Django Count and Sum annotations interfere with each other

Question

While constructing a complexe QuerySet with several annotations, I ran into an issue that I could reproduce with the following simple setup.

Here are th

Answer 1

Based on the excellent answer from @rktavi, I created two helpers classes that simplify the Subquery/Count and Subquery/Sum patterns:

class SubqueryCount(Subquery):
    template = "(SELECT count(*) FROM (%(subquery)s) _count)"
    output_field = PositiveIntegerField()


class SubquerySum(Subquery):
    template = '(SELECT sum(_sum."%(column)s") FROM (%(subquery)s) _sum)'

    def __init__(self, queryset, column, output_field=None, **extra):
        if output_field is None:
            output_field = queryset.model._meta.get_field(column)
        super().__init__(queryset, output_field, column=column, **extra)

One can use these helpers like so:

from django.db.models import OuterRef

weapons = Weapon.objects.filter(unit__player_id=OuterRef('id'))
units = Unit.objects.filter(player_id=OuterRef('id'))

qs = Player.objects.annotate(weapon_count=SubqueryCount(weapons),
                             rarity_sum=SubquerySum(units, 'rarity'))