When a service calls another service

[JuTiger-Lee]

Hi
For example When UserService need FeedService getFeed method
How to import FeedService?
Should a service use a port when fetching another service? Or should I use commandBus?

[Sairyss]

Depends on your preference. You can use a port, or you can put feed retrieving logic into a query and use a queryBus, this will make things more decoupled.
Don't use a commandBus to fetch things, there is a queryBus for this. Command bus exists only for mutations.

[Sairyss]

So is that correct

Yes

if I import FeedQuery in the context of User, would there be any issues?

FeedQuery is just a DTO so it's fine to import.
You should think about your modules in this way: if you take a module and move it into a separate microservice, will it work with minimal changes? If it uses a query bus, you can just change it to use a RPC call, copy-paste the DTO and it should work, no other changes required. If you use a service, this will require bigger refactoring.

[vyvian1712]

Your information is very helpful to me, thank you!

[vyvian1712]

When executing a FeedQuery within UserService like this, do I need to include FeedQueryHandler (located in /modules/feed/queries/feed.query-handler.ts) in the providers array of user.module.ts, right?

Does this create any dependencies?

[Sairyss]

When executing a FeedQuery within UserService like this, do I need to include FeedQueryHandler (located in /modules/feed/queries/feed.query-handler.ts) in the providers array of user.module.ts, right?

FeedQueryHandler goes to providers of a Feed module, not User module.

[vyvian1712]

Sorry, I got a little confused with NestJS