Angular 2 Firebase Observable to promise doesn't return anything

Question

I\'m currently working on an Angular 2 project with AngularFire2 and I\'m trying to convert a FirebaseListObservable to a Promise. I know that it doesn\'t make much sense si

Answer 1

The problem is that the toPromise operator converts the observable to a promise that resolves to the observable's final value. That means the observable must complete before the promise resolves.

In AngularFire2, list and object observables don't complete; they re-emit whenever the database changes.

You can solve the problem using the first operator, which takes the first emitted value and then completes the composed observable:

import 'rxjs/add/operator/first';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/toPromise';
...
return this._af.database
  .list('users')
  .map(users => {

    let exists = false;
    users.forEach(user => {
      if (user.name.toLowerCase() === name.toLowerCase()) {
        console.log('Name already exists!');
        exists = true;
      }
    });
    return exists;
  })
  .first()
  .toPromise();