Django migrate naive DateTimeField - django

Question

I am very sad: Every time I migrate the database, Django calls me naive:
$ python manage.py migrate
RuntimeWarning: DateTimeField Book.released received a naive datetime (2023-02-17 22:59:29.126480) while time zone support is active.
...and the worst part is: It's impossible to fix it!
Steps to reproduce:
$ python -V
Python 3.10.6
$ pipenv --version
pipenv, version 2022.11.11
$ mkdir naive-django
$ cd naive-django
$ pipenv install django
$ pipenv shell
$ python -m django --version
4.1.7
$ django-admin startproject naive_project
$ cd naive_project
$ python manage.py startapp naive_app
$ vim naive_project/settings.py
...
INSTALLED_APPS = [
'naive_app.apps.NaiveAppConfig',
...
$ vim naive_app/models.py
from django.db import models
class Book(models.Model):
title = models.CharField(max_length=100)
$ python manage.py makemigrations
$ python manage.py migrate
No problem so far. Let's add a DateTimeField now:
$ vim naive_app/models.py
from datetime import datetime
from django.db import models
class Book(models.Model):
title = models.CharField(max_length=100)
released = models.DateTimeField(default=datetime.now)
$ python manage.py makemigrations
$ python manage.py migrate
RuntimeWarning: DateTimeField Book.released received a naive datetime (2023-02-17 22:59:29.126480) while time zone support is active.
Oh no! I made a terrible mistake! If only it was not impossible to fix it... Let's try anyway:
$ vim naive_app/models.py
from django.utils import timezone # timezone instead of datetime
from django.db import models
class Book(models.Model):
title = models.CharField(max_length=100)
released = models.DateTimeField(default=timezone.now) # timezone instead of datetime
$ python manage.py makemigrations
$ python manage.py migrate
Hey! It worked! It was not impossible after all!
Let's write a test:
$ vim naive_app/tests.py
from django.test import TestCase
class NaiveTests(TestCase):
def test_naive(self):
pass
$ python manage.py test
RuntimeWarning: DateTimeField Book.released received a naive datetime (2023-02-17 23:10:54.367162) while time zone support is active.
Oh no! It's not fixed! Every time I run the tests, a database is built from scratch and my old migration is executed!
$ echo "Please Mister Django, I apologize. I'm going to delete my model."
$ vim naive_app/models.py
# from django.utils import timezone # timezone instead of datetime
# from django.db import models
#
#
# class Book(models.Model):
# title = models.CharField(max_length=100)
# released = models.DateTimeField(default=timezone.now) # timezone instead of datetime
$ python manage.py makemigrations
$ python manage.py migrate
$ python manage.py test
RuntimeWarning: DateTimeField Book.released received a naive datetime (2023-02-17 23:18:36.955394) while time zone support is active.
I still get a warning while the model is deleted and the test is almost empty.
Would you have an idea?
$ exit
$ pipenv --rm
$ cd ..
$ rm -rf naive-django

Answer 1

If you squash the two migrations that add the DateTimeField and fix the default they will be optimised into a single migration that uses the latest default, the old operation using the incorrect default will then not run so you shouldn't get the warning
$ python manage.py squashmigrations naive_app 0002 0003
$ python manage.py migrate
$ python manage.py test