传递给 RXJS 中的 switchMap() 时对象数组的奇怪行为

Strange behaviour of an array of objects when passed into switchMap() in RXJS

我有一个简单的目标,即创建一个可以发出世界上所有国家/地区列表的可观察对象。 observable 的类型是 Country[],即存储值被类型化为一个对象数组。但是,当传递给 switchMap 时,它会神奇地转换为类型 Country。我不知道是什么导致了这种行为,如果不是偶然的话,就在我这边。这是有问题的功能:

public getAllCountries(): Observable<Country[]> {

      const getAppState = createFeatureSelector<ServicesState>('services');
      const getCountries = createSelector( getAppState, (state: ServicesState): Country[] => state.countries);
      // as you can see, this is the NGRX store slice that must be of type Observable<Country[]>
      const countriesFromStore$ = this.store.pipe(select(getCountries));

      return countriesFromStore$.pipe(
        // this is the switchMap that causes the error
        switchMap( countries => {
        // this is the return statement that somehow converts an array of objects into a single object??
        if (countries)  { return countries; }
        const countriesFromServer$: Observable<Country[]> = this.http.get<FilteredArrayResponse<Country>>
           (this.baseUrl, this.config.httpGetJsonOptions).pipe(
               tap( result => this.store.dispatch( new LoadCountriesAction(result.data)) ),
               map( result => result.data)
           );
        return countriesFromServer$; })
    );
  }

如果您有任何疑问:

尝试在 switchMap (import { of } from 'rxjs';) 中返回 of(countries)。我认为应该解决它。 switchMap 需要切换到 Observable

import { of } from 'rxjs';
...
switchMap((countries: Country[]) => {
  if (countries) {
    return of(countries);
  }
  ....
})