在Django中结合〜Q和F？

Question

Query

Balance.objects.filter(~Q(fax_date=F('paused_date')))

returns empty qs even though I do have objects that fit the condition "fax date field not equal to paused date". Is it possible to use ~Q and F together like that?

ran a test like this:

        deals = Deal.objects.all()
        balance_pre = Balance.objects.filter(~Q(fax_date=F('paused_date')), fax_date__isnull=False, reserved=False)
        agr_nums = list(deals.filter(agr_name__isnull=False).values_list('agr_name', flat=True).distinct())
        agrs_with_fax = 0

        for agr_num in agr_nums:
            try:
                balance_agr = Balance.objects.get(number__icontains=agr_num)
                if balance_agr.fax_date is not None and balance_agr.fax_date != balance_agr.paused_date and not balance_agr.reserved:
                    agrs_with_fax += 1
            except Balance.DoesNotExist:
                pass
        agrs_with_fax2 = 0

        for agr_num in agr_nums:
            try:
                balance_pre.get(number__icontains=agr_num)
                agrs_with_fax2 += 1
            except Balance.DoesNotExist:
                pass

        r = [agrs_with_fax, agrs_with_fax2, balance_agr.fax_date, balance_agr.paused_date, balance_agr.reserved]

r returned is

[55, 0, datetime.date(2018, 7, 11), None, False]

I don't see my error, both cycles should return same result.

Answer 1

I created a Balance model in a fresh project just to test that print(qs.query) will show you the generated query(not in all cases) in this case. I used also exclude as @daniel-roseman suggested to prove that they were equivalent. I hope this help you.

>>> from django.db.models import F, Q
>>> qs = Balance.objects.filter(~Q(fax_date=F('paused_date')))
>>> print(qs.query)
SELECT "so_balance"."id", "so_balance"."fax_date", "so_balance"."paused_date" 
FROM "so_balance" WHERE NOT ("so_balance"."fax_date" = 
("so_balance"."paused_date"))
>>> qs = Balance.objects.exclude(fax_date=F('paused_date'))
>>> print(qs.query)
SELECT "so_balance"."id", "so_balance"."fax_date", "so_balance"."paused_date" 
FROM "so_balance" WHERE NOT ("so_balance"."fax_date" = 
("so_balance"."paused_date"))