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Flutter Firebase get sum of elements from data

I have been able to group data from a field. However I want get the sum of element in a field for each group. But I can’t figure that out. Can anyone help me? Or is there a better approach to go this?
I need help, please. Thank you.

StreamBuilder(
        stream: FirebaseFirestore.instance
            .collectionGroup(widget.userRequestCollection)
            .where("Pay", isEqualTo: "Paid")
            .snapshots(),
        builder: (context, snapshot) {
          if (snapshot.connectionState == ConnectionState.waiting) {
            return const CircularProgressIndicator();
          } else if (snapshot.hasError) {
            return Text(widget.errorString);
          }

          if (snapshot.hasData) {
            return GroupedListView(
              elements: snapshot.data!.docs,
              groupBy: (element) => element['DepartureDate'],
              groupSeparatorBuilder: (String groupByValue) =>
                  Text(groupByValue),
              itemBuilder: (context, dynamic element) {
                double amount = element["AmountPaid"];
                 /*I want to get the sum of all the amount from each 
                 group but the '+=' is giving me error */
                double sum += amount;
                 return Text("$sum");
              },
              order: GroupedListOrder.ASC,
            );
            
          }
          return const Center(
            child: Text("No data"),
          );
        },
      )
Tags:

2

Answers


  1. 0

    If you want to use the (pretty new) sum operator for this, I have an example of how to use that in Flutter here. From that:

    final startAt = Timestamp.fromDate(DateTime(2024, 01, 03));
final endBefore = Timestamp.fromDate(DateTime(2024, 01, 04));
final aggregates = await col
  .where('timestamp', isGreaterThanOrEqualTo: startAt)
  .where('timestamp', isLessThan: endBefore)
  .aggregate(
    sum('latency'),
    average('latency'),
    count(),
  ).get();
print('''
  Logs on Jan 3:
    count=${aggregates.count}
    sum of latency=${aggregates.getSum("latency")}, 
    average latency=${aggregates.getAverage("latency")}
''');

    My data model is different from yours, but you should be able to similarly aggregate(sum('AmountPaid')) on the query, and then get the value with snapshot.getSum("AmountPaid").

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  2. 0

    how about this?

    StreamBuilder(
    stream: FirebaseFirestore.instance
        .collectionGroup(widget.userRequestCollection)
        .where("Pay", isEqualTo: "Paid")
        .snapshots(),
    builder: (context, snapshot) {
      if (snapshot.connectionState == ConnectionState.waiting) {
        return const CircularProgressIndicator();
      } else if (snapshot.hasError) {
        return Text(widget.errorString);
      }

      if (snapshot.hasData) {
        return GroupedListView(
          elements: snapshot.data!.docs,
          groupBy: (element) => element['DepartureDate'],
          groupSeparatorBuilder: (String groupByValue) =>
              Text(groupByValue),
          itemBuilder: (context, dynamic element) {
             // --- new code
             double sum = element
                .map((e) => e.data()['AmountPaid'])
                .reduce((value, element) => value + element);;
             // ---
             return Text("$sum");
          },
          order: GroupedListOrder.ASC,
        );
        
      }
      return const Center(
        child: Text("No data"),
      );
    },
  )
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