在 CQRS 中，如何将聚合上允许的方法列表传达给 UI？
我有一个聚合根“订单”，它有许多方法在内部设置其“状态”字段：
- 提交
- 、暂停、
- 起飞、
- 确认、
- 取消
- 等。
可用的操作取决于订单的当前状态（例如，如果已经处于搁置状态，则不能将其搁置）。问题是我需要提供一个查询来告诉 UI 哪些命令可用，以便我可以隐藏否则会引发 InvalidOperationException 的操作。
如何在最小化 DRY 违规的情况下做到这一点？
I have an aggregate root 'Order', and it has a number of methods on it which internally set its 'Status' field:
- Submit
- Place On Hold
- Take Off Hold
- Confirm
- Cancel
- etc.
The available actions are dependent upon the current Status of the order (e.g. it can't be put on hold if it's already on hold). The problem is that I need to provide a query to tell the UI which commands are are available so I can hide the operations that would otherwise throw an InvalidOperationException.
How do I do this with minimal DRY violation?
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最简单的解决方案是投影当前状态以及可用于读取/查询模型的转换，并选择它以及要显示的数据。
例子：
PlaceOnHoldCommand会产生OrderPlacedOnHoldEvent，该事件（除了放入 EventStore 中）由OrderTransitionsEventHandler发布和处理，从而对可用转换进行非规范化到与订单关联的数据库表。客户端选择可用的转换并进行相应的操作（隐藏不可用的按钮或类似的东西）。这当然是选项之一。但不要指望不会有任何重复。 CQRS 有助于管理复杂性，有时这意味着会发生轻微的 DRY 违规。
The simplest solution is to project current status along with available transitions to read/query model and select it along with the data to display.
Example:
PlaceOnHoldCommandresults inOrderPlacedOnHoldEventwhich (besides being put in EventStore) is published and handled byOrderTransitionsEventHandlerwhich denormalizes available transitions to a DB table associated with Order. The client selects available transitions and acts accordingly (hides unavailable buttons or sth. like that).This is of course one of options. Don't expect however that there will be no duplication whatsoever. CQRS helps to manage complexity and sometimes this means slight violations of DRY occur.