Ways to generate an observable within a subscribe method

Question

Ways to generate an observable within a subscribe method

I'm struggling to create an observable that retrieves a certain value from a subscriber. Here's the code I've been working on:

canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<boolean> {
    // get route to be activated
    this.routeToActivate = route.routeConfig.path;

    // retrieve user access levels        
    return this._firebase.isUserAdmin          <-- returns Subscription, not Observable
        .map(user => user.access_level)
        .subscribe( access => {
           // Need to return an observable here
        });
}

I've been having trouble finding reliable resources on observables in Angular 2 to guide me. Any assistance with this would be greatly appreciated!

UPDATE -> Working Version

canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<boolean> {
            // get route to be activated
            this.routeToActivate = route.routeConfig.path;

            // retrieve user access levels        
            return this._firebase.isUserAdmin
                .map(user => {
                    let accessLevel = user.access_level;

                    if (accessLevel === 'admin' ) {
                        return true;
                    }

                }).first();
        }

angular typescript rxjs observable

Answer 1

Answer №1

In order to efficiently handle observables in Angular, it is important to understand the difference between using `map` and `subscribe`. When you use `map`, an `Observable` is returned rather than returning the observable directly from `subscribe`.

canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<boolean> {
    // Determine the route to activate
    this.routeToActivate = route.routeConfig.path;

    // Obtain user access levels
    return this._firebase.isUserAdminObservable
        .map(user => {
            // Perform actions here based on user access level
            // user.access_level;
            return true;
         })
        .first(); // Ensure that the observable completes after the first event (often necessary for canActivate)
        // Note that 'first' needs to be imported similarly to 'map'
}

canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<boolean> {
    // Determine the route to activate
    this.routeToActivate = route.routeConfig.path;

    let subject = new Subject();
    
    // Obtain user access levels        
    this._firebase.isUserAdminObservable
        .map(user => {
            let accessLevel = user.access_level; 
            if (accessLevel === 'admin') { 
                subject.emit(true); 
                subject.complete();
            } 
            return user;
        });
        
     return subject;
}

Answer 2

In order to efficiently handle observables in Angular, it is important to understand the difference between using `map` and `subscribe`. When you use `map`, an `Observable` is returned rather than returning the observable directly from `subscribe`.

canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<boolean> {
    // Determine the route to activate
    this.routeToActivate = route.routeConfig.path;

    // Obtain user access levels
    return this._firebase.isUserAdminObservable
        .map(user => {
            // Perform actions here based on user access level
            // user.access_level;
            return true;
         })
        .first(); // Ensure that the observable completes after the first event (often necessary for canActivate)
        // Note that 'first' needs to be imported similarly to 'map'
}

canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<boolean> {
    // Determine the route to activate
    this.routeToActivate = route.routeConfig.path;

    let subject = new Subject();
    
    // Obtain user access levels        
    this._firebase.isUserAdminObservable
        .map(user => {
            let accessLevel = user.access_level; 
            if (accessLevel === 'admin') { 
                subject.emit(true); 
                subject.complete();
            } 
            return user;
        });
        
     return subject;
}

Answer 3

Answer №2

If you're looking to subscribe to an observable, manipulate the outcome, and then return the modified result within the same subscription, follow these steps:

function xyz(): Observable<any> { 
    const data = fetchDataAndReturnObservable().pipe(map(response => {
          // Implement any desired processing on the response //
          return response; // Return the processed result.
       }
    ))
   return data;
}

Answer 4

If you're looking to subscribe to an observable, manipulate the outcome, and then return the modified result within the same subscription, follow these steps:

function xyz(): Observable<any> { 
    const data = fetchDataAndReturnObservable().pipe(map(response => {
          // Implement any desired processing on the response //
          return response; // Return the processed result.
       }
    ))
   return data;
}

Answer 5

Answer №3

Is it possible to utilize the pipe function along with map from the

import { map } from 'rxjs/operators';

statement?

import { map } from 'rxjs/operators';

@Injectable({
  providedIn: 'root'
})
export class SearchHostService {
  constructor(private readonly http: HttpClient) {}

  searchForHosts(searchString: string): Observable<Employee[]> {
    return this.http
      .get<Employee[]>('./assets/host-users.json')
      .pipe(
        map(employees =>
          employees.filter(({ displayName }) =>
            displayName.toLowerCase().startsWith(searchString),
          ),
        ),
      );
  }
}

Answer 6

Is it possible to utilize the pipe function along with map from the

import { map } from 'rxjs/operators';

statement?

import { map } from 'rxjs/operators';

@Injectable({
  providedIn: 'root'
})
export class SearchHostService {
  constructor(private readonly http: HttpClient) {}

  searchForHosts(searchString: string): Observable<Employee[]> {
    return this.http
      .get<Employee[]>('./assets/host-users.json')
      .pipe(
        map(employees =>
          employees.filter(({ displayName }) =>
            displayName.toLowerCase().startsWith(searchString),
          ),
        ),
      );
  }
}

Answer 7

Answer №4

To transform the Observable object into a promise, you can utilize the toPromise method. Below is an example of how this code can be implemented:

canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Promise<boolean> {
        // Obtain the route to activate
        this.routeToActivate = route.routeConfig.path;

        // Retrieve user access levels        
        return this._firebase.isUserAdmin
            .map(user => {
                return (user.access_level === 'admin');
            }).toPromise();
    }

Answer 8

To transform the Observable object into a promise, you can utilize the toPromise method. Below is an example of how this code can be implemented:

canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Promise<boolean> {
        // Obtain the route to activate
        this.routeToActivate = route.routeConfig.path;

        // Retrieve user access levels        
        return this._firebase.isUserAdmin
            .map(user => {
                return (user.access_level === 'admin');
            }).toPromise();
    }

Answer 9

Answer №5

If you're looking to filter with a predicate and apply a projection function for the first element, this code snippet has got you covered.

canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<boolean> {
    this.routeToActivate = route.routeConfig.path;      
    return this._firebase.isUserAdminObservable
        .first((_, index) => index === 0, user => {
           // Add your logic here
           // user.access_level;
           return true;
         })
}

Answer №6

To trigger an event based on the access level, you can create a new observable.

canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<boolean> {
    // Retrieve route to activate
    this.routeToActivate = route.routeConfig.path;

    // Obtain user access levels
    return new Observable(subscriber=>{
       this._firebase.isUserAdmin
        .map(user => user.access_level)
        .subscribe(access => {
           // Create and return an observable based on logic conditions
           // Modify your logic here...
           return access === XXX ? subscriber.next(true) : subscriber.next(false);
        }, err => subscriber.error());
    })
}

For more information, visit: https://rxjs-dev.firebaseapp.com/guide/observable

Answer 12

To trigger an event based on the access level, you can create a new observable.

canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<boolean> {
    // Retrieve route to activate
    this.routeToActivate = route.routeConfig.path;

    // Obtain user access levels
    return new Observable(subscriber=>{
       this._firebase.isUserAdmin
        .map(user => user.access_level)
        .subscribe(access => {
           // Create and return an observable based on logic conditions
           // Modify your logic here...
           return access === XXX ? subscriber.next(true) : subscriber.next(false);
        }, err => subscriber.error());
    })
}

For more information, visit: https://rxjs-dev.firebaseapp.com/guide/observable

Ways to generate an observable within a subscribe method

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

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