[Django]-Difference between auto_now and auto_now_add

by

65👍

✅

auto_now takes precedence (obviously, because it updates field each time, while auto_now_add updates on creation only). Here is the code for DateField.pre_save method:

def pre_save(self, model_instance, add):
    if self.auto_now or (self.auto_now_add and add):
        value = datetime.date.today()
        setattr(model_instance, self.attname, value)
        return value
    else:
        return super().pre_save(model_instance, add)

As you can see, if auto_now is set or both auto_now_add is set and the object is new, the field will receive current day.

The same for DateTimeField.pre_save:

def pre_save(self, model_instance, add):
    if self.auto_now or (self.auto_now_add and add):
        value = timezone.now()
        setattr(model_instance, self.attname, value)
        return value
    else:
        return super().pre_save(model_instance, add)
👤awesoon

10👍

According to the django documentation using both auto_now and auto_now_add in your model fields as True will result in an error because they are both mutually exclusive.

👤Oladapo Oluwaseyi Bolarinwa

10👍

These fields are built into Django for expressly this purpose — auto_now fields are updated to the current timestamp every time an object is saved and are therefore perfect for tracking when an object was last modified, while an auto_now_add field is saved as the current timestamp when a row is first added to the database and is therefore perfect for tracking when it was created.

👤Alphonse Prakash

6👍

As Official Django documentation says –

auto_now, auto_now_add and default are mutually exclusive and will result in an error if used together

👤Harshit Gangwar

1👍

If a filed in a model contains both the auto_now and auto_now_add set to True will result in an error like this:

ERRORS:
appname.Model.field_name: (fields.Efield_number) The options auto_now, auto_now_add, and default are mutually exclusive. Only one of these options may be present.

👤Md Moksedul Alam

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