Summation of Django Queryset

Django Queryset is a powerful database API that provides an abstraction layer for interacting with relational databases. It allows us to perform complex filtering, aggregation, and ordering on our data.

One important operation we may need to perform on a Queryset is the summation of a particular field. In this article, we will explore how to achieve this by using Django's aggregation functions.

Aggregation Functions

Django provides us with several aggregation functions that we can use to perform calculations on our Querysets. Some of these functions include:

• Sum: calculates the sum of a field
• Avg: calculates the average of a field
• Min: gets the minimum value of a field
• Max: gets the maximum value of a field
• Count: gets the number of records in a Queryset

For this article, we will focus on the Sum function.

Usage

Suppose we have a Book model that has a price field. We can calculate the total cost of all books by using the Sum function as follows:

from django.db.models import Sum
from myapp.models import Book

total_cost = Book.objects.all().aggregate(Sum('price'))['price__sum']

Here, we use the aggregate method to apply the Sum function on the price field. The result is stored in a dictionary-like object, which we can access using the ['price__sum'] key.

Conclusion

In this article, we have seen how to use the Sum function in Django Queryset to calculate the total cost of all books in our Book model. This is just one example of what can be achieved with Django's aggregation functions. We encourage you to explore other aggregation functions to see what you can do with them.