AttributeError during replaying/loading of migration: 'module' object has no attribute 'RemovedModel'

[Daniel Hahler]

I am getting a AttributeError when the existing migrations get loaded, but the model has been removed.

It looks like the migrations would have to refer to the to, through and possibly other arguments by string?!

The migration:

    operations = [
        migrations.AddField(
            model_name='model',
            name='country_of_origin',
            field=taggit.managers.TaggableManager(to=app.models.CountryOfOriginTag, through=app.models.TaggedCountryOfOrigin, blank=True, help_text=u'A comma-separated list of tags.', verbose_name=u'Country of origin'),
            preserve_default=True,
        ),
    ]

    Traceback (most recent call last):
      File "/home/user/.virtualenvs/project/bin/manage.py", line 62, in <module>
        execute_from_command_line(sys.argv)
      File "…/django/django/core/management/__init__.py", line 427, in execute_from_command_line
        utility.execute()
      File "…/django/django/core/management/__init__.py", line 419, in execute
        self.fetch_command(subcommand).run_from_argv(self.argv)
      File "…/django/django/core/management/base.py", line 288, in run_from_argv
        self.execute(*args, **options.__dict__)
      File "…/django/django/core/management/base.py", line 337, in execute
        output = self.handle(*args, **options)
      File "…/django/django/core/management/commands/makemigrations.py", line 56, in handle
        loader.build_graph(ignore_unmigrated=True)
      File "…/django/django/db/migrations/loader.py", line 145, in build_graph
        self.load_disk()
      File "…/django/django/db/migrations/loader.py", line 103, in load_disk
        migration_module = import_module("%s.%s" % (module_name, migration_name))
      File "/usr/lib/python2.7/importlib/__init__.py", line 37, in import_module
        __import__(name)
      File "…/project/app/migrations/0006_movie_country_of_origin.py", line 7, in <module>
        class Migration(migrations.Migration):
      File "…/project/app/migrations/0006_movie_country_of_origin.py", line 17, in Migration
        field=taggit.managers.TaggableManager(to=app.models.CountryOfOriginTag, through=app.models.TaggedCountryOfOrigin, blank=True, help_text=u'A comma-separated list of tags.', verbose_name=u'Country of origin'),
    AttributeError: 'module' object has no attribute 'CountryOfOriginTag'

[loic84]

Hi @blueyed, could you check if ​https://github.com/loic/django/compare/ticket22371 works?

I'm not convinced serializing models automatically is the best approach though, it probably doesn't work well with swappable models.

Maybe the right fix is to have taggit's deconstruct do a little more work.

[Daniel Hahler]

Thanks!

Unfortunately I've worked around this already, and have no time currently to get back to the old state.

[Tim Graham]

If we don't accept Loic's patch, then maybe some documentation about this situation would help?

[Tim Graham]

Loic, any thoughts on if we should do anything here?

[loic84]

I'm not completely convinced this is needed, TaggableManager could provide a deconstruct method and handle serializing Model objects. That said if models as arguments are common enough we could support them out of the box.

I don't think a documentation fix is warranted, we already document what types are supported by the serializer.

I'd let Andrew decide if we should go with the proposed fix or wontfix the ticket, it's just a matter of making a decision so bumping the ticket to Release Blocker.

[Andrew Godwin]

Yep, I'm WONTFIXing this. Taggable needs to return those as strings and do the lookups in the app registry itself (if it doesn't already); migrations won't freeze model references, down that path madness lies.

Note for taggable people: The apps registry you want to use is the one on the model, i.e. model._meta.apps - that way model versioning will work correctly.