ForkJoin Observable failing to trigger events

Question

ForkJoin Observable failing to trigger events

Having an issue with implementing forkJoin on two Observables in my code. Despite directly subscribing to them yielding a response, the forkJoin function doesn't seem to be triggering. Any suggestions on what might be causing this?

private data$: Observable<any[]>;
private statuses$: Observable<any[]>;
private queryStream = new Subject<string>();    

....

this.data$ = this.queryStream
    .startWith('')
     .flatMap(queryInput => {
            this.query = queryInput
            return this._companyService.getCompanies(this.queryRequired + ' ' + this.query, this.page, this.sort);
                })
            .share();
    
...

Observable.forkJoin(this.statuses$, this.companies$)
            .subscribe(res => {
                console.log('forkjoin');
                this._countStatus(res[0], res[1]);
            });


// This shows arrays in the console...

this.statuses$.subscribe(res => console.log(res));
this.companies$.subscribe(res => console.log(res));

// In the console
Array[9]
Array[6]

angular typescript rxjs rxjs5

Answer 1

Answer №1

forkJoin only emits when all inner observables have finished processing. For a similar behavior to forkJoin but with just one emission from each source, you can use combineLatest combined with take(1)

combineLatest(
  this.statuses$,
  this.companies$,
)
.pipe(
  take(1),
)
.subscribe(([statuses, companies]) => {
  console.log('forkjoin');
  this._countStatus(statuses, companies);
});

Once both sources emit their values, combineLatest will trigger an emission, and take(1) will immediately unsubscribe after that.

Answer 2

forkJoin only emits when all inner observables have finished processing. For a similar behavior to forkJoin but with just one emission from each source, you can use combineLatest combined with take(1)

combineLatest(
  this.statuses$,
  this.companies$,
)
.pipe(
  take(1),
)
.subscribe(([statuses, companies]) => {
  console.log('forkjoin');
  this._countStatus(statuses, companies);
});

Once both sources emit their values, combineLatest will trigger an emission, and take(1) will immediately unsubscribe after that.

Answer 3

Answer №2

One common issue that arises with the forkJoin function is that it necessitates all source Observables to emit at least one item and for each of them to complete.

Put simply, if neither this.statuses$ nor this.companies$ emit any items until they both reach completion, then the forkJoin will not emit anything.

this.statuses$.subscribe(
    res => console.log(res),
    undefined,
    () => console.log('completed'),
);

Answer 4

One common issue that arises with the forkJoin function is that it necessitates all source Observables to emit at least one item and for each of them to complete.

Put simply, if neither this.statuses$ nor this.companies$ emit any items until they both reach completion, then the forkJoin will not emit anything.

this.statuses$.subscribe(
    res => console.log(res),
    undefined,
    () => console.log('completed'),
);

Answer 5

Answer №3

After encountering issues with the forkJoin method, I was able to successfully address my problem by using the code snippet below. By leveraging the power of mergeMap, you can effectively map the results of the outer subscription to the inner subscription and handle them according to your needs.

this.data$.pipe(
    mergeMap(source => this.details$.pipe(
        map(inner => [source , inner])
        )
    )
).subscribe(([result1 , result2]) => {
    console.log(result1 , result2);
})

Answer 6

After encountering issues with the forkJoin method, I was able to successfully address my problem by using the code snippet below. By leveraging the power of mergeMap, you can effectively map the results of the outer subscription to the inner subscription and handle them according to your needs.

this.data$.pipe(
    mergeMap(source => this.details$.pipe(
        map(inner => [source , inner])
        )
    )
).subscribe(([result1 , result2]) => {
    console.log(result1 , result2);
})

Answer 7

Answer №4

To optimize the execution of asObservable()-like observables, simply add .pipe(take(1)) as a pipe.

forkJoin({
    l0: this._svc.data$.pipe(take(1)),
    l1: this._api.getLogman1(),
    l2: this._api.getLogman2(),
    l3: this._api.getLogman3(),
})
    .pipe(
        takeUntil(this._unsubscribeAll),
    )
    .subscribe(result => {
        console.log(result);
    });

Answer 8

To optimize the execution of asObservable()-like observables, simply add .pipe(take(1)) as a pipe.

forkJoin({
    l0: this._svc.data$.pipe(take(1)),
    l1: this._api.getLogman1(),
    l2: this._api.getLogman2(),
    l3: this._api.getLogman3(),
})
    .pipe(
        takeUntil(this._unsubscribeAll),
    )
    .subscribe(result => {
        console.log(result);
    });

Answer 9

Answer №5

In contrast to subscribe, forkJoin is unable to work in the same way because it does not function based on events.

