Firestore calculate values from documents - firebase

Question

I have created a Future which prints out all of the fields from my firestore collection 'products' documents, but this collection is one of many of the same name, as seen below, and therefore I am printing out all of the values of each of the collections documents' fields. I want to add the 'productPrice' for each document that is in it's own collection 'products'
First Products Collection:
Second Products Collection:
My function is listening to all of the 'products' collections. When I try to print the productPrice field values for each of their documents, I get them all printed out, as seen below in the console. I need to add the productPrice values of 29.33 + 39.69 together to make
69.02 but I don't know how to do that without also adding the unrelated document that has the value of 149.99
final FirebaseAuth _auth = FirebaseAuth.instance;
final FirebaseFirestore _cloudStore = FirebaseFirestore.instance;
List<OrderModel> orders = [];
List<ProductModel> orderProductList = [];
Future startListening() async {
User currentUser = _auth.currentUser;
if(currentUser != null){
_cloudStore
.collection("orders")
.doc(currentUser.email)
.collection("orders")
.snapshots()
.listen((event) {
orders = event.docs.map((value){
return OrderModel(
value.data()["name"],
value.data()["date"],
value.data()["dateTime"],
value.data()["status"],
value.data()["productImage"],
);
}).toList();
for(var i = 0; i < orders.length; i++){
if(currentUser != null){
_cloudStore
.collection("orders")
.doc(currentUser.email)
.collection("orders")
.doc(orders[i].dateTime)
.collection("products")
.snapshots()
.listen((event){
orderProductList = event.docs.map((value){
return ProductModel(
value.data()['productName'],
value.data()['productQuantity'],
value.data()['productPrice'],
value.data()['productImage'],
);
}).toList();
print('separate');
event.docs.forEach((value){
var prices = value.data()['productPrice'];
print(prices);
});
notifyListeners();
});
}
}
notifyListeners();
});
} else {
return null;
}
}
My current output in the console:
Restarted application in 881ms.
Reloaded 0 of 983 libraries in 32ms.
flutter: separate
flutter: 149.99
flutter: separate
flutter: 29.33
flutter: 39.69

Answer 1

If I understand the question correctly, It should work if you change your code like that:
double sum = 0.0;
event.docs.forEach((value){
var prices = value.data()['productPrice'];
sum = sum + prices;
print(prices);
});
print(sum);
You can just add that after your print('separate'); statement.