[Answered ]-Annotate Django Foreign Key model instance

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1👍

Is there a way with a single query without the loop?

Not at the time of writing. You could use a Prefetch object, but that would result in two queries then.

But likely the for loop is not much of a problem: the data is already there, so the loop itself will likely take a few microseconds.

What you however forgot (likely only in your example) is to .select_related('base_model'), so:

from django.db.models import Count

foos = Foo.objects.select_related('base_model').annotate(
    base_model_bars_count=Count('base_model__bars')
)
for foo in foos:
    foo.base_model.bars_count = foo.base_model_bars_count

I agree that it is not very convenient, but performance-wise, the loop will likely not matter much, given you do this after slicing/pagination.

👤willeM_ Van Onsem

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