How to Use Aggregate in Django: Syntax and Examples

In Django, use the aggregate() method on a queryset to perform calculations like sum, average, count, min, and max. You pass aggregation functions such as Sum() or Count() inside aggregate() to get the result as a dictionary.

Syntax

The aggregate() method is called on a Django queryset and takes one or more aggregation functions as keyword arguments. Each argument names the result key and uses an aggregation function like Sum(), Count(), Avg(), Min(), or Max() applied to a model field.

• queryset.aggregate(result_name=AggregationFunction('field_name'))
• result_name: the key for the returned dictionary
• AggregationFunction: one of Django's aggregation functions
• 'field_name': the model field to aggregate

python

from django.db.models import Sum, Count, Avg, Min, Max

# Example syntax
result = MyModel.objects.aggregate(
    total=Sum('field_name'),
    count=Count('field_name'),
    average=Avg('field_name'),
    minimum=Min('field_name'),
    maximum=Max('field_name')
)

Example

This example shows how to calculate the total price and average price of all products in a Product model using aggregate(). The result is a dictionary with keys total_price and average_price.

python

from django.db import models
from django.db.models import Sum, Avg

class Product(models.Model):
    name = models.CharField(max_length=100)
    price = models.DecimalField(max_digits=8, decimal_places=2)

# Calculate total and average price
result = Product.objects.aggregate(
    total_price=Sum('price'),
    average_price=Avg('price')
)
print(result)

Output

{'total_price': Decimal('12345.67'), 'average_price': Decimal('123.46')}

Common Pitfalls

Common mistakes when using aggregate() include:

• Calling aggregate() without parentheses on the queryset (it must be called as a method).
• Using aggregation functions without importing them from django.db.models.
• Expecting aggregate() to return a queryset instead of a dictionary.
• Trying to chain aggregate() with other queryset filters after calling it (it returns a dictionary, so chaining fails).

python

from django.db.models import Sum

# Wrong: forgetting parentheses
# result = Product.objects.aggregate

# Wrong: no import of Sum
# result = Product.objects.aggregate(total=Sum('price'))

# Correct usage
result = Product.objects.aggregate(total=Sum('price'))
print(result)

Output

{'total': Decimal('12345.67')}

Quick Reference

Aggregation Function	Description	Example Usage
Sum	Calculates the sum of a field	aggregate(total=Sum('field_name'))
Count	Counts the number of non-null values	aggregate(count=Count('field_name'))
Avg	Calculates the average value	aggregate(avg=Avg('field_name'))
Min	Finds the minimum value	aggregate(min=Min('field_name'))
Max	Finds the maximum value	aggregate(max=Max('field_name'))

Key Takeaways

Use aggregate() on a queryset with aggregation functions to get summary data as a dictionary.

Always import aggregation functions like Sum and Count from django.db.models.

aggregate() returns a dictionary, not a queryset, so you cannot chain it further.

Aggregation functions work on model fields and return results keyed by the names you provide.

Common functions include Sum, Count, Avg, Min, and Max.