Observable<Observable<T>>到Observable<T>

Question

这里是RxJS初学者。我正在使用角6，并试图找出如何从Observable<T>从Observable<Observable<T>>。我不确定这是否有效，我很难从概念上理解它，然而这似乎是一个简单的问题。

我研究过switchMap，flatMap，forJoin，但是我认为它们不适合我的需要。

我试图做的是一个角度路由保护，这将阻止用户访问一个路由，除非他们有必要的权限。2依赖项是一个用户配置文件，用于获取他们的信息，然后用于获取他们的权限。这种混合导致了可观察到的问题。我要说的是：

export class AuthPermissionsRouteGuard implements CanActivate {
    constructor(
    private router: Router,
    private authService: AuthPermissionsService,
    private openIdService: AuthOpenIdService) {}
    
    /**Navigates to route if user has necessary permission, navigates to '/forbidden' otherwise */
    canActivate(routeSnapshot: ActivatedRouteSnapshot): Observable<boolean> {
        return this.canNavigateToRoute(routeSnapshot.data['permissionId'] as number);
    }

    /**Waits on a valid user profile, once we get one - checks permissions */
    private canNavigateToRoute(permissionId: number): Observable<boolean> {
        const observableOfObservable = this.openIdService.$userProfile
            .pipe(
                filter(userProfile => userProfile ? true : false),
                map(_ => this.hasPermissionObservable(permissionId)));

            // Type Observable<Observable<T>> is not assignable to Observable<T> :(
        return observableOfObservable;
    }

    /**Checks if user has permission to access desired route and returns the result. Navigates to '/forbidden' if no permissions */
    private hasPermissionObservable(permissionId: number): Observable<boolean> {
        return this.permissionsService.hasPermission(permissionId).pipe(
            map(hasPermission => {
                if (!hasPermission) {
                    this.router.navigate(['/forbidden']);
                }

                return hasPermission;
            }
        ));
    }
}

Answer 1

现在，您将从hasPermissionObservable函数返回一个可观测的，该函数将被包装在一个可从map operator中观察到的函数中。

您将需要查看mergeMap/flatMap operator或contactMap operator。

MergeMap:当您希望将内部可观察到的内容扁平化时，最好使用此操作符，但希望手动控制内部订阅的数量。来自Learn链接的示例：

// RxJS v6+
import { of } from 'rxjs';
import { mergeMap } from 'rxjs/operators';

// emit 'Hello'
const source = of('Hello');
// map to inner observable and flatten
const example = source.pipe(mergeMap(val => of(`${val} World!`)));
// output: 'Hello World!'
const subscribe = example.subscribe(val => console.log(val));

ContactMap:按顺序将值映射到内部可观测、订阅和发出。来自Learn链接的示例：

// RxJS v6+
import { of } from 'rxjs';
import { concatMap } from 'rxjs/operators';

// emit 'Hello' and 'Goodbye'
const source = of('Hello', 'Goodbye');
// example with promise
const examplePromise = val => new Promise(resolve => resolve(`${val} World!`));
// map value from source into inner observable, when complete emit result and move to next
const example = source.pipe(concatMap(val => examplePromise(val)));
// output: 'Example w/ Promise: 'Hello World', Example w/ Promise: 'Goodbye World'
const subscribe = example.subscribe(val =>
  console.log('Example w/ Promise:', val)
);

因此，对于你的例子：

/**Waits on a valid user profile, once we get one - checks permissions */
private canNavigateToRoute(permissionId: number): Observable<boolean> {
  const observableOfObservable = this.openIdService.$userProfile
    .pipe(
       filter(userProfile => userProfile ? true : false),
       concatMap(_ => this.hasPermissionObservable(permissionId))); // <- try changes here

  // Type Observable<Observable<T>> is not assignable to Observable<T> :(
  return observableOfObservable;
}