How does Observer("nestjs/event-emitter") differs from CQRS EventBus (nestjs/cqrs) ?

[AlexSun98]

Hi all,

I’d like to express my thanks to the amazing efforts put in this repository.

NestJS provides an event pub/sub at "nestjs/event-emitter" and an event bus at "nestjs/cqrs", I'm a bit of confused about when and where to use "nestjs/event-emitter" and CQRS EventBus (nestjs/cqrs)? Seems others also had same question from this post (nestjs/event-emitter#44), Can anyone shed some light on this please?

Appreciated.

[Sairyss]

Event emitter from nestjs/cqrs as far as I remember does not let you await for all events to finish, it's fire and forget. It means that if something crashes in the middle, event will be lost.
nestjs/event-emitter allows you to await for all events to execute, so we can save everything as a part of a transaction. This way no event is lost, if something fails in the middle entire transaction will be aborted (all or nothing).

For that reason event emitter from nestjs/cqrs is not used and I don't recommend using it.

[AlexSun98]

thanks!