避免在Angular 2+中嵌套订阅? [英] Avoiding nesting subscriptions in Angular 2+?

问题描述

我有2个端点:

• 1个端点来记录当前用户.
• 1个端点来获得该用户的授权.

我实际上使用:

this.user
  .subscribe((e) => {
     this.grants.get(e)
        .subscribe((x) => {
            console.log(x)
         })
  })

但这是Angular 2 +/RxJS的反模式.

But this is an anti-pattern of Angular 2+/RxJS.

我想知道如何遵循Angular/RxJS最佳实践.

I would like to know how to do this following Angular/RxJS best practices.

谢谢

推荐答案

避免嵌套订阅取决于可观察对象的性质以及它们如何相互依赖:

Avoiding nested subscriptions depends on the nature of the observables and how they depend on each other:

当可观察对象( this.grants.get())依赖于另一个可观察对象( this.user )的通知时，可以使用任何更高版本的RxJS订单映射运算符 switchMap ， mergeMap ， concatMap 和 exhaustMap .每个人都有自己的目的.您可以在此处找到它们之间的区别.

When an observable (this.grants.get()) depends on the notification from another observable (this.user), you could use any of the RxJS higher order mapping operators switchMap, mergeMap, concatMap and exhaustMap. Each has their own purpose. You could find the differences between them here.

他们之间的简短差异

• switchMap -如果外部可观察到的发射，则取消内部可观察到的
• mergeMap -触发每个外部通知的内部观察(展平外部通知)
• concatMap -本质上是 mergeMap ，可以随时具有单个并发请求(展平外部通知，但按顺序发出)
• exhaustMap -如果内部可观察项尚未完成，则忽略外部通知

• switchMap - cancel inner observable if the outer observable emits
• mergeMap - trigger inner observable for each outer notification (flatten the outer notifications)
• concatMap - essentially mergeMap with single concurrent request at any time (flattens the outer notifications but emit them in order)
• exhaustMap - ignore outer notifications if inner observable hasn't completed

使用 switchMap 运算符

this.user.pipe(
  switchMap(e => this.grants.get(e))
).subscribe((x) => {
  console.log(x)
});

独立的可观察物

如果可观察对象彼此独立，则可以使用RxJS函数(例如 forkJoin ， combineLatest 或 zip )并行触发可观察对象

Independent observables

If the observables are independent of each other, you could use RxJS functions like forkJoin, combineLatest or zip to trigger the observables in parallel.

他们之间的简短差异

• forkJoin ^α-仅在所有可观察项完成时发出
• combineLatest ^α，β-当任何个可观察对象发出时发出(不包含任何可观察到的可观察对象将发出旧值)
• zip ^α，β-在所有所有可观察物发射时发射

• forkJoin^α - emit only when all the observables complete
• combineLatest^α,β - emit when any of the observables emit (observables w/o emissions will emit old value)
• zip^α,β - emit when all of the observables emit

使用 forkJoin

forkJoin(this.obs1, this.obs2, ...).subscribe(
  res => console.log(res)
);

α-从每个可观察对象发出一系列通知(例如，(this.obs1，this.obs2，...)将发出 ['res from obs1"，"res from obs2"，...] ).

α - emits an array of notifications from each observable (eg. (this.obs1, this.obs2, ...) will emit ['res from obs1', 'res from obs2', ...]).

β-所有可观察物应该至少发射一次，以供操作员发射

β - all observables should emit atleast once for the operator to emit

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