Flutter Streambuilder stuck in connectionstate.waiting

Question

i have a problem with a Flutter application. I want to receive data from a firebase firestore by an Document id. The problem is, i cant replicate the data in one collection, so i have to use two collections.

My data ist a Measurement(String, String,..., List) MeasurementData(String,String,Number)

As far as i understand the Firestore i cant make such a list in one collection, so i have created a second one in whitch each document consists of three arrays. I also save the id from the Measurement Document where it belongs to. To use it in Flutter a use a StreamBuilder widget. For easer access i convert the document bevor using into a Dart Object. Because i have two Streams which should be converted to one Object i have a predessecor StreamMeasurement object which is basicly the same as the Measurement Object, but without the MeasurementData list, because this first needs to be created, instead it only saves a id for the measurementData Document. After that i use the Rx.zip2 to create an Measurement Object from the StreamMeasurement Object and add the List to have a complete object.

    Class Service
    
    /// The firebase instance
    FirebaseFirestore db = FirebaseFirestore.instance;
    
    ///Finds and returns a [Measurement] by its [id]
    Stream<Measurement> getById(String id) {
    Stream<StreamMeasurement> streamMeasurementStream =db.collection("measurements").doc(id)
         .snapshots().map((document) => StreamMeasurement.fromJson(document.data()!));
    return Rx.zip2(streamMeasurementStream, getMeasurementDataStreamById(id)
            , (StreamMeasurement streamMeasurement, List<MeasurementData> measurementData) {
                  Measurement measurement = Measurement.fromStreamMeasurement(streamMeasurement, measurementData);
                  if(measurement == null)
                  {
                      //TODO Write a concrete exception to throw and catch
                      throw Exception('Measurement Stream is null');
                  }
                  return measurement;
          }) ;
      }

     /// Returns a [Stream<List<MeasurementData>>] for a given Measurement id
    Stream<List<MeasurementData>> getMeasurementDataStreamById(String id)
      {
        return db.collection("measurementData").where("measurement", isEqualTo: id).
         snapshots().
         map((querySnapshot) => querySnapshot.docChanges)
        .expand((changes) => changes)
        .map((change) => change.doc).map((document) => MeasurementData.fromJson(document.data()!));
       }

    Class DetailScreen
    @override
    Widget build(BuildContext context) {
        MeasurementService measurementService = MeasurementService();
        Stream<Measurement> measurementstream = measurementService.getById(
        "GmfzveKeozkcfdlrk75s");
        return StreamBuilder<Measurement>(
            stream: measurementstream,
            builder: (BuildContext context, AsyncSnapshot<Measurement> snapshot) {
            if (snapshot.hasError) {
                print(snapshot.error);
                return Text('Something went wrong' + snapshot.error.toString());
            } 

            if (snapshot.connectionState == ConnectionState.waiting) {
               print(snapshot);
               return Text("Loading" + snapshot.connectionState.toString());
             }
             Measurement? measurement = snapshot.data;
             return SafeArea(

Print(snapshot) => I/flutter (19335): AsyncSnapshot(ConnectionState.waiting, null, null, null)

The result is, that the StreamBuilder is stuck in ConnectionState.waiting state if i use the getById(id) function

Answer 1

Okay, ... Question solved. The problem was a unmatched whitespace before the id EDIT: I had hardcodet the ID manually in the database, while writing i had left an whitespace before id, that doesnt belongs there and so the request doesnt work like " 1234" should be "1234"