angular - Firestore + AngularFire2 pagination ( query items by range - .startAfter(lastVisible) )

Question

In a component I want to pull a range of items from FireStore, for ex. from 0 to 5, from 5 to 10 etc. I found this in FireStore's docs, but they dont use AngularFire2 so as harder I tried to refactor as bigger mess I got. I made it working by simply splice()'ing:

service ->

topFirstScores(): AngularFirestoreCollection<Score> {
  return this.fireRef.collection('scores', r => r
          .orderBy('score', 'desc').limit(6)
  );
}

component ->

$scores = new Subject();

this.scores$ = this.$scores.asObservable();
if (this.scores === 'first') {
  this.scoreS.topFirstScores().valueChanges().take(1)
    .subscribe(_ => this.$scores.next(_.splice(0, 3)))
} else {
  this.scoreS.topFirstScores().valueChanges().take(1)
    .subscribe(_ => this.$scores.next(_.splice(3, 3)))
}

But this seems more as a workaround. Could anyone translate this:

var first = db.collection("cities")
        .orderBy("population")
        .limit(25);

return first.get().then(function (documentSnapshots) {
  // Get the last visible document
  var lastVisible = documentSnapshots.docs[documentSnapshots.docs.length-1];
  console.log("last", lastVisible);

  // Construct a new query starting at this document,
  // get the next 25 cities.
  var next = db.collection("cities")
          .orderBy("population")
          .startAfter(lastVisible)
          .limit(25);
});

That preferably returns AngularFirestoreCollection<T>?

Answer 1

Waitting for answers