#28056: Reverse migration for model rename with cross-app ForeignKey fails
----------------------------------------+------------------------
Reporter: Paul Tiplady | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: 1.10
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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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.
--
Ticket URL: <https://code.djangoproject.com/ticket/28056>
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