春季如何正确发布DDD域事件？ [英] How to properly publish DDD domain events with spring?

问题描述

我正在尝试在我的项目中实现领域驱动的设计。
这是我的基础 Aggregate 类：

I am trying to implement domain driven design in my project. Here is my base Aggregate class:

public abstract class UUIDAggregate {
    private final DomainEventPublisher domainEventPublisher;

    protected void publish(DomainEvent domainEvent) {
        domainEventPublisher.publish(domainEvent);
    }
}

假设我们有 UserAccount 总计：

public class UserAccount extends UUIDAggregate {
    private String email;
    private String username;
    private String password;
    private String firstName;
    private String lastName;

    public void update() {
        publish(new DomainEventImpl());
    }
}

这是我的 DomainEventPublisher ：

public interface DomainEventPublisher {
   void publish(DomainEvent event);
}

这里是 DomainEventPublisherImpl ：

@Component
public class DomainEventPublisherImpl implements DomainEventPublisher{
    @Autowired
    private ApplicationEventPublisher publisher;

    public void publish(DomainEvent event){
        publisher.publishEvent(event);
    }
}

现在，这似乎是个好主意，域名与实现分开，但这不起作用。 DomainEventPublisher 不能自动连线，因为 UUIDAggregate 不是 @Component 或 @Bean 。一种解决方案是创建 DomainService 并在那里发布事件，但这似乎是域到域服务的泄漏，如果我这样做，我将使用贫血模型。我还能做的是将 DomainEventPublisher 作为参数传递给每个聚合，但这似乎也不是一个好主意。

Now, this seems like a good idea, the domain is separated from implementation but this does not work. DomainEventPublisher cannot be Autowired because UUIDAggregate is not a @Component or @Bean . One solution would be to create DomainService and publish event there but that seems like leaking of domain to domain service and if I go that way, I am going to anemic model. Also what I can do is to pass DomainEventPublisher as a parameter to every aggregate but that also does not seems like a good idea.

推荐答案

一个想法是为域对象建立一个工厂：

One idea would be to have a factory for domain objects:

@Component
class UserAccountFactoryImpl implements UserAccountFactory {
    @Autowired
    private DomainEventPublisher publisher;

    @Override
    public UserAccount newUserAccount(String email, String username, ...) {
        return new UserAccount(email, username, ..., publisher);
    }
}

然后，您创建域对象的代码是 publisher-免费：

Then your code creating a domain object is "publisher-free":

UserAccount userAccount = factory.newUserAccount("[e-mail]", ...);

或者您可以稍微更改事件发布的设计：

Or you might slightly change the design of the event-publishing:

public abstract class UUIDAggregate {
    private final List<DomainEvent> domainEvents = new ArrayList<>();

    protected void publish(DomainEvent domainEvent) {
        domainEvents.add(domainEvent);
    }
    public List<DomainEvent> domainEvents() {
        return Collections.unmodifiableList(domainEvents);
    }
}

@Component
class UserAccountServiceImpl implements UserAccountService {
    @Autowired
    private DomainEventPublisher publisher;

    @Override
    public void updateUserAccount(UserAccount userAccount) {
        userAccount.update();

        userAccount.domainEvents().forEach(publisher::publishEvent);
    }
}

这与您的建议不同：服务发布事件，但不创建，然后-逻辑停留在域对象中。

This is different from your proposal: the service publishes the events, but doesn't create then - the logic stays in the domain object.

此外，您可以更改发布者以最小化样板代码：

Further, you can change your publisher to minimize the boiler-plate code:

public interface DomainEventPublisher {
   void publish(UUIDAggregate aggregate);
}

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