Flutter - Map function inside Future method - flutter

Question

How can I run a map function inside a Future method?
This is my code:
Future deactivateLogs(List<String> members) async {
return members.map((member) async {
return await logDataCollection
.document('log-$member')
.updateData({
'active': false,
});
});
}
When I call this method, the map function is not being executed. How can I change the syntax so that it runs?
The goal is that the data is being updated in the database (backend) for each of the individual 'member' strings.
The problem can also be made easier:
Future deactivateTribeLogs() {
List<int> list = [1, 2, 3];
list.map((e) => print(e));}
The map function does not run in this case either.
Many thanks in advance!

Answer 1

You have two problems:
You're using an asynchronous callback with Iterable.map, but nothing will wait for the callbacks to complete.
Iterable.map is lazy; if you never attempt to use the result of a callback, it won't bother executing that callback at all. (Iterable.map normally is meant for functional-style programming where the callbacks are "pure"; you usually don't want to use it with callbacks that have side-effects.)
When you call Iterable.map with an asynchronous callback, it returns an iterable of Futures. If you don't care about execution order of callbacks, you could use Future.wait on that directly:
Future<void> deactivateLogs(List<String> members) async {
var waitList = members.map((member) async {
return await logDataCollection.document('log-$member').updateData({
'active': false,
});
});
await Future.wait(waitList);
}
Doing so also will evaluate all elements of the returned list of Futures and will avoid your issue with Iterable.map's lazy evaluation.

Answer 2

You can also use for loop for that :
Future deactivateLogs(List<String> members) async {
for(var i = 0; i< members.length; i++) {
await logDataCollection
.document('log-' + members[i])
.updateData({
'active': false,
});
}
return ;
}

Answer 3

If you look at the definition of List::map, you will see that it returns an Iterable, which is not evaluated.
Another way of saying it is that List::map is lazy and will not run until the iterable is either explicitly iterated or converted to a list.
Actually from the documentation, it says:
Returns a new lazy Iterable with elements that are created by calling f on each element of this Iterable in iteration order.
To fix your problem, just append .toList() at the end of the .map call, and it will force the iterable to be evaluated.
Since you are not looking to return anything from the function, you can just use Future::forEach:
Future<void> deactivateLogs(List<String> members) =>
Future.forEach(members, (member) => logDataCollection
.document('log-$member')
.updateData({
'active': false,
});
);
Full example
void main() async {
print('start');
await deactivateLogs(["Foo", "Bar", "Hello", "World"]);
print('end');
}
Future<void> deactivateLogs(List<String> members) =>
Future.forEach(members, (member) {
final v = await Future(() => member);
print(v);
});
Output
start
Foo
Bar
Hello
World
end