Django datetime default value in migrations

Question

I've read some questions about this issue in so, also this question is not giving the correct answer for my case:

I'm adding a created_time field in my already existing models, so no date in the mysql table belonging to the model.

class Configs(models.Model):
    ...
    creation_date = models.DateTimeField(auto_now_add=True, blank=True)
    ...

I apply the migration using python manage.py makemigrations

And I get this error:

You are trying to add a non-nullable field 'creation_date' to collections without a default; we can't do that (the database needs something to populate existing rows). Please select a fix:

I tryed many options:

creation_date = models.DateTimeField(auto_now_add=True)

This one is giving the same error.

How can this migration be achieved, if USE_TZ in settings is set to False?
Btw, is this a bug in Django 1.9.4 makemigrations script?

Answer 1

auto_now_add set the current datetime when the instance is created, which never happens during your migration so you are trying to leave NULL a non-nullable field.

The solution would be to add a default date to your model, makemigrations, then remove the default parameter from the model, makemigrations again and finally migrate. You can achieve the same adding null=True to the field, adding a RunPython or RunSQL to your migration that populates the field, and then remove the null=true from the field.

At the end you can merge both migration files (or simple write it yourself) to end with something like:

operations = [
    migrations.AddField(
        model_name='configs',
        name='creation_date',
        field=models.DateTimeField(auto_now_add=True, null=True, blank=True),
    ),
   migrations.RunPython(populate_dates),
   migrations.AlterField(
        model_name='configs',
        name='creation_date',
        field=models.DateTimeField(auto_now_add=True, blank=True),
    ),
]

I just wrote it so I hope it does not have many typos