#28916: Changing the type of a ForeignKey and changing unique_together creates
migrations in the wrong order, causing migrations to fail
----------------------------+--------------------------------------
Reporter: fredley | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: 2.0
Severity: Normal | Resolution:
Keywords: migrations | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
----------------------------+--------------------------------------
Description changed by fredley:
Old description:
> models.py before:
>
> {{{
> class MyModel(models.Model):
> fka = models.ForeignKey(SomethingA, ...)
> date = models.DateField()
>
> class Meta:
> unique_together = ('fka', 'date')
> }}}
>
> models.py after:
>
> {{{
> class MyModel(models.Model):
> fkb = models.ForeignKey(SomethingB, ...)
> date = models.DateField()
>
> class Meta:
> unique_together = ('fkb', 'date')
> }}}
>
> This can result in an automatically created migration (using `manage.py
> migrate`) that looks like this:
>
> {{{
> operations = [
> migrations.AddField(
> model_name='mymodel',
> name='fkb',
> field=models.ForeignKey(... to='myapp.somethingb'),
> ),
> migrations.RemoveField(
> model_name='mymodel',
> name='fka',
> ),
> migrations.AlterUniqueTogether(
> name='mymodel',
> unique_together={('fkb', 'date')},
> ),
> ]
> }}}
>
> This migration fails, because `AlterUniqueTogether` needs to come before
> `RemoveField`, as it references `fka`.
New description:
models.py before:
{{{
class MyModel(models.Model):
fka = models.ForeignKey(SomethingA, ...)
date = models.DateField()
class Meta:
unique_together = ('fka', 'date')
}}}
models.py after:
{{{
class MyModel(models.Model):
fkb = models.ForeignKey(SomethingB, ...)
date = models.DateField()
class Meta:
unique_together = ('fkb', 'date')
}}}
This can result in an automatically created migration (using `manage.py
makemigrations`) that looks like this:
{{{
operations = [
migrations.AddField(
model_name='mymodel',
name='fkb',
field=models.ForeignKey(... to='myapp.somethingb'),
),
migrations.RemoveField(
model_name='mymodel',
name='fka',
),
migrations.AlterUniqueTogether(
name='mymodel',
unique_together={('fkb', 'date')},
),
]
}}}
This migration fails, because `AlterUniqueTogether` needs to come before
`RemoveField`, as it references `fka`. This is hard to debug, and can only
be fixed by manually reordering the migration operations.
--
--
Ticket URL: <https://code.djangoproject.com/ticket/28916#comment:2>
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