[doc] Create an example of a Saga for multiple aggregates

[giautm]

Hi. I want to see an example of multiple aggregates in a project to see how they communicate. :)

[maxekman]

Sounds like it could be a good example. Could you describe in more detail what you would like to highlight?

[giautm]

I want to see:

• How two aggregate roots can communicate together.
• How to use two aggregates in a domain service which require two aggregates to complete a command.

[maxekman]

Basically you should never have a command that directly affects multiple aggregate roots. If you need that you should probably create a saga that issues one of the commands as a side effect to an event from the first command.

Relating to your question, a more complex saga example could be good to have. I'll try to add that at some point.

[giautm]

Tks, I will waiting for the example. May I contribute to that PR for learning?

[maxekman]

You can propose an example if you want to learn about it.

Maybe a e-commerce checkout could be a good example:

• One simple domain called Order, with commands and events for Create, Fulfil and Reject.
• One simple domain called Payment, with a command Request with events Accepted and Denied.
• A saga that reacts on Order.Created and issues a Payment.Request command. It will then fulfil or reject the order depending on if the payment was accepted or denied.

[chaudharisuresh997]

Idea is too have small aggregate. One aggregate does not have other aggregate instead it can have id of aggrgate. If u read akka actor model it says result of one aggrgate can be passed to other. Here one aggrgate result can be passed to other.

[screwyprof]

Shouldn't a saga be able to react on a bunch of events? Currently It's interface only relies on a single event only.

[maxekman]

In that case the saga has to keep track of incoming events until it has collected all affected events. Then it can continue processing. A saga is meant to keep its own internal state if required.