用工厂？这需要将工厂注入域对象（可能有问题）。
public void enableAutomaticGallery() {
automatic.add(automaticFactory.createAutomaticGallery(this));
}
或者我的接口定义有缺陷？我应该以其他方式定义它，这样我就不必注入工厂吗？如何？
Scenario:
In my application (which utilises an rich domain model, where the logic is in the model, not in the services) I have users. I create new users with a service
User newUser = userService.createNewUser("Hans Dampf");
or get them from the database
User oldUser = userDao.findByName("Hans Dampf");
Because in every call into my application I have direct access to an user object, I would like to use the user object as an entry point into my domain model.
Each user can have different types of Galleries, saved in an other table.
class User {
@OneToMany(fetch = FetchType.LAZY)
@JoinColumn(name = "userId")
private Set<Gallery> automatic = new HashSet<Gallery>();
}
I want to have a simple way to enable a specific gallery. So my API would look like:
User user = ... // creating or retriving user
user.enableMainGallery();
Inside this method it would be necassary to create a new gallery object and add it to the list of galleries. But how to create this new instance? Using a factory? That would require to inject the factory into the domain object (may be problematic).
public void enableAutomaticGallery() {
automatic.add(automaticFactory.createAutomaticGallery(this));
}
Or is my interface definition flawed? Should I define it in some other way, such that I don't have to inject the factory? How?
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评论（2）
正如您所说，域对象不应该依赖于应用程序级对象，例如工厂或 Daos。
该域通常是：
因此您的
enableAutomaticGallery方法应该位于 Service 对象上。它可以具有相同的代码，但取决于应用程序。
As you say, the domain objects should not be made dependent on application-level objects such as factories or Daos.
The domain is typically :
So your
enableAutomaticGallerymethod should be on a Service object.It can have the same code, but will be application-dependent.
您的域模型应该对任何服务或 DAO 层甚至任何工厂对象一无所知。
我建议您不要使用需要将 Gallery 对象添加到实例集合的方法 User.enableMainGallery() ，而是公开一个方法
User.addGallery（图库）。这样，负责“启用图库”的类通过将对象添加到
list集合中来实现此目的。换句话说，我不认为
User对象应该负责了解“启用主图库”的含义。这听起来像是属于业务逻辑范畴的东西（我知道这是一个含糊的术语）。Your domain model should know nothing about any service or DAO layers or even any factory objects.
I would suggest instead of a method
User.enableMainGallery()which needs to addGalleryobjects to the instance collection (as you've said), that you instead expose a methodUser.addGallery(Gallery).This way, the classes responsible for "enabling the gallery" do so by adding objects to the
listcollection.In other words, I don't believe that the
Userobject should be responsible for knowing what it means to "enable a main gallery". This sounds like something that falls under the umbrealla of business logic (ambiguous term, I know).