您如何处理CQRS中的外键读取侧故障？ [英] How do you handle foreign-keys read-side failures in CQRS?
问题描述
SQL数据模型中有表A和表B，表A具有指向表B的外键。现在，您要将CRUD体系结构迁移到CQRS。想象以下情况：
You have table A and table B in your SQL data model, with table A having a foreign key towards table B. You now want to migrate your CRUD architecture to CQRS. Imagine the following scenario:
- 您收到一条命令以保留A的新条目
- 您写入您的附加日志并对其进行处理，以更新您的状态
- 读取端将其拾取并未能插入数据库中
在这种情况下，您的写端和读端将永远无法达到一致性。您如何处理CQRS中的读取侧约束？
In this situation, your write side and read side will never reach consistency. How do you handle read-side constraints in CQRS? Should validation occurs in the write side instead?
推荐答案
我相信您可以从中得到一些启发：
I believe you can get some inspiration from this:
它的简称是，新的A聚合需要由另一个聚合创建，比如C（创建者）。在这种情况下，C保留了所有A的ID的列表，因此可以在聚合级别而不是视图模型上进行检查。
The short of it is, the new A aggregate needs to be created by another aggregate, let's say C (creator). In this case C holds a list of all A's IDs, so that the check can be done at the aggregate level instead of the view model.
如果您的问题更为笼统然后问如何处理视图模型更新失败，这实际上取决于。可能是设计问题（例如错误的事件顺序，缺少先决条件或不变的检查），错误或其他。我通常要做的是，如果没有自动补救措施，我将这些实体锁定并发送到需要手动干预的实体列表中。
If your question is more generic and you ask "how do you handle view model update failures", then it really depends. It could be a design issue (e.g. incorrect sequence of events, lack of pre-conditions or invariant checks), a bug, or else. What I normally do is that I lock those entities and send them to a list of entities requiring manual intervention, if there is no automatic remedial.
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