在继续执行下一个代码之前，确保可观察到的订阅完成 [英] Guarantee observable subscription finishes before proceeding to next code

问题描述

我正在通过多个服务调用进行级联删除.某些更高版本的订阅依赖于先前的订阅来完成.我该如何保证订阅完成才能进入下一个代码?

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();
        });
    }
);

推荐答案

Subscription具有一个单一目的:处置，但是您可以选择:

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

• 如果您要一个又一个地订阅可观察的数据，可以使用 concat .

如果要同时订阅多个可观察对象并合并每个对象的最后一个值，则可以使用

If you want to subscribe to multiple observables at the same time and combine the last value of each, you can use forkJoin.

如果要在另一个可观测值中使用一个观测值的屈服值，则可以使用flatMap.

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

---

对于您的特定情况，您将选择删除操作作为可观察对象，然后forkJoin加入它们.

---

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();

---

这是rxjs@6语法.我将rxjs@5留作练习.

---

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

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