Django migrations fail if AutoSlugField has manager set

[ggbaker]

I just updated from 1.7.2 to 1.8.0 and some models where I have specified a 'manager' argument on the AutoSlugField now break Django migrations. The situation is:

class SomeModel(models.Model):
    objects = SomeCustomManager()
    all_objects = models.Manager()
    slug = AutoSlugField(populate_from=_autoslug_function, manager=all_objects)

Then when I try to do a makemigrations:

$ python manage.py makemigrations polls
Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/tmp/foo/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 338, in execute_from_command_line
    utility.execute()
  File "/tmp/foo/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 330, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/tmp/foo/local/lib/python2.7/site-packages/django/core/management/base.py", line 390, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/tmp/foo/local/lib/python2.7/site-packages/django/core/management/base.py", line 441, in execute
    output = self.handle(*args, **options)
  File "/tmp/foo/local/lib/python2.7/site-packages/django/core/management/commands/makemigrations.py", line 125, in handle
    migration_name=self.migration_name,
  File "/tmp/foo/local/lib/python2.7/site-packages/django/db/migrations/autodetector.py", line 43, in changes
    changes = self._detect_changes(convert_apps, graph)
  File "/tmp/foo/local/lib/python2.7/site-packages/django/db/migrations/autodetector.py", line 142, in _detect_changes
    self.generate_renamed_models()
  File "/tmp/foo/local/lib/python2.7/site-packages/django/db/migrations/autodetector.py", line 417, in generate_renamed_models
    model_fields_def = self.only_relation_agnostic_fields(model_state.fields)
  File "/tmp/foo/local/lib/python2.7/site-packages/django/db/migrations/autodetector.py", line 80, in only_relation_agnostic_fields
    deconstruction = self.deep_deconstruct(field)
  File "/tmp/foo/local/lib/python2.7/site-packages/django/db/migrations/autodetector.py", line 67, in deep_deconstruct
    for key, value in kwargs.items()
  File "/tmp/foo/local/lib/python2.7/site-packages/django/db/migrations/autodetector.py", line 67, in <dictcomp>
    for key, value in kwargs.items()
  File "/tmp/foo/local/lib/python2.7/site-packages/django/db/migrations/autodetector.py", line 61, in deep_deconstruct
    path, args, kwargs = deconstructed
ValueError: too many values to unpack

The problem seems to be: AutoSlugField.deconstruct includes the 'manager' argument in the kwargs it returns; that is recursively passed into django.db.migrations.autodetector.MigrationAutodetector.deep_deconstruct. Since Mangers have a .deconstruct() method, it is called and returns the wrong kind of result.

The most obvious solution I see is to not include 'manager' in AutoSlugField.deconstruct. I don't see why the details of the manager would be important to the migration, but I might be missing a use-case.

[ggbaker]

Exact models.py used to trigger the traceback in the issue report

[Jaap Roes]

Workaround for now:

from autoslug import AutoSlugField as RealAutoSlugField

class AutoSlugField(RealAutoSlugField):
    # XXX: Work around https://bitbucket.org/neithere/django-autoslug/issues/34/django-migrations-fail-if-autoslugfield
    def deconstruct(self):
        name, path, args, kwargs = super(AutoSlugField, self).deconstruct()
        if 'manager' in kwargs:
            del kwargs['manager']
        return name, path, args, kwargs

[Phil B]

Any idea if this will get fixed in the main branch? We're using our own fork for now.

[Phil B]

This should be fixed once this pull request gets merged:

https://github.com/neithere/django-autoslug/pull/9

[Andy]

Thanks for the pull request, merged into master.