#23581: Changing model field choices results in spurious migrations
-------------------------------+--------------------
Reporter: john_scott | Owner: nobody
Type: Uncategorized | Status: new
Component: Migrations | Version: 1.7
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------+--------------------
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 a dependency for the
migration I actually intended to create. There doesn't appear to be a way
to avoid this.
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.
}}}
So far this seems to mostly be harmless if slightly confusing/annoying. 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?
--
Ticket URL: <https://code.djangoproject.com/ticket/23581>
Django <https://code.djangoproject.com/>
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