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 this to calculate the sum of price in this queryset:

items = ItemPrice.objects.all().annotate(Sum('price'))

What's wrong in this query? or is there any other way to calculate the Sum of price column?

I know this can be done by using for loop on queryset but i need an elegant solution.

Thanks!

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

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

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

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

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 5

Previous answers are pretty well, also, you may get that total with a line of vanilla code...

items = ItemPrice.objects.all()
total_price = sum(items.values_list('price', flat=True))

Answer 6

You could also get the sum this way:

def total_sale(self):
    total = Sale.objects.aggregate(TOTAL = Sum('amount'))['TOTAL']
    return total

Replace the 'amount' with the column name from your model you want to calculate the sum of and replace 'Sale' with your model name.

Answer 7

You need to use aggregate() and Sum() to calculate the sum of price column as shown below. *The query with all() is equivalent to the query without all() as shown below:

from django.db.models import Sum

print(ItemPrice.objects.all().aggregate(Sum('price')))
print(ItemPrice.objects.aggregate(Sum('price')))

Then, these dictionaries below are outputted on console:

{'price__sum': Decimal('150.00')}
{'price__sum': Decimal('150.00')}

And, you can change the default key price__sum to priceSum for price column as shown below:

from django.db.models import Sum
                                        # ↓ Here
print(ItemPrice.objects.all().aggregate(priceSum=Sum('price')))
print(ItemPrice.objects.aggregate(priceSum=Sum('price')))
                                  # ↑ Here

Then, the default key is changed as shown below:

{'priceSum': Decimal('150.00')}
{'priceSum': Decimal('150.00')}