Monitoring real-time updates in Angular components using Firebase

Question

Monitoring real-time updates in Angular components using Firebase

I am looking to access data across multiple components and have implemented a service to retrieve the necessary data. However, I am encountering an issue when attempting to observe this data. Here is my current code:

@Injectable()
export class NotificationsService {

    constructor(private af: AngularFireDatabase) {}

    public retrieveNotifications(): Observable<NotificationObj[]> {
      return this.af.database.ref(refs.NOTIFICATIONS).on('value', snap => {
        const data = snap.val();
        return Object.keys(data).map(key => {
          return new NotificationObj(key, data[key]);
        });
      })
    }
}

Upon running this code, I receive the following error message:

TS2322: Type '(a: DataSnapshot, b?: string) => any' is not assignable to type 'Observable<NotificationObj[]>'. Property '_isScalar' is missing in type '(a: DataSnapshot, b?: string) => any'.

I am seeking guidance on how to modify my method in order to handle data parsing within the service itself while still being able to listen for changes from components.

angular typescript firebase

Answer 1

Answer №1

After searching extensively, I came across the solution provided in this Stack Overflow thread addressing a Firebase error related to subscribing to ref.on('value', callback)

The complete code snippet is shown below:

public retrieveNotifications(): Observable<NotificationObj[]> {
  return Observable.create(subscriber => {
    const ref = this.af.database.ref(refs.NOTIFICATIONS);
    const callback = ref.on('value', snap => {
      const data = snap.val();
      const notifications = Object.keys(data).map(key => {
        return new NotificationObj(key, data[key]);
      });
      subscriber.next(notifications);
    });
    return () => ref.off('value', callback);
  })
}

Answer 2

After searching extensively, I came across the solution provided in this Stack Overflow thread addressing a Firebase error related to subscribing to ref.on('value', callback)

The complete code snippet is shown below:

public retrieveNotifications(): Observable<NotificationObj[]> {
  return Observable.create(subscriber => {
    const ref = this.af.database.ref(refs.NOTIFICATIONS);
    const callback = ref.on('value', snap => {
      const data = snap.val();
      const notifications = Object.keys(data).map(key => {
        return new NotificationObj(key, data[key]);
      });
      subscriber.next(notifications);
    });
    return () => ref.off('value', callback);
  })
}

Monitoring real-time updates in Angular components using Firebase

Answer №1

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