聚合可以使用聚合查找服务还是业务逻辑应该在域服务中？

Question

我正在使用带有事件源的 CQRS 开发 DDD 软件。现在我想弄清楚我应该把我的业务逻辑放在哪里。

我有一个引用 triggerId（触发器聚合根）的条件聚合根。我还有一个 conditionGroup 聚合根，其中包含一个 conditionId 列表。我有一个看门狗聚合根，它包含一个 conditionGroupId。

当调用触发器聚合的Create 方法时，域发出一个triggerReceived 事件。 triggerReceived 事件具有 triggerId 和一个值属性，应由链接到条件聚合中的 triggerId 的条件进行检查。

我在域端有一个订阅者监听这个事件。我的计划是检索订阅者中的所有看门狗并调用方法 watchdog.ShouldBark(triggerId, value)。看门狗然后需要查找 ConditionGroup 聚合（它的 ConditionGroupId 为属性）并调用 ConditionGroup.DoesGroupMatch(triggerId, value)。 ConditionGroup 必须查找所有 Condition 聚合（它有一个 conditionId 列表）并调用 Condition.DoesConditionMatch(triggerId, value) 方法。

因此每个聚合都必须查找其他聚合以访问一个业务逻辑方法，该方法进行一些检查（未完成更新）。

或者在域中有一些 watchdogService 并且 watchdog 服务执行所有聚合查找并具有业务逻辑是否更好？

所以我的问题是：聚合是否可以通过使用接口 (IAggregateStore) 进行业务逻辑检查来查找其他聚合（没有更新，因为每个事件只应更新一个聚合）？

Answer 1

您的描述相当不完整，因此这个答案也可能不完整。根据您的描述 -

I have a subscriber on the domain side which listens to this event. My plan is to retrieve all watchdogs in the subscriber and call a method watchdog.ShouldBark(triggerId, value).

我在你的域设计中闻到了一些非常糟糕的东西。 ShouldBark 方法的目的是什么。它必须更改您的 WatchDog 域的状态。如果是这样的话，你走错了方向。

让我们先获取您的业务领域。 触发器,条件,条件组,看门狗.

I have a condition aggregate root which references a triggerId (trigger aggregate root).

所以，你在触发器聚合中的代码应该是这样的（你可能已经发现我的一些代码是伪代码）-

public class Trigger : AggregateRoot
{
    ...
    public void CreateTrigger(int value)
    {
        //You can also pass new guid for trigger from your service
        Guid triggerId = Guid.NewGuid();
        var @event = new TriggerReceived(triggerId, value);
        PublishEvent(@event);
    }
}

//this is your event
public class TriggerReceived
{
    public readonly int Value;
    public readonly Guid TriggerId;
    public TriggerReceived(Guid triggerId, int value)
    {
        Value = value;
        TriggerId = triggerId;
    }
}

现在进入正确的方向。不要检索所有 watchDog，而是订阅您的 Condition 服务到此事件。

public class ConditionService
{
    public void When(TriggerReceived @event)
    {
        //re-hydrate your condition aggregate root from event store
        var condition = getConditionByTriggerId(@event.TriggerId);
        //if you want to retrieve condition based on Value you can do that here
        //var condition = getConditionByValue(@event.Value);
        if(condition is not null)
            condition.MatchTrigger();
    }
}

然后在你的条件下聚合 -

public class Condition : AggregateRoot
{
    ...
    public void MatchTrigger()
    {
        //your business logic here
        ...
        //we know trigger value matched one condition, so raise the next event
        publish(new TriggerConditionMatched(this));
    }
}

//this is your TriggerConditionMatched event
public class TriggerConditionMatched
{
    public readonly Condition Condition;
    public TriggerConditionMatched(Condition condition)
    {
        Condition = condition;
    }
}

基于此 -

I also have a conditionGroup aggregate root which holds a list of conditionIds.

我们还可以声明，每个条件都应该有一个名为 ConditionGroupId 的属性。订阅您的 ConditionGroup 服务以收听上述事件 -

public class ConditionGroupService
{
    public void When(TriggerConditionMatched @event)
    {
        //re-hydrate your condition group aggregate root from event store
        var conditionGroup = getConditionGroup(@event.Condition.GroupId);

        if(conditionGroup is not null)
            conditionGroup.MatchTriggerToConditionGroup();
    }
}


public class ConditionGroup : AggregateRoot
{
    ...
    public void MatchTriggerToConditionGroup()
    {
        ...
        //do some check here, your business logic

        //raise the next event
        publish(new TriggerConditionGroupMatched(this));
    }
}

//this is your TriggerConditionGroupMatched event
public class TriggerConditionGroupMatched
{
    public readonly ConditionGroup ConditionGroup;
    public TriggerConditionGroupMatched(ConditionGroup conditionGroup)
    {
        ConditionGroup = conditionGroup;
    }
}

最后，基于此——

And I have a watchdog aggregate root which holds a conditionGroupId.

您的 ConditionGroup 域中应该有一个 watchDogId 属性。所以，订阅你的 WatchDog 服务来监听 TriggerConditionGroupMatched 事件 -

public class WatchDogService
{
    public void When(TriggerConditionGroupMatched @event)
    {
        //re-hydrate your Watch Dog aggregate root from event store
        var watchDog = getWatchDog(@event.ConditionGroup.WatchDogId);

        if(watchDog is not null)
            watchDog.Bark();
    }
}

public class WatchDog : AggregateRoot
{
    ...
    public void Bark()
    {
        ...
        this.ShouldBark = true;

        //you should raise your next event
        publish(nextEvent);
    }
}

您可能已经发现这是一个事件和订阅者的网络，但请记住，事件源系统应该始终是最终一致的。通过这种方式，您可以记录 Trigger 或 Condition 或 ConditionGroup 或 看门狗.

聚合可以使用聚合查找服务还是业务逻辑应该在域服务中？

May an aggregate use an aggregate lookup service or should the business logik be in a domain service?

c#

domain-driven-design

cqrs

event-sourcing