Django: annotate Sum Case When depending on the status of a field

Question

In my application i need to get all transactions per day for the last 30 days.

In transactions model i have a currency field and i want to convert the value in euro if

Answer 1

The only thing that remains is an order_by. This will (yeah, I know that sounds strange), force Django to perform a GROUP BY. So it should be rewritten to:

queryset = Transaction.objects.filter(
    created__gte=last_month,
    status=Transaction.COMPLETED
).extra(
    {"date": "date_trunc('day', created)"}
).values(
    'date'
).annotate(
    amount=Sum(Case(
        When(currency=Core.CURRENCY_EUR, then='amount'), 
        When(currency=Core.CURRENCY_USD, then=F('amount') * 0.8662), 
        When(currency=Core.CURRENCY_GBP, then=F('amount') * 1.1413),
        default=0,
        output_field=FloatField()
    ))
).order_by('date')

(I here fixed the formatting a bit to make it more readable, especially for small screens, but it is (if we ignore spacing) the same as in the question, except for .order_by(..) of course.)

Answer 2

We need to aggregate the query set to accomplish what you are trying.

Try using aggregate()

queryset = Transaction.objects.filter(created__gte=last_month, status=Transaction.COMPLETED).extra({"date": "date_trunc('day', created)"}).values('date').aggregate(
amount=Sum(Case(When(currency=Core.CURRENCY_EUR, then='amount'), 
                When(currency=Core.CURRENCY_USD, then=F('amount') * 0.8662), 
                When(currency=Core.CURRENCY_GBP, then=F('amount') * 1.1413), default=0, output_field=FloatField())))

for more info: aggregate()