Event Handler / Saga / Where to Write Documentation about cqrs

[subovietnam]

how using to rollback transaction in cqrs and event sourcing, in sagas when have event failed or message broker failed. Thanks all

[jsonberry]

Your pattern sounds logical, for this case either an event handler or a Saga could work... I would go with a Saga, because you know the next step in the flow is a command (create account), and Sagas always end in a command being issued. Sagas are my goto as a way to orchestrate events with commands. Their most powerful feature IMHO is the async behavior via RxJS, when I needed to fire off commands and then wait for success/failure events inside the same saga to continue processing...(that’s how I handle rollback type features). I have ended up using Event Handlers often, and I usually designated them to encapsulate logic where a write to an aggregate or the storage of event wasn’t going to happen... basically like side effects... logging, email/sms notifications, sending events to other systems event pipelines like an AWS SQS queue. They’re great for that stuff.

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On Tue, Jan 12, 2021 at 9:08 PM Kodeine ***@***.***> wrote: @jsonberry <https://github.com/jsonberry> i'm in the same boat as you were a while ago, could you please confirm if i'm following the right pattern. Account has many users. User App: CreateUserCommand -> write to db, result goes to aggregate -> commit() -> UserCreatedEvent Account App: Saga ofType UserCreatedEvent -> use the userId from event send new command -> CreateAccountCommand i'm not using UserCreatedEventHandler here... should i be doing writes in there? so what needs to happen in command handler then... — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#64 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAXQSKBC2JQEM5DKZUML52LSZUTEFANCNFSM4HD7I52A> .

[jsonberry]

As I've continued on in my ES/CQRS learning I've become more familiar with the patterns so where to do a write is not so elusive now.

It looks like people want to expand the official NestJS CQRS example, so maybe I can make some suggestions on that project while I'm continuing to learn.

Cheers 🍻

[kodeine]

@jsonberry i'm in the same boat as you were a while ago, could you please confirm if i'm following the right pattern.

Account has many users.

User App: CreateUserCommand -> write to db, result goes to aggregate -> commit() -> UserCreatedEvent

Account App: Saga ofType UserCreatedEvent -> use the userId from event send new command -> CreateAccountCommand

i'm not using UserCreatedEventHandler here... should i be doing writes in there? so what needs to happen in command handler then...