Subscribe reacts to a next or completed event, whereas forkJoin only triggers once all observables have completed.

Unlike combineLatest, which fires when all observables emit a next or completed event, forkJoin will only fire when all observables emit a completed event.

Hence, if your observables are emitting next events, the code you posted won't work; however, the following code should be effective:

combineLatest([this.statuses$, this.companies$])
        .subscribe(res => {
            console.log('combineLatest');
            this._countStatus(res[0], res[1]);
        });

Referencing the rxjs documentation, for your scenario, combineLastest is the preferred method: https://www.learnrxjs.io/learn-rxjs/operators/combination/forkjoin

Documentation for combineLatest: https://www.learnrxjs.io/learn-rxjs/operators/combination/combinelatest

Further information on Observables and the various events they can trigger: https://rxjs.dev/guide/observable

Answer 10

In contrast to subscribe, forkJoin is unable to work in the same way because it does not function based on events.

Subscribe reacts to a next or completed event, whereas forkJoin only triggers once all observables have completed.

Unlike combineLatest, which fires when all observables emit a next or completed event, forkJoin will only fire when all observables emit a completed event.

Hence, if your observables are emitting next events, the code you posted won't work; however, the following code should be effective:

combineLatest([this.statuses$, this.companies$])
        .subscribe(res => {
            console.log('combineLatest');
            this._countStatus(res[0], res[1]);
        });

Referencing the rxjs documentation, for your scenario, combineLastest is the preferred method: https://www.learnrxjs.io/learn-rxjs/operators/combination/forkjoin

Documentation for combineLatest: https://www.learnrxjs.io/learn-rxjs/operators/combination/combinelatest

Further information on Observables and the various events they can trigger: https://rxjs.dev/guide/observable

Answer 11

Answer №6

The solution I discovered was using the combineLatest operator!

Answer 12

The solution I discovered was using the combineLatest operator!

Answer 13

Answer №7

When using Observable.forkJoin() in Angular, we can combine multiple HTTP requests into a single observable. For example, we can fetch users and customers data simultaneously by calling _someService.getUsers() and _someService.getCustomers().

Here is an example implementation:

Observable.forkJoin([
  _someService.getUsers(),
  _someService.getCustomers(),
])
  .subscribe((data: [Array<User>, Array<Customer>]) => {
    let users: Array<User> = data[0];
    let customer: Array<Customer> = data[1];
  }, err => {
  });

// someService
getUsers(): Observable<User> {
  let url = '/users';
  return this._http.get(url, headers)
    .map(res => res.json());
}

getCustomers(): Observable<Customer> {
  let url = '/customers';
  return this._http.get(url, headers)
    .map(res => res.json());
}

Answer 14

When using Observable.forkJoin() in Angular, we can combine multiple HTTP requests into a single observable. For example, we can fetch users and customers data simultaneously by calling _someService.getUsers() and _someService.getCustomers().

Here is an example implementation:

Observable.forkJoin([
  _someService.getUsers(),
  _someService.getCustomers(),
])
  .subscribe((data: [Array<User>, Array<Customer>]) => {
    let users: Array<User> = data[0];
    let customer: Array<Customer> = data[1];
  }, err => {
  });

// someService
getUsers(): Observable<User> {
  let url = '/users';
  return this._http.get(url, headers)
    .map(res => res.json());
}

getCustomers(): Observable<Customer> {
  let url = '/customers';
  return this._http.get(url, headers)
    .map(res => res.json());
}

ForkJoin Observable failing to trigger events

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

Answer №7

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