Sum Product using Django ORM

Question

I need to calculate the sumproduct of two fields from Django queryset.

I have checked the answer in Django Aggregation: Summation of Multiplication of two fields but it doesnt work. They suggest the following code for django < 1.8:

from django.db.models import Sum
MyModel.objects.filter(<filters>).aggregate(Sum('field1', field="field1*field2"))

which returns the sum of the 'field1' not the defined field="field1*field2"

and for django >= 1.8

from django.db.models import Sum, F
MyModel.objects.filter(<filters>).aggregate(Sum(F('field1')*F('field2')))

which returns TypeError: Complex aggregates require an alias

@MohammadUmair My Django version is 2.1.2 and I checked the second code in the link which was suggested to use for django >= 1.8 but it did not work as well — Mike, Feb 07 '19 at 10:31
from django.db.models import Sum, F MyModel.objects.filter().aggregate(Sum(F('field1')*F('field2'))) — Mike, Feb 07 '19 at 10:31
I get the error "Complex aggregates require an alias" on this one — Mike, Feb 07 '19 at 10:32

score 4 · Accepted Answer · answered Feb 07 '19 at 10:32

4

Try something like this

from django.db.models import Sum, F
MyModel.objects.filter(<filters>).aggregate(sum=Sum(F('field1')*F('field2')))["sum"]

answered Feb 07 '19 at 10:32

Umair Mohammad

Tried it right now. I get the FieldError: Expression contains mixed types. You must set output_field. – Mike Feb 07 '19 at 10:35
1

Thanks it worked. I searched this error and resolved it through https://stackoverflow.com/questions/38546108/django-aggregation-expression-contains-mixed-types-you-must-set-output-field – Mike Feb 07 '19 at 10:40

1 Answers1