auto_now vs auto_now_add in Django

The main difference between auto_now_add and auto_now is when they update the value of the field they are applied to.

auto_now_add is a field option for Django’s DateTimeField that automatically sets the field’s value to the current date and time whenever an object is created. It is used to track the creation time of an object.

auto_now is also a field option for Django’s DateTimeField that automatically sets the field’s value to the current date and time, but it updates the value whenever an object is saved (regardless of whether it is a new object or an existing one). It is used to track the last update time of an object.

Here’s an example of how you might use both options in a model:

from django.db import models

class BlogPost(models.Model):
    title = models.CharField(max_length=200)
    content = models.TextField()
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

In this example, the created_at field will be set to the current date and time whenever a new BlogPost object is created. The updated_at field, on the other hand, will be set to the current date and time whenever the object is saved (regardless of whether it’s a new object or an existing one).

So, the main difference between auto_now_add and auto_now is that auto_now_add is used to track the creation time of an object, while auto_now is used to track the last update time of an object.