什么是集合函数？ [英] What is an Aggregate Function?

问题描述

我想在业余时间学习事件采购（使用Greg Youngs Event Store）。我已经设置了一个简单的流，可以对其进行读取和写入。

请参见以下链接：

我将在事件存储中拥有哪些事件流？我正在阅读来自一位对此事件非常了解的用户的答复，他建议以下内容：

  AggregateType + AggregateId +版本
  

在此基础上，相信事件的命名如下：

  BookingCreatedEvent511（51是聚合ID，版本1）
 BookingUpdatedEvent511（51是聚合ID，版本1）
 BookingUpdatedEvent512（51是聚合ID，版本2）
 BookingCreatedEvent521（52是聚合ID，版本1）
 BookingUpdatedEvent513（51是聚合ID，版本3） 
 BookingCreatedEvent531（53是聚合ID，1是版本）
 BookingUpdatedEvent514（51是聚合ID，4是版本）
 BookingUpdatedEvent515（51是聚合ID，5是版本） ）
 BookingUpdatedEvent516（51是集合ID，6是版本）
 BookingUpdatedEvent5 17（总ID为51，版本7为版本）
  

因此有10个事件流。这看起来有些混乱，例如，将聚合ID和版本连接在一起-例如，说我有以下内容：

  BookingUpdatedEvent51745 
  

我怎么知道51745的哪个部分是汇总ID，哪个部分是版本。

我正确理解了吗？

解决方案

如果如果是事件搜索域模型，则流等于聚合函数

我找不到任何有意义的证据。

Dan Leech在2014年提交的文档的该部分的原始文本使用了这种拼写方式

如果您是事件采购域模型，则流将等于聚合。

Chris在其中进行的提交更改为可在github 中找到，但是它与主要的重写混在一起，因此没有有关更改的书面说明。

说我有一个订单的汇总（包含订单项），有100万个，那么我将有100万个流，而不是1个。

基本上是。

更确切地说，每个流在逻辑上都与其他所有流都隔离开；事件存储无法为您提供一次对多个流进行原子更改的功能。

因此，域模型中的每个立即一致的事务都应准确地写入一个事件流。

I am trying to learn Event Sourcing (using Greg Youngs Event Store) in my spare time. I have setup a simple stream and I can read from it and write to it.

Please see this link: https://eventstore.org/docs/getting-started/?tabs=tabid-1%2Ctabid-dotnet-client%2Ctabid-dotnet-client-connect%2Ctabid-4. It says:

"If you are Event Sourcing a domain model, a stream equates to an aggregate function."

I don't believe I have ever come across the term Aggregate Function before - I know aggregate root and aggregate, however not aggregate function. Say I have the events below:

BookingCreatedEvent
BookingUpdatedEvent

If I was to create an event log in SQL server then it could look something like this (the Cargo column contains the serialized object):

What Event streams would I have in Event Store for this? I was reading an answer from a user on here who seems to be very knowledgeable about Event Sourcing and he suggested the following:

AggregateType+AggregateId+Version

On that basis believe the events would be named as follows:

BookingCreatedEvent511 (51 is the aggregate ID and 1 is the version)
BookingUpdatedEvent511 (51 is the aggregate ID and 1 is the version)
BookingUpdatedEvent512 (51 is the aggregate ID and 2 is the version)
BookingCreatedEvent521 (52 is the aggregate ID and 1 is the version)
BookingUpdatedEvent513 (51 is the aggregate ID and 3 is the version)
BookingCreatedEvent531 (53 is the aggregate ID and 1 is the version)
BookingUpdatedEvent514 (51 is the aggregate ID and 4 is the version)
BookingUpdatedEvent515 (51 is the aggregate ID and 5 is the version)
BookingUpdatedEvent516 (51 is the aggregate ID and 6 is the version)
BookingUpdatedEvent517 (51 is the aggregate ID and 7 is the version)

Therefore there are 10 event streams. This looks a little confusing i.e. concatenating the aggregate ID and version - for example, say I had the following:

  BookingUpdatedEvent51745

How would I know what part of 51745 is the aggregate ID and what part is the version.

Have I understood this correctly?

解决方案

If you are Event Sourcing a domain model, a stream equates to an aggregate function

I can't find any evidence that means anything.

The original text of that section of the document, committed by Dan Leech in 2014, used this spelling

If you are Event Sourcing a domain model a stream would equate to an aggregate.

The commit where Chris made the change is available in github, but it's mixed in with a major rewrite, so there's no documented explanation for the change.

Say I had an Aggregate of order (containing order items) and there were 1 million of them, then I would have 1 million streams instead of 1

Basically, yes.

More precisely, each stream is logically isolated from all of the others; Event Store doesn't give you facilities to make atomic changes to more than one stream at a time.

So each immediately consistent transaction in your domain model should be writing to exactly one event stream.

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