Guarantee observable subscription finishes before proceeding to next code

问题

I am doing a bit of a cascade delete with multiple service calls. Some of the later subscriptions rely on previous subscriptions to finish. How can I guarantee an subscription finishes before moving onto my next code?

// Need to make sure this code completes
data.forEach(element => {
    this.myService.delete(element.id).subscribe();
});

// Before running this code
this.myService.getAll().subscribe(res => {
        res.data.forEach(element => {
            this.myService.delete(element.id).subscribe();
        });
    }
);

回答1:

A Subscription has a singular purposes: disposing, but you have options:

If you want to subscribe to observables one after another, you can use concat.
If you want to subscribe to multiple observables at the same time and combine the last value of each, you can use forkJoin.
If you want to use yielded value of an observable in another observable, you can use flatMap.

import { forkJoin, interval, concat, of } from "rxjs";
import { first, flatMap } from "rxjs/operators";

var combinedIntervals =
    forkJoin(
        interval(1000).pipe(first()),
        interval(2500).pipe(first())
    ).pipe(
        flatMap(([a, b]) => of(`${a} and ${b}`))
    );

concat(
    combinedIntervals,
    of("after both intervals")
)
.subscribe(
    console.log.bind(console)
);


// 0 and 0
// after both intervals

For you specific case, you'd select your delete operations as observables and then forkJoin them.

var data = [];

var obsBatch1 = data.map(element => myService.delete(element.id));
var obsBatch2 =
    forkJoin(
        obsBatch1,
        elements => elements.map(
            element => myService.delete(element.id)
        )
    );

obsBatch2.subscribe();

This is rxjs@6 syntax. I leave rxjs@5 as an exercise.

来源：https://stackoverflow.com/questions/51047390/guarantee-observable-subscription-finishes-before-proceeding-to-next-code

标签

angular

typescript

rxjs

observable