Django Aggregate- Division with Zero Values -

i using django's aggregate query expression total values. final value division expression may feature 0 denominator. need way escape if case, returns 0.

i've tried following, i've been using similar annotate expressions:

from django.db.models import sum, f, floatfield, case, when  def for_period(self, start_date, end_date):     return self.model.objects.filter(         date__range=(start_date, end_date)     ).aggregate(         sales=sum(f("value")),         purchase_cogs=sum(f('purchase_cogs')),         direct_cogs=sum(f("direct_cogs")),         profit=sum(f('profit'))     ).aggregate(         margin=case(             when(sales=0, then=0),             default=(sum(f('profit')) / sum(f('value')))*100         )     ) 

however, doesn't work, because error says:

'dict' object has no attribute 'aggregate'

what proper way handle this?

this not work; because aggregate returns dictionary, not queryset (see docs), can't chain 2 aggregate calls together.

i think using annotate solve issue. annotate identical aggregate, except in returns queryset results saved attributes rather return dictionary. result can chain annotate calls, or call annotate aggregate.

so believe like:

return self.model.objects.filter(     date__range=(start_date, end_date) ).annotate(  # call `annotate`     sales=sum(f("value")),     purchase_cogs=sum(f('purchase_cogs')),     direct_cogs=sum(f("direct_cogs")),     profit=sum(f('profit')) ).aggregate(  # `aggregate`     margin=case(         when(sales=0, then=0),         default=(sum(f('profit')) / sum(f('value')))*100     ) ) 

should work.

hope helps.