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
28056	Reverse migration for model rename with cross-app ForeignKey fails	Paul Tiplady	Bhuvnesh	"When attempting to reverse a migration for the rename of a model, where the model has ForeignKey references to it from models in other apps, the reverse migration fails with the following error:

`ValueError: The field <foreignkey_field> was declared with a lazy reference to '<old_model_name>', but app 'one' doesn't provide model '<old_model_name>'`

I've put a simple repro up on github here: https://github.com/paultiplady/django-migration-bug, but here's an outline of the problem:

With two apps, `one` and `two`, and the models:

one/models.py:
{{{
from django.db import models


class Rename1(models.Model):
    pass
}}}

two/models.py:
{{{
from django.db import models


class Related2(models.Model):
    rename1 = models.ForeignKey('one.Rename1')
}}}

Renaming Rename1 to Rename2 produces a simple migration:

0002_auto_20170408_1617.py:
{{{
class Migration(migrations.Migration):

    dependencies = [
        ('one', '0001_initial'),
    ]

    operations = [
        migrations.RenameModel(
            old_name='Rename1',
            new_name='Rename2',
        ),
    ]
}}}

But when this migration is reversed, the error is raised:

`ValueError: The field two.Related2.rename1 was declared with a lazy reference to 'one.rename1', but app 'one' doesn't provide model 'rename1'.`

It's unclear from the error message how I'd even go about attempting to address this problem, and the docs don't mention anything about handling this case (as far as I can tell).

Expected behaviour is to be able to handle this reverse-rename seamlessly, or at least provide a sensible error message if this operation is unsupported.

Naively it looks like the problem is that the `two.Related2` model has not been given its own migration when its ForeignKey was changed from `one.Rename1` to `one.Rename2`, instead that change is tracked implicitly and incorrectly in the RenameModel step."	Bug	closed	Migrations	1.10	Normal	duplicate		Friedrich Delgado	Accepted	1	0	0	1	0	0