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

Question

RxJS 初学者在这里。我正在使用 Angular 6，并试图弄清楚如何Observable<T>从Observable<Observable<T>>. 我不确定这是否有效，并且我正在努力从概念上理解它，但这似乎是一个简单的问题。

我研究过 switchMap、flatMap、forJoin，但我认为它们不符合我的需求。

我想做的是 Angular 路由防护，它将阻止用户访问路由，除非他们拥有必要的权限。2 个依赖项是从中获取信息的用户配置文件，然后用于获取其权限。这种混合导致了 Observable of Observable 问题。这是我所得到的：

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

就目前而言，您将从hasPermissionObservable函数返回一个 Observable，它将被包装在map operator.

您会想查看mergeMap/flatMap operator或contactMap operator。

MergeMap：当您希望展平内部可观察值但想要手动控制内部订阅的数量时，最好使用此运算符。Learn RXJS 链接中的示例：

// 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：将值映射到内部可观察对象，按顺序订阅和发出。Learn RXJS 链接中的示例：

// 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)
);

所以对于你的例子：

/**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;
}