Sample flatten list

main.dart

void main() {
  final sampleData = <DayModel>[
    DayModel(0, [
      LearningModel('Sample 0.1'),
      LearningModel('Sample 0.2'),
      LearningModel('Sample 0.3'),
      LearningModel('Sample 0.4'),
    ]),
    DayModel(1, [
      LearningModel('Sample 1.1'),
    ]),
    DayModel(2, [
      LearningModel('Sample 2.1'),
      LearningModel('Sample 2.2'),
      LearningModel('Sample 2.3'),
    ]),
  ];

  print('[trantap] sampleData: $sampleData');

  final resultExtractSimpleWay =
      extractLearningModelSimpleWay(sampleData, 0, 2);
  if (resultExtractSimpleWay == null) {
    print('[trantap] resultExtractSimpleWay: null');
  } else {
    print('[trantap] resultExtractSimpleWay: $resultExtractSimpleWay');
  }

  final resultExtractModernWay =
      extractLearningModelModernWay(sampleData, 0, 2);
  if (resultExtractModernWay == null) {
    print('[trantap] resultExtractModernWay: null');
  } else {
    print('[trantap] resultExtractModernWay: $resultExtractModernWay');
  }

  final resultFlatListSimpleWay = flatListLearningModelSimpleWay(sampleData);
  print('[trantap] resultFlatListSimpleWay: $resultFlatListSimpleWay');

  final resultFlatListModernWay = flatListLearningModelModernWay(sampleData);
  print('[trantap] resultFlatListModernWay: $resultFlatListModernWay');
}

LearningModel? extractLearningModelSimpleWay(
    List<DayModel> data, int dayId, int learnIndex) {
  // TODO(trantap) [chungnt] - Validate data

  for (final row in data) {
    if (row.id == dayId) {
      final learnModels = row.learningModels;
      if (learnModels.length > learnIndex) {
        return learnModels[learnIndex];
      }
      break;
    }
  }

  return null;
}

LearningModel? extractLearningModelModernWay(
    List<DayModel> data, int dayId, int learnIndex) {
  // TODO(trantap) [chungnt] - Validate data

  try {
    // orElse is not able to work under null-safety when list data are non-null list
    final dayModel =
        data.firstWhere((e) => e.id == dayId); // Exception may occur here
    return dayModel.learningModels.length > learnIndex
        ? dayModel.learningModels[learnIndex]
        : null;
  } on StateError catch (_) {
    return null;
  }
}

List<LearningModel> flatListLearningModelSimpleWay(List<DayModel> data) {
  final result = <LearningModel>[];

  for (final row in data) {
    result.addAll(row.learningModels);
  }

  return result;
}

List<LearningModel> flatListLearningModelModernWay(List<DayModel> data) {
  return data.map((e) => e.learningModels).expand((a) => a).toList();
}

class DayModel {
  DayModel(this.id, this.learningModels);

  final int id;

  final List<LearningModel> learningModels;
}

class LearningModel {
  LearningModel(this.sample);

  final String sample;

  Map<String, dynamic> toMap() {
    return {
      'sample': sample,
    };
  }

  @override
  String toString() {
    return '${toMap()}';
  }
}