#26149: Invalid migration generated when using order_with_respect_to and a
unique_together constraint
----------------------------+--------------------
Reporter: richardxia | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: 1.9
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
----------------------------+--------------------
I ran into a bug when trying to generate and apply a migration for a model
that has the `order_with_respect_to` option set along with a
`unique_together` which involves the implicit `_order` field created by
`order_with_respect_to`. For example, if you have the following models:
{{{#!python
class Bar(models.Model):
pass
class Foo(models.Model):
class Meta:
order_with_respect_to = 'bar'
unique_together = ('bar', '_order')
bar = models.ForeignKey(Bar)
}}}
when you generate the migrations with `make_migrations`, it creates a
migration with the operations out of order. It attempts to run the
`AlterUniqueTogether` operation before the `AlterOrderWithRespectTo`,
which is problematic because the implicit `_order` field is created by the
latter operation but the former operation tries to create a uniqueness
constraint using it. This results in the error:
`django.core.exceptions.FieldDoesNotExist: Foo has no field named
u'_order'`
For convenience, I've created a Github repo that sets up the models, so
that to reproduce the bug, all you have to do is run `makemigrations`
followed by `migrate`: https://github.com/richardxia/django-migration-bug
--
Ticket URL: <https://code.djangoproject.com/ticket/26149>
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