Django: Calculate the Sum of the column values through query

Question

I have a model

class ItemPrice( models.Model ):
     price = models.DecimalField ( max_digits = 8, decimal_places=2 )
     ....

I tried thi

Answer 1

You're probably looking for aggregate

from django.db.models import Sum

ItemPrice.objects.aggregate(Sum('price'))
# returns {'price__sum': 1000} for example

Answer 2

Using cProfile profiler, I find that in my development environment, it is more efficient (faster) to sum the values of a list than to aggregate using Sum(). eg:

sum_a = sum([item.column for item in queryset]) # Definitely takes more memory.
sum_b = queryset.aggregate(Sum('column')).get('column__sum') # Takes about 20% more time.

I tested this in different contexts and it seems like using aggregate takes always longer to produce the same result. Although I suspect there might be advantages memory-wise to use it instead of summing a list.

Answer 3

Annotate adds a field to results:

>> Order.objects.annotate(total_price=Sum('price'))
<QuerySet [<Order: L-555>, <Order: L-222>]>

>> orders.first().total_price
Decimal('340.00')

Aggregate returns a dict with asked result:

>> Order.objects.aggregate(total_price=Sum('price'))
{'total_price': Decimal('1260.00')}

Answer 4

Use .aggregate(Sum('column'))['column__sum'] reefer my example below

sum = Sale.objects.filter(type='Flour').aggregate(Sum('column'))['column__sum']