custom function in FlutterFlow: cant return int value of firestore document

Question

Im trying to sum an integer field in my firestore document collection, although I keep gettings errors. It looks like because firestore store integers as "num".

A value of type 'Future' can't be returned from the function 'calculateTotalItemQty' because it has a return type of 'int'.

import 'dart:convert';
import 'dart:math' as math;

import 'package:flutter/material.dart';
import 'package:google_fonts/google_fonts.dart';
import 'package:intl/intl.dart';
import 'package:timeago/timeago.dart' as timeago;
import '/flutter_flow/lat_lng.dart';
import '/flutter_flow/place.dart';
import '/flutter_flow/uploaded_file.dart';
import '/flutter_flow/custom_functions.dart';
import '/backend/backend.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import '/backend/schema/structs/index.dart';
import '/auth/firebase_auth/auth_util.dart';

int calculateTotalItemQty(
  String? itemId,
  String? businessId,
) {
  /// MODIFY CODE ONLY BELOW THIS LINE

  // sum value of all itemQty in purchaseLine where itemId is itemId and businessId is businessId
  return FirebaseFirestore.instance
      .collection('purchases')
      .where('itemId', isEqualTo: itemId)
      .where('businessId', isEqualTo: businessId)
      .get()
      .then((querySnapshot) {
    int totalQty = 0;
    querySnapshot.docs.forEach((doc) {
      int value = doc['itemQty'];
      totalQty += value.toInt();
    });
    return totalQty;
  }).catchError((error) {
    print('Error getting total item qty: $error');
    return null;
  });

  /// MODIFY CODE ONLY ABOVE THIS LINE
}

Tried to use .toInt() but still not working

Answer 1

As others mentioned, you can make your function async and return a Future.

However, in FlutterFlow's custom code section, "Custom Actions" can return a Future and not "Custom Function". So you can move the code under a Custom Action snippet and it should work.

You can call that custom action in your Action Flow Editor where you can get that return int value and then do whatever you want with it.

Answer 2

You need to add await keyword in front of Firebase method. Like below code

Future<int?> calculateTotalItemQty(
  String? itemId,
  String? businessId,
) async {   
  return await FirebaseFirestore.instance
      .collection('purchases')
      .where('itemId', isEqualTo: itemId)
      .where('businessId', isEqualTo: businessId)
      .get()
      .then((querySnapshot) {
    int totalQty = 0;
    querySnapshot.docs.forEach((doc) {
      int value = doc['itemQty'];
      totalQty += value.toInt();
    });
    return totalQty;
  }).catchError((error) {
    print('Error getting total item qty: $error');
    return null;
  });
}

Answer 3

The problem is that your function is attempting to return a Future<int> instead of just an int. To resolve this, make your function async and utilize the await keyword for the Firestore query.

Future<int> calculateTotalItemQty(
  String? itemId,
  String? businessId,
) async {
  try {
   /// MODIFY CODE ONLY BELOW THIS LINE

  // sum value of all itemQty in purchaseLine where itemId is itemId and businessId is businessId
    QuerySnapshot querySnapshot = await FirebaseFirestore.instance
        .collection('purchases')
        .where('itemId', isEqualTo: itemId)
        .where('businessId', isEqualTo: businessId)
        .get();

    int totalQty = 0;
    querySnapshot.docs.forEach((doc) {
      int value = doc['itemQty'] as int;
      totalQty += value;
    });

    return totalQty;
  } catch (error) {
    print('Error getting total item qty: $error');
    return 0;
  }
  
  
  /// MODIFY CODE ONLY ABOVE THIS LINE
}

I hope this helps.