Question 305199 in Flutter Question posted in
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Flutter – type 'Future<List<SurveyData>>' is not a subtype of type 'List<SurveyData>' in type cast (DART)

I’m trying to retrieve data from a database, and have made these two methods inside of a certain "TodoDB" class:

  Future<List<SurveyData>> fetchAll() async {
    final database = await DatabaseService().database;
    final survey = await database.rawQuery('''SELECT * from $tableName''');
    return survey.map((survey) => SurveyData.fromSqfliteDatabase(survey)).toList();
  }

  Future<SurveyData> fetchById(int id) async {
    final database = await DatabaseService().database;
    final survey = await database.rawQuery('''SELECT * from $tableName WHERE id = ?''', [id]);
    return SurveyData.fromSqfliteDatabase(survey.first);
  }

later on, I call the upper methods in this other class:

class SurveyUtilities {

  final todoDB = TodoDB();

  /// function that retrieves and parses all surveys data from database *
  Future<List<SurveyData>> getSurveys() async {
    return todoDB.fetchAll();
  }

  /// function that retrieves and parses a certain survey data from database *
  Future<SurveyData> getSurveyData(int id) async {
    return todoDB.fetchById(id);
  }

}

I tried a bunch of solutions online, but I always get this error message:
"type ‘Future<List>’ is not a subtype of type ‘List’ in type cast".

I’ve also tried writing the getSurveys() method like this:

  Future<List<SurveyData>> getSurveys() async {
    final allSurveys = await todoDB.fetchAll();
    return allSurveys;
  }

but the result is always the same.

I haven’t worked with dart, databases or sql before, so I apologize if there’s some obvious mistakes (I’m still learning!)

For context, my SurveyDaya is formatted as follows:

  SurveyData({required this.id, required this.title, required this.description, required this.questions});

  factory SurveyData.fromSqfliteDatabase(Map<String, dynamic> map) => SurveyData(
    id: map['id']?.toInt() ?? 0,
    title: map['title'] ?? '',
    description: map['description'] ?? '',
    questions: map['questions'] ?? '',
  );
Tags:

2

Answers


  1. 0

    You should update SurveyUtilities class like this, it will solve issue

    class SurveyUtilities {

  final todoDB = TodoDB();

  /// function that retrieves and parses all surveys data from database *
  Future<List<SurveyData>> getSurveys() async {
    return await todoDB.fetchAll(); //you must have to use await before calling method
  }

  /// function that retrieves and parses a certain survey data from database *
  Future<SurveyData> getSurveyData(int id) async {
    return await todoDB.fetchById(id); //you must have to use await before calling method
  }

}
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  2. 0

    You should remove the "Future" from the return type of the getSurveys function because it is unnecessary. The updated method will be like this:

    List<SurveyData> getSurveys() async {
    return await todoDB.fetchAll();
}

    And wherever you are calling this function to initialize the list for UI will be used liked this:

    final listOfSurveys = SurveyUtilities().getSurveys();
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