id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
23581	Changing model field choices results in spurious migrations	John-Scott Atlakson	nobody	"Consider a simple model:

{{{#!python
from django.db import models

CHOICES = (
    ('1', '1'),
)

class BasicModel(models.Model):
    choices = models.CharField(choices=CHOICES, max_length=100)
}}}

If CHOICES is changed e.g. CHOICES += (('2', '2'),), then `makemigrations` insists on creating a new migration for this change. However, the migration appears to mostly be a no-op. `sqlmigrate` on PostgreSQL shows:
{{{
BEGIN;
ALTER TABLE ""core_basicmodel"" ALTER COLUMN ""choices"" DROP DEFAULT;

COMMIT;
}}}

Which is slightly strange since the initial migration never set a DEFAULT, so there is nothing to DROP.
 
I first noticed this working with django-cms (see https://github.com/divio/django-cms/issues/3479). In some cases when I attempt to make a migration for an unrelated app, `makemigrations` will forcefully create a migration for the `cms` app because the settings.CMS_TEMPLATES choices have changed. It then makes this automatically created migration (which is output in the virtualenv e.g. `env/src/django-cms/cms/migrations_django`) a dependency for the migration I actually intended to create. There doesn't appear to be a way to avoid this. This means I now have a migration I actually need for one of my apps that is completely dependent on me creating a migration for a third party app, which I don't directly control, resulting in migrations that are broken for other developers. 

This can also happen when the choices differ in development vs deployment, Django will complain:
{{{
  Your models have changes that are not yet reflected in a migration, and so won't be applied.
  Run 'manage.py makemigrations' to make new migrations, and then re-run 'manage.py migrate' to apply them.
}}}
I am not familiar with the migration internals, but since 'choices' isn't used (at least not on PostgreSQL) to make any actual alterations to the database shouldn't it ignore this attribute?"	Uncategorized	new	Migrations	1.7	Normal				Unreviewed	0	0	0	0	0	0