Django exclude one object cause more to be excluded - django

Question

that's the weirdest bug I've ever faced since I started using Django
I've a queryset with some corrupt data that needs to be excluded, when printing the queryset length it prints 97 and when prints the corruptdata queryset it's 2 so the result must be 95, but what I get is only 70!!
here's my code
qs = model.objects.filter(
query,
**sku_filter
).values(
'sku',
'sku__asin',
'sku__title',
).order_by(
'-report_date',
'sku',
).annotate(
in_inbound=Coalesce(
LedgerQuery.in_inbound_subquery,
Value(0)
)
).annotate(
fnsku=F('fnsku'),
action=F('sku__reconciliation_activity__action'),
case_number=F('sku__reconciliation_activity__case_number'),
is_being_manually_reconciled=F('sku__reconciliation_activity__is_being_manually_reconciled'),
missing_subquery_count = Count(missing_subquery_count),
missing=Subquery(
queryset=missing_subquery
),
available=Sum(
'ending_warehouse_balance',
filter=Q(disposition='SELLABLE')
),
total_units=Sum(
F('ending_warehouse_balance') + # Available + Unsellable units in all the countries warehouses
Abs('in_transit_between_warehouses') + # Reserved Component 1
Abs('customer_shipments') # Reserved Component 2
) + F('missing') + F('in_inbound'),
# it's important to put out the missing from the Sum, otherwise
# the result will be missing * grouped by rows
main_image_link=Subquery(
queryset=main_image_link_subquery
)
).filter(
# this is a hacky way to exclude "corrupt" data
~Q(total_units=0),
~Q(
Q(action='NEEDED') | Q(action='TICKET'),
missing=0
),
)
##prints 97
print(qs.count())
##prints 70
print("c1", qs.filter(
~Q(
action=ReconciliationActivity.ActionChoices.NO_ACTION, missing__gte=1
)
).count()
)
##prints 2
print(
qs.filter(
action=ReconciliationActivity.ActionChoices.NO_ACTION, missing__gte=1
).count()
)
I tried to convert it to sql to be easier for debug but it was more then 45k of words and eventually I couldn't find anything wrong with it
and no it's not because of the q filter, I tried to print objects with only missing gte 1 or has no action and found a lot

Answer 1

The issue is with the 2nd query in which you get count of 70. Negation on the query set with multiple parameters doesn't work the way you think.
To make this easier to understand, let me briefly explain De Morgan's Law that is in effect here.
not (A and B) = not (A) or not (B)
In your 2nd query, the count that you get includes all the objects that either don't have ReconciliationActivity.ActionChoices.NO_ACTION or their missing__get is not 1. If any case is true, then object contributes to the count value.
The correct query that you should write is:
##prints 95
print("c1", qs.filter(
~Q(
action=ReconciliationActivity.ActionChoices.NO_ACTION
) &
~Q(
missing__gte=1
)
)
).count()
)
And P.S. this is not a bug. This is how conditions work everywhere.