django aggregate or annotate

Thank you all very much. The problem I was having is documented in the last version, it is about the annotate and filter precedence.

areas = Area.objects.filter(event__in = eventQuery).annotate(num=Count('event'))

My error was in the fact that I was doing annotate first and filter second.

for a given area:

my_area = Area.objects.all()[0]
Event.objects.filter(area=my_area).count()

annotation

events = Event.objects.annotate(Count('area'))
for event in events:
    print event, event.area__count

events = Event.objects.annotate(count=Count('area'))
for event in events:
    print event, event.count

See the following docs:

https://docs.djangoproject.com/en/dev/ref/models/querysets/#annotate

If you just need the total number of events for a single area, you don't need either annotate or aggregate, a simple count will do:

Event.objects.filter(area=my_area).count()

If you want the count of events for multiple areas, you need annotate in conjunction with values:

Event.objects.values('area').annotate(Count('area'))

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