How to Update Field in Django Model Efficiently??

Let’s say you have the Django model defined as

class Book(models.Model):
    book_name = models.CharField(max_length=120)
    writen_by = models.ForeignKey(Author, on_delete=models.CASCADE, null=True)
    sale_count = models.PositiveIntegerField(blank=True, null=True)

There is a field “sale_count” that maintains the number of sales for the book.

Sometimes we need to perform a simple arithmetic operation on a field value, such as incrementing or decrementing the existing value. 

Here, in this example, we want to increase the sale of a book named “Learn Python” by one.

Here are a couple of ways to achieve the desired job.

Method 1: Obvious Way

Follow the steps below.

• Get the object of the model “Book” which has book name as “Learn Python”
• Update the field “sale_count” for then model “Book”.
• Save the object.

book = Book.objects.get(book_name='Learn Python')
book.sale_count += 1
book.save()

If the current value of the “sale_count” is 25, after executing the above lines of code, the updated value of the “sale_count” becomes 26 which will be saved in the database.

Here we are just updating the single field attribute, you update multiple fields as well.

Method 2: Using F Expression

You can also use the F expression to do the same job.

from django.db.models import F

book = Book.objects.get(book_name='Learn Python')
book.sale_count = F('sale_count') + 1
book.save()

Note: You have to import the F expression before using it.

Basically, these are the two methods you can use to update field in Django model.

Now the question is- which one you should use?

Which is more efficient to update the field in the Django model?

Using F expression is slightly faster by expressing the update relative to the original field value, rather than as an explicit assignment of a new value.

If you have any doubts, let’s discuss them in the comment section below.

Aniruddha Chaudhari

I am a Python enthusiast who loves Linux and Vim. I hold a Master of Computer Science degree from NIT Trichy and have 10 years of experience in the IT industry, focusing on the Software Development Lifecycle from Requirements Gathering, Design, Development to Deployment. I have worked at IBM, Ericsson, and NetApp, and I share my knowledge on CSEstack.org.