Access list field from QueryDocumentSnapshot

Issue

I don't know how to access a field that is a list of Strings from QueryDocumentSnapshot object in flutter.

It works if I access the item in the list directly like element['tags'][0] Is there a way to get the 'tags' field to a list of Strings ? Or to get the size of the list to recreate it by separately getting each item?

Future<UserData> getUserData() async {
   QuerySnapshot userExpenses = await getUserExpenses();
   List<Expense> expenses = [];
   userExpenses.docs.forEach((element) {
      Expense e = new Expense();
      e.description = element.get('description');
      e.price = element.get('price');
      e.tags = [];
      e.tags.add(element.get('tags')[0]);
      e.id = element.id;
      expenses.add(e);
   });
   ........
}

Future<QuerySnapshot> getUserExpenses() async {
    return FirebaseFirestore.instance
        .collection('expenses')
        .where('uuid', isEqualTo: FirebaseAuth.instance.currentUser?.uid)
        .get();
}

class Expense {
  late String id;
  late String price;
  late String description;
  late List<String> tags;
}

Solution

From the test I made, it is not necessary to use the add() method to assign element.get('tags') to the e.tags field.

Since you are initializing an array for your e Expense object, you can assign it straight away using the = equal operator.

But, just remember that when you assign a variable, both elements in the assignment has to be of the same type because if you do as the following:

e.tags = doc.get('tags');

You will get this error:

errors.dart:187 Uncaught (in promise) Error: Expected a value of type 'List', but got one of type 'List'

Because List<dynamic> is not a subtype of List<String>

From there, we should cast the List<dynamic> into List<String> to match the type, like this:

e.tags = List<String>.from(doc.get('tags'));

Answered By - Rogelio Monter