Migration from ForeignKey to FileField fails: AttributeError: 'NoneType' object has no attribute 'to'

[Daniel Hahler]

The following migration fails to change the ForeignKey field into a FileField:

        migrations.AlterField(
            model_name='mainfile',
            name='file',
            field=models.FileField(upload_to='...'),
        ),

  Applying app.0017_auto_20140326_1849...Traceback (most recent call last):
  File "…/manage.py", line 62, in <module>
    execute_from_command_line(sys.argv)
  File "…/django-master/django/core/management/__init__.py", line 427, in execute_from_command_line
    utility.execute()
  File "…/django-master/django/core/management/__init__.py", line 419, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "…/django-master/django/core/management/base.py", line 288, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "…/django-master/django/core/management/base.py", line 337, in execute
    output = self.handle(*args, **options)
  File "…/django-master/django/core/management/commands/migrate.py", line 145, in handle
    executor.migrate(targets, plan, fake=options.get("fake", False))
  File "…/django-master/django/db/migrations/executor.py", line 60, in migrate
    self.apply_migration(migration, fake=fake)
  File "…/django-master/django/db/migrations/executor.py", line 94, in apply_migration
    migration.apply(project_state, schema_editor)
  File "…/django-master/django/db/migrations/migration.py", line 97, in apply
    operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
  File "…/django-master/django/db/migrations/operations/fields.py", line 127, in database_forwards
    from_field.rel.to = to_field.rel.to
AttributeError: 'NoneType' object has no attribute 'to'

ipdb> from_model, from_field, from_field.rel, to_field, to_field.rel

<class '__fake__.MainFile'>,
<django.db.models.fields.related.ForeignKey: file>
<django.db.models.fields.related.ManyToOneRel object at 0x4385410>
<django.db.models.fields.files.FileField: file>
None)

[Stephen Burrows]

I just ran into this with altering an M2M field to a text field. Workaround: Remove first, then re-add as text field.

[wlan]

I just had the same problem but with altering an M2M field into a booleanfield, the workaround posted by melinath worked for me as well.

[Andrew Godwin]

Can no longer reproduce, so marking as fixed.