Opened 10 years ago

Last modified 10 years ago

#23581 closed Cleanup/optimization

Changing model field choices results in spurious migrations — at Version 2

Reported by: John-Scott Atlakson Owned by: nobody
Component: Migrations Version: 1.7
Severity: Release blocker Keywords:
Cc: Andrew Godwin, Iacopo Spalletti, Shai Berger Triage Stage: Accepted
Has patch: yes Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no

Description (last modified by John-Scott Atlakson)

Consider a simple model:

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?

Change History (2)

comment:1 by John-Scott Atlakson, 10 years ago

Description: modified (diff)

comment:2 by John-Scott Atlakson, 10 years ago

Description: modified (diff)
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