Flutter-Firestore transform Stream>>> into List

Question

I made a function where I want to return all places in my database which are inside a radius. Thats why Im using GeoFlutterFire. My problem its that I dont know how to convert Stream<List<DocumentSnapshot<Map<String, dynamic>>>> into a List<> of my Class type.


import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:geoflutterfire/geoflutterfire.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:firebase_storage/firebase_storage.dart';
import 'package:uerto/models/index.dart';

class SearchApi {
  const SearchApi({required FirebaseAuth auth, required FirebaseFirestore firestore, required FirebaseStorage storage, required Geoflutterfire geo})
      : _auth = auth,
        _firestore = firestore,
        _storage = storage,
        _geo = geo;

  final FirebaseAuth _auth;
  final FirebaseFirestore _firestore;
  final FirebaseStorage _storage;
  final Geoflutterfire _geo;

  Future<List<AppClient>> getClientList() async{

    final List<AppClient> newResult = <AppClient>[];

    final GeoFirePoint center = _geo.point(latitude: 44.414445, longitude: 26.01135501);

    final CollectionReference<Map<String, dynamic>> collectionReference = _firestore.collection('clients/London/Beauty');

    final double radius = 5000;
    const String field = 'point';

    final  Stream<List<DocumentSnapshot<Map<String, dynamic>>>> stream = _geo.collection(collectionRef: collectionReference).within(center: center, radius: radius, field: field);

    ///something to transform Stream<List<DocumentSnapshot<Map<String, dynamic>>>> stream into List<AppClient> result;

    newResult.addAll(result);

    return newResult;

  }
}

Maybe just access a moment in the stream to grab one list at a time. Because your stream isn't a list. You could maybe chunk the stream into smaller list records, if you don't need it to stay in one object. — Micah, Sep 16 '21 at 13:42
see `Stream.first` property for example - the docs say: *"The first element of this stream. Stops listening to this stream after the first element has been received."* — pskink, Sep 16 '21 at 14:00

score 1 · Accepted Answer · answered Sep 16 '21 at 15:57

stream.listen((List<DocumentSnapshot> documentList) {
  // this function would be called when ever documentList changes.
  // So, it might be called even after your getClientsList() is completed.
  List<Map<String, dynamic>> newResult = documentList.map((e) => e.data()).toList();
});

Since getClientsList returns a future, you might want to convert the stream to a future. In that case, you can use this.

List<Map<String, dynamic>> newResult = (await stream.first).map((e) => e.data()).toList();

Alternatively, you can listen to the stream using a stream builder. Something like this.

StreamBuilder<DocumentSnapshot>(
  stream: _geo.collection(collectionRef: collectionReference)
      .within(center: center, radius: radius, field: field),
  builder:
      (BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
    if (snapshot.hasError) return Text('Something went wrong');
    if (snapshot.connectionState == ConnectionState.waiting)
      return CircularProgressIndicator();

    List<Map<String, dynamic>> newResult = snapshot.data.data();
    print(newResult);
    return SizedBox();
  },
)

jwehrle · Answer 2 · 2021-09-16T17:19:59.607

Streams are really useful and offer, out-of-the-box, a lot of elegant solutions.

In your case I would use a StreamTransformer to do something like this:

Stream<CustomType> stream = _geo.collection(collectionRef: collectionReference)
   .within(center: center, radius: radius, field: field)
   .transform(StreamTransformer.fromHandlers(handleData: (docSnap, sink) {
      if (docSnap.exists) {
         sink.add(<convert docSnap fields to CustomType here>);
      }
}));

You can do a lot more with Streams and StreamTransformers that make your code easier to read and debug and just, well, prettier. Documentation about StreamTransformers: https://api.flutter.dev/flutter/dart-async/StreamTransformer-class.html

Edit: disclaimer, this answer is based on the Stream file classes and not geo flutter fire - of which I have no experience.

Flutter-Firestore transform Stream>>> into List

2 Answers2