RxJ：一个接一个地执行3个可观察对象，并使用第一个请求，第二个请求和第三个请求的结果

Question

I need to be able to execute 3 observables one after another so that I can use result value from 1st one in second and also 1st and 2nd result in the third one.

Something like this ( it doesn't work as the serviceId is not visible in the third request ):

private setupStuff(): void {
        this.initRouteParams().pipe(
            switchMap(serviceId => this.getFileInfo(serviceId)),
            switchMap(fileName => this.getExistingFile(serviceId, fileName)
                .subscribe(response => {
                    console.log(response);
                }))
            );
    }

Answer 1

You can explicitly return the value of the serviceN to the serviceN+1. Here's the idea :

private setupStuff() {
  this.initRouteParams()
    .pipe(
      switchMap(serviceId => {
        return zip(of(serviceId), this.getFileInfo(serviceId))
      }),
      switchMap(([serviceId, filename]) => {
        return zip(of(serviceId), of(filename), this.getExistingFile(serviceId, filename))
      })
    )
    .subscribe(([serviceId, filename, response]) => {
      console.log(serviceId, filename, response);
    })
}

Edit:

You can fix types errors by explicitly declare types of each input. You probably want to assign the appropriate type for response .

Answer 2

managed to solve it like this:

private checkFilePresence(): void {
        const first$: Observable<string> = this.initRouteParams();
        const second$: Observable<string> = first$.pipe(
            switchMap(config => {
                return this.getFileInfo(config);
            })
        );
        const third$: Observable<CkitExistingFileResponse> = combineLatest(first$, second$).pipe(
            switchMap(([config, second]) => {
                return this.getExistingFile(config, second);
            })
        );
        combineLatest(first$, third$)
            .subscribe(() => {
            });
    }

Answer 3

You can subsribe to observables in sequence as below:

private setupStuff(): void {
        this.initRouteParams().subscribe( serviceId => {
            this.getFileInfo(serviceId).subscribe(fileName => {
               this.getExistingFile(serviceId, fileName).subscribe( response => {
                   console.log(response);
                });
            });
        });
}