Flutter and Sembast - Method returns null - flutter

Question

I try to combine flutter with the sembast nosql database. I created a method to get all db documents and edit the given data.
My method looks like this:
Future<List<Minute>> getAll() async {
final finder = Finder(sortOrders: [SortOrder('timestamp')]);
final recordSnapshots = await store.find(await _db, finder: finder);
return recordSnapshots.map((snapshot) {
final minute = Minute.fromMap(snapshot.value);
minute.id = snapshot.key;
return minute;
}).toList();
}
get getSum {
getAll().then((value) {
int total = value.fold(
0, (previousValue, element) => previousValue + element.value);
print(total); // The correct value
return total; // Here I dont retrieve the value
});
}
print(total) shows me the right value, but in the Widget I don´t retrieve it. I retrieve just null. Whats the issue here?

Answer 1

I think you should not return a value inside the then(...) maybe return just the future and use a FutureBuilder as widget

Answer 2

You should use pedantic/strong mode as it should show lint warnings (missing return type and missing return value) that could help solving your issue without running it.
Unoptimized solution based on your code:
Future<int> getSum() async {
var minutes = await getAll();
var total = minutes.fold<int>(
0, (previousValue, element) => previousValue + element.value);
return total;
}
Possible optimizations:
avoid the sort order when computing the sum
only read the value field instead of converting the whole object
Example:
Future<int> getSum() async {
var total = 0;
(await store.find(await _db)).forEach((snapshot) {
total += snapshot['value'] as int;
});
return total;
}
Unfortunately the return value cannot be a String, it could be a Future<String> though (i.e. db calls are async).
as Julian2611 noted you then need to use a FutureBuilder and for example .toString() to convert the value to a string.