adding values to an empty map in dart

Question

please does anyone know how I can add the value coming from a populated map to an already initialized empty map? type 1: This is just an example I am running on a flutter application to try it because of the hot reload feature. It's supposed to return the map in the map as a logged result. it returns an empty list since it is the value of the already initialized map. what I want is for it to return the added value from the map to the empty map and log.

class _ShowAppState extends State<ShowApp> {
  final usermap = {
    'docreference1': {
      'college': 'Engineering',
      'name': 'ola',
    },
    'docreference2': {
      'college': 'Engineering',
      'name': 'ola b',
    },
    'docreference3': {
      'college': 'Engineering',
      'name': 'ola a',
    }
  };
  @override
  Widget build(BuildContext context) {
    final Map<String, String> stud = {};
    // usermap.forEach((key, value) {
    //   final stud = value;
    //   stud;
    // });
    usermap.values.map((values) {
      stud.addAll(values);
    });
    log('=====> $stud');

type 2: since my firebase request returns a map of map since I am querying a list of an object I need to pass the value of the map from Map<String,Map<String, dynamic>> to Map<String, dynamic>. and I can't return the value of .foreach or .map because their return type is null. so I thought to populate an already initialized empty list how can I archive this. without it returning null.

Future<Either<DtFailure, KtList<Student>>> viewAttendance(
      String college, String department, String level) async {
    try {
      final snapshot = await _firebaseDatabase
          .ref()
          .child(
              "studentsDetail/${_firebaseAuth.currentUser?.uid}/$college/$department/$level")
          .orderByKey()
          .get();
      if (snapshot.exists) {
        final KtList<Student> students = KtList.of();
        // final students = DocRef.fromJson(data as Map<String, dynamic>);
        final data = snapshot.value as Map<String, dynamic>;
        data.forEach((key, value) {
          final studentdata = value as Map<String, dynamic>;
          final students = (studentdata)
              .map((key, value) => MapEntry(
                  key, Student.fromJson(value as Map<String, dynamic>)))
              .values
              .toImmutableList();
          students;
        });

        return right(students);
      } else {
        return right(const KtList.empty());
      }
    } on FirebaseException catch (e) {
      if (e.message!.contains('PERMISSION_DENIED')) {
        return left(const DtFailure.insufficientPermission());
      } else {
        return left(const DtFailure.unexpected());
      }
    }
  }

Answer 1

In type 1, what is your expected output? If you want all the value from your key-value pair and store that in a variable then you can do something like this:

final usermap = {
    'docreference1': {
      'college': 'Engineering',
      'name': 'ola',
    },
    'docreference2': {
      'college': 'Engineering',
      'name': 'ola b',
    },
    'docreference3': {
      'college': 'Engineering',
      'name': 'ola a',
    }
  };

final stud = (userMap.values).toList();
print(stud);   // [{college: Engineering, name: ola}, {college: Engineering, name: ola b}, {college: Engineering, name: ola a}]

stud.forEach(print);   /* {college: Engineering, name: ola}
                          {college: Engineering, name: ola b}
                          {college: Engineering, name: ola a} */

Now that you have a List<Map<String, String>> in variable stud, you can easily use the list's index to get the proper Map item.

If you were expecting for an output that looks something like this:

{ 
  college: Engineering, name: ola, 
  college: Engineering, name: ola b, 
  college: Engineering, name: ola a
}

This is not possible as you can't have a Map with 2 or more keys being equal. Keys must be unique.