Django 1.11 Annotating a Subquery Aggregate

Question

This is a bleeding-edge feature that I\'m currently skewered upon and quickly bleeding out. I want to annotate a subquery-aggregate onto an existing queryset. Doing this bef

Answer 1

If I understand correctly, you are trying to count Spaces available in a Carpark. Subquery seems overkill for this, the good old annotate alone should do the trick:

Carpark.objects.annotate(Count('spaces'))

This will include a spaces__count value in your results.

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OK, I have seen your note...

I was also able to run your same query with other models I had at hand. The results are the same, so the query in your example seems to be OK (tested with Django 1.11b1):

activities = Activity.objects.filter(event=OuterRef('pk')).values('event')
count_activities = activities.annotate(c=Count('*')).values('c')
Event.objects.annotate(spaces__count=Subquery(count_activities))

Maybe your "simplest real-world example" is too simple... can you share the models or other information?