Adding Sum of Object Attributes to Django Rest Framework Response - django

Question

I'm Trying to add the sum of multiple objects to a DRF response. For example, right now the response works with just listing the objects:
[
{
"id": "47d0deaa5c8c",
"amount": "25.00"
},
{
"id": "29787731",
"amount": "25.00"
}
]
But what I want is to be able to sum the amount attribute of those objects together and then include that in the response, so that it would look like this:
{
"sum":"50.00",
"objects":[
{
"id":"47d0deaa5c8c",
"amount":"25.00"
},
{
"id":"29787731",
"amount":"25.00"
}
]
}
Here's my current APIView:
class TransactionsList(GenericAPIView):
"""
Retrieve list of transactions
"""
authentication_classes = (TokenAuthentication,)
permission_classes = (IsAuthenticated,)
def get(self, request):
"""List Transactions"""
transaction = Transaction.objects.all()
serializer = TransactionSerializer(transaction, many=True)
return Response(serializer.data)
And Serializer:
class TransactionSerializer(serializers.ModelSerializer):
class Meta:
model = Transaction
fields = ('id', 'amount')
How could I efficiently go about adding the sum field into the response?

Answer 1

change
return Response(serializer.data)
to
from django.db.models import Sum
all_sum = transaction.aggregate(Sum('amount'))['amount__sum']
return Response({'sum': all_sum if all_sum else 0 , 'objects': serializer.data})

Answer 2

Since the amount field seems string type. So, we've to convert to int before summing them.
class TransactionsList(GenericAPIView):
"""
Retrieve list of transactions
"""
authentication_classes = (TokenAuthentication,)
permission_classes = (IsAuthenticated,)
def get(self, request):
"""List Transactions"""
transaction = Transaction.objects.all()
serializer = TransactionSerializer(transaction, many=True)
return_data = {"sum": str(sum([lambda items: int(items['amount'])])), "objects": serializer.data}
return Response(return_data)
If the amount field is int type, then you don't want to add do the type casting. If so, use this,
return_data = {"sum": sum([lambda items: items['amount']]), "objects": serializer.data}