不满足条件时取消 Observable 中链答案

【问题标题】：Cancelling an Observable mid-chain when a condition is not met不满足条件时取消 Observable 中链
【发布时间】：2020-09-12 22:59:12
【问题描述】：

是否可以取消中链的 Observable？假设我们有一些相互依赖的事件链，如果一个链发生故障，则无需继续。

observable_1.pipe(
  take(1),
  switchMap((result_1) => {
    // Do something that requires observable_1 and return something
    // If it fails, there is no point to proceed
    // If it succeeds, we can continue
  }),
  switchMap((result_2) => {
    // Do something that requires result_2 and return something
    // If it fails, there is no point to proceed
    // If it succeeds, we can continue
  }),
  // etc...
);

【问题讨论】：

标签： angular typescript rxjs ngrx

【解决方案1】：

因此您可以为此目的使用filter 运算符：

observable_1.pipe(
      take(1),
      switchMap((result_1) => {
      }),
      switchMap((result_2) => {
        // If it fails, there is no point to proceed
        result_2.status = false;
        // If it succeeds, we can continue
        result_2.status = true;
        return result_2;
      }),
      filter(result => result.status)
      // etc...
    );

【讨论】：

【解决方案2】：

看来你需要EMPTY。

observable_1.pipe(
  take(1),
  switchMap((result_1) => {
    // doing something
    if (successful) {
      return of(result_2);
    }
    return EMPTY; // no further emits.
  }),
  // we are here only in cases of result_2. EMPTY won't trigger it.
  switchMap((result_2) => {
    // doing something
    if (successful) {
      return of(result_3);
    }
    return EMPTY; // no further emits.
  }),
  // we are here only in cases of result_3. EMPTY won't trigger it.
);

【讨论】：