How to fetch data and update it from firebase - flutter

Question

I am having trouble trying to fetch data from firebase and updating the values from it.
I have a restaurant name and the number of times it has been picked (user chooses to go to that restaurant to eat). I am trying to retrieve the numPicked and update it by adding one if the user decides to go there again.
Here i am trying to fetch ONE specific document and trying to store the docID and the variables I need to update.
docID = doc.id; docID is return NULL
meaning that the foreach loop isn't even being read.
Future<bool> searchQuery(
{required String restaurantName,
required var userID,
required db}) async {
int addOne = 1; //addes one if it has been picked
//this is not working
try {
Query query2 =
db.where('userId', isEqualTo: FirebaseAuth.instance.currentUser!.uid);
Query query = query2.where('restaurantName', isEqualTo: restaurantName);
await query.get().then((querySnapshot) {
// ignore: avoid_function_literals_in_foreach_calls
querySnapshot.docs.forEach((doc) {
docID = doc.id;
numPicked = doc['numPicked'];
restaurantExist = true;
});
}).catchError((error) {
// print('error querying: #error');
});
} catch (ex) {
// ignore: avoid_print
print(ex);
}
//this is not working
int totalPicked = numPicked + addOne;
//if the restaurant exist then update the numpicked for that specific restaurant
if (restaurantExist) {
try {
var query = db
//.collection('NumRestaurantPicked')
.doc(docID);
await query.update({'numPicked': totalPicked.toString()});
} catch (ex) {}
}
return restaurantExist;
}

Answer 1

The docID and numPicked variables are not defined in the method signature, so they are not accessible outside of the try block. They should be defined as class variables, so they can be accessed from other methods.