How to use multiple subscriptions and unsubscribes?

[pantonis]

Hi,

Using one instance of a StompService can I subscribe to multiple queues?

[kum-deepak]

Yes, you can subscribe any number of queues. Just make multiple calls to subscribe.

Please check the samples as well. If you are new to dependency injection, please add the StompService to provide list in app.module.ts (as suggested in samples). That way same instance of the STOMP connection will be used across your application.

[pantonis]

And each subscription must be assigned to a different observable?

[kum-deepak]

When you make a call to subscribe, a new Observable is returned, which will provide messages for that queue.

[pantonis]

Forgive me I am not web dev expert.

 this.messages = this._stompService.subscribe('/topic/ng-demo-sub');
 this.messages2 = this._stompService.subscribe('/topic/ng-demo-sub2');

or

 this.messages = this._stompService.subscribe('/topic/ng-demo-sub');
 this.messages = this._stompService.subscribe('/topic/ng-demo-sub2');

[kum-deepak]

The first one:

this.messages = this._stompService.subscribe('/topic/ng-demo-sub');
this.messages2 = this._stompService.subscribe('/topic/ng-demo-sub2');

[pantonis]

and to unsubscribe

this.subscription.unsubscribe();

is this enough for both subscriptions?

[kum-deepak]

No, the code will look something like following (I haven't executed the code, just typed here):

// use messages from /topic/ng-demo-sub by subscribing to the Observable
this.messages = this._stompService
  .subscribe('/topic/ng-demo-sub')
  .subscribe((msg: Message) => {
    // use it
  });

// use messages from /topic/ng-demo-sub2 by subscribing to the Observable
this.messages2 = this._stompService
  .subscribe('/topic/ng-demo-sub2')
  .subscribe((msg: Message) => {
    // use it
  });

// Unsubscribe from /topic/ng-demo-sub
this.messages.unsubscribe();
this.messages = null;

// Unsubscribe from /topic/ng-demo-sub2
this.messages2.unsubscribe();
this.messages2 = null;

The above has been updated.

[kum-deepak]

In summary both the subscriptions are independent of each other and do not affect each other.

[pantonis]

ok thanks a lot

[marcelormourao]

this.messages = this._stompService.subscribe('/topic/ng-demo-sub');
this.messages2 = this._stompService.subscribe('/topic/ng-demo-sub2');

// use messages from /topic/ng-demo-sub by subscribing to the Observable
this.messages.subscribe((msg: Message) => {
   // use it
});

// use messages from /topic/ng-demo-sub2 by subscribing to the Observable
this.messages2.subscribe((msg: Message) => {
   // use it
});

// Unsubscribe from /topic/ng-demo-sub
this.messages.unsubscribe();
this.messages = null;

// Unsubscribe from /topic/ng-demo-sub2
this.messages2.unsubscribe();
this.messages2 = null;

I am using StompRService and when I call this.messages2.unsubscribe() the queueName in the unsubscribe function is '/topic/ng-demo-sub'.

[kum-deepak]

@marcelormourao, please create a demo project demonstrating the issue. You can fork one of the demo projects (links in the README). Thanks!

Meanwhile I am also taking a look.