Ngrx @Effects - 立即停止

Question

我有下面的ngrx效果。 "map"里面我有个条件。如何不继续mergeMap就立即停止效果

@Effect()
myEffect$: Observable < Action > = this.actions$.pipe(
  ofType('INIT_ACADEMY_DOMAIN'),
  map((action: any) => {
    const url = 'http://www.academy.xyzq';
    if (1 === 1) {
      // Make this effect stop immediately and do nothing more
    }
    action.url = url;
    return action;
  }),
  mergeMap((action: any) =>
    this.http.get(action.url).pipe(
      switchMap((data: any) => {
        return [{
          type: 'INIT_ACADEMY',
          payload: {
            academy: data.academy
          }
        }];
      })
    )),
  catchError(() => of ({
    type: 'INIT_IT_FAILED'
  }))
);

Answer 1

You can try like this.

@Effect()
myEffect$: Observable < Action > = this.actions$.pipe(
  ofType('INIT_ACADEMY_DOMAIN'),
  map((action: any) => {
    const url = 'http://www.academy.xyzq';
    if (1 === 1) {
      // Make this effect stop immediately and do nothing more
      return null;
    }
    action.url = url;
    return action;
  }),
  mergeMap((action: any) =>
    if(action){
    return this.http.get(action.url).pipe(
      switchMap((data: any) => {
        return [{
          type: 'INIT_ACADEMY',
          payload: {
            academy: data.academy
          }
        }];
      })
      } else{
        return null;
      }
    )),
  catchError(() => of ({
    type: 'INIT_IT_FAILED'
  }))
);

Answer 2

您应该考虑使用 filter 函数根据您的条件过滤掉操作：

@Effect()
myEffect$: Observable < Action > = this.actions$.pipe(
  ofType('INIT_ACADEMY_DOMAIN'),
  filter((x) => 1 === 1),
  mergeMap((action: any) =>
    this.http.get(action.url).pipe(
      switchMap((data: any) => {
        return [{
          type: 'INIT_ACADEMY',
          payload: {
            academy: data.academy
          }
        }];
      })
    )),
  catchError(() => of ({
    type: 'INIT_IT_FAILED'
  }))
);

或者，如果您的条件为真，您可以只分派一个新操作，并创建一个更简单的效果来执行 mergeMap 函数中的部分。

你应该尽量让你的效果尽可能简单。如果您的效果进行大量逻辑/条件检查，则很难找到一个合适的名称来描述效果的实际作用。