Django 将正值与负值分开

Question

Can you sum positive values separately from negative values?

I have a table that looks like this:

class Order(models.Model):
    date = models.DateField()
    amount = models.DecimalField()

I'm looking to get a queryset that sums the postive amounts seperate from the negative amounts and groups by week:

Year
Week
Sum of positive amounts
Sum of negative amounts

I'm able to get all positive amounts per week seperately by doing:

Order.objects.filter(amount__gt=0).annotate(year_week=Trunc('date', 'week', output_field=DateField())).\
annotate(year=ExtractYear('year_week')).annotate(week=ExtractWeek('year_week')).\
values("year_week", "year", "week").annotate(value=Sum("amount")).order_by("-year_week")

I can do this again for the negative value, but then I have two seperate querysets. Can I merge them efficiently without looping manually or is there a way to do both in a single query?

Answer 1

Yes, since django-2.0 , most aggregate functions have afilter=… parameter [Django-doc] :

from django.db.models import Q, Sum
from django.db.models.functions import ExtractYear, ExtractWeek

Order.objects.values(
    year=ExtractYear('date'),
    week=ExtractWeek('date')
).annotate(
    sum_pos=Sum('amount'),
    sum_neg=Sum('amount')
).order_by('year', 'week')