flutter firestore stream mapping to another stream

发布于 2020-11-28 03:21:07

I have a menus collection on firestore and I want to perform a map operation on each document and return a new stream. So, instead of the Stream<QuerySnapShop>, I wanted Stream<VendorMenuItem>

  Stream<VendorMenuItem> getAllVendorMenuItems(String vendorId) async* {
    var collectionReference = fs.collection('restaurants').doc('$vendorId').collection("menus").snapshots();
    collectionReference.map((event) {
      print("mapping");

      event.docs.forEach((element) {
        return VendorMenuItem.fromMap(element.data());
      });
    });
  }

and I am calling it within a build method just to test my approach, and I got nothing printed on the console, here is how I called it

@override
  Widget build(BuildContext context) {
    var fs = Provider.of<FireStoreDatabaseRoute>(context);

    fs.getAllVendorMenuItems("ewP3B6XWNyqjM98GYYaq").listen((event) {
      print("printing  final result");
      print(event.name);
    });

Any clues? thank you

UPDATE:

I wasn't yielding anything, however the yield keyword didnt help

  Stream<VendorMenuItem> getAllVendorMenuItems(String vendorId) async* {
    var collectionReference = FirebaseFirestore.instance.collection('restaurants').doc('$vendorId').collection("menus").snapshots();
    yield* collectionReference.map((event) => event.docs.map((e) => VendorMenuItem.fromMap(e.data())));
  }

Questioner

Brendon Cheung

Viewed

Original

Stream<List<VendorMenuItem>> getAllVendorMenuItems(String vendorId) async* { var collectionReference = FirebaseFirestore.instance.collection('Files').snapshots(); yield* collectionReference.map( (event) => event.docs .map( (e) => VendorMenuItem.fromMap(e.data()), ) .toList(), //Added to list to Match the type, other wise dart will throw an error something Like MappedList is not a sub type of List ); }

Stream<List<VendorMenuItem>> getAllVendorMenuItems2(String vendorId) { StreamController<List<VendorMenuItem>> controller = StreamController<List<VendorMenuItem>>(); FirebaseFirestore.instance.collection("Files").snapshots().listen((event) { controller.add(event.docs .map( (e) => VendorMenuItem.fromMap(e.data()), ) .toList() //ToList To Match type with List ); }); return controller.stream; }

Brendon Cheung 2020-11-28 03:36:17

error: The type 'Stream<Stream<VendorMenuItem>>' implied by the 'yield' expression must be assignable to 'Stream<VendorMenuItem>'.dart(yield_of_invalid_type)

Taha Malik 2020-11-28 03:38:29

try using yield*

Taha Malik 2020-11-28 03:39:26

but this is not the proper way, let me update my answer.

Brendon Cheung 2020-11-28 03:41:16

please see my new code

Taha Malik 2020-11-28 03:45:56

check my updated code.

flutter firestore stream mapping to another stream

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