CODEWITHSUNDEEP
angularrxjs
alphapilgrim
alphapilgrim

Reputation: 3975

Angular 7/ RxJs : Poll endpoint with response of first endpoint

I have an endpoint(initiate$) that I hit and it returns a queueId, with that queueId I hit another endpoint until that endpoint returns the status of ready. I have some code that works but it calls both endpoints continuously. I know why it calls both but I can't figure out how to best separate the call to just hit the second endpoint(status$) one on subsequent calls.

RxJs: "^6.3.3" 

downloadTransactionList() {
  const initiate$ = this.exampleService.startListExport(userId, filter);
  const status$ = this.exampleService.pollListExport(initiate$);
  const polling$ = timer(0, 10000).pipe(
    mergeMap(() => status$),
    takeWhile(resp => resp.status !== 'ready')
  );
  initiate$.pipe(mergeMap(() => polling$)).subscribe(r => console.log(r));
}

Upvotes: 1

Views: 215

Answers (3)

JeanPaul A.
JeanPaul A.

Reputation: 3724

If I have understood you correctly, you want that initially, a call to get a queue id is done once, and afterwords, a poller is initiated to poll for data, until the returned status is ready correct?

Try the following

downloadTransactionList() {
   // This calls startListExport to get the queue id
   this.exampleService.startListExport(userId, filter).subscribe((queueId:string) => {
       // When it has successfully returned, initiate the poller
       let timerSubscription:Subscription = timer(0, 10000).pipe(switchMap(() => {
           // Assuming this returns an observable with the status
           return this.exampleService.pollListExport(queueId);
       })).subscribe((data:myType) => {
           // DO something with your data

           // Unsubscribe to stop the poller when criteria is met
           if (data.status === 'ready') {
              timerSubscription.unsubscribe();
           }
       })
   });
}

Upvotes: 0

Julius Dzidzevičius
Julius Dzidzevičius

Reputation: 11000

Use a shareReplay() operator. It multicasts source observable via ReplaySubject (in other words - ReplaySubject subscribes to the source and broadcasts it's last value to future observers).

this.exampleService.startListExport(userId, filter).pipe(shareReplay())

For the reference, here is a DEMO

Upvotes: 1

Adrian Brand
Adrian Brand

Reputation: 21628

Use switchMap instead of mergeMap

Upvotes: 0

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