Observable of array to array (Rxjs)

Question

I have a service and its getAllMessages() returns an observable of an array of items : Observable<ITEM[]>

I map the result like this to post each ITEM to a RestAPI :

this.service.getAllMessages()
.map(items => ...for each item of items, call this.apiService.postMessage(item)...)

postMessage(item) returns an Observable<Response>

My goal is to get an Observable<Response[]> for which I can check the http code of every post from this.apiService.postMessage(item)

I tried using flatMap :

this.service.getAllMessages()
  .flatMap(items => {
    return items.map(item => {
      return this.apiService.postMessage(item);
    });
  }).subscribe(RES => {
    console.log(RES);
  });

but here RES is an Observable<Response> and not a simple Response

How can I achieve this ?

CozyAzure · Accepted Answer · 2017-10-19 17:17:47Z

2

What is returned by your this.service.getAllMessages() is an array of Observable, not an Observable of array. The .map() function belongs to the function of array.

If you want to execute all the Observables in parallel, use .forkJoin():

this.service.getAllMessages()
    .flatMap(items => {
        return Observable.forkJoin(items.map(item => this.apiService.postMessage(item)));
    })
    .subscribe(RES => {
        console.log(RES);
    });

If you want to execute the observables in sequential, use .concat():

this.service.getAllMessages()
    .flatMap(items => {
        return Observable.concat(...items.map(item => this.apiService.postMessage(item)));
    })
    .subscribe(RES => {
        console.log(RES);
    });

Note the spread operator for .concat.

edited Oct 19, 2017 at 17:17

answered Oct 19, 2017 at 17:02

CozyAzure

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1 Comment

thk Over a year ago

Thanks a lot you saved my day ! (didnt know about the spread operator, happy to learn)

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