FieldDoesNotExist when running a migration that removes a deleted field from unique_together

[Bas ten Berge]

Hi,

I'm running into an issue when performing this change to this model:

class TopicOwnerThoughtStatus(models.Model):
    '''
    Registers topic owner stats

    '''
    thought = models.ForeignKey(Thought, help_text='Associates the state to a thought', db_index=True)
    user = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='topicownerstatus_set', help_text='Associates this state to an user')
    topic = models.ForeignKey(Topic, help_text='Associates this state to a thought and topic')
    notified_at = models.DateTimeField(null=True, blank=True, help_text='Contains the timestamp the topicowner was notified')
    shown_at = models.DateTimeField(null=True, blank=True, help_text='Contains the timestamp the topicowner viewed the thoughts')
    finished_at = models.DateTimeField(null=True, blank=True, help_text='Contains the timestamp the topicowner marked the topic closed')

    class Meta:
        unique_together = ('thought', 'user', 'topic', )
        ordering = ('thought', )
        verbose_name_plural = 'Topic owner status'

Changing this model to:

class TopicOwnerThoughtStatus(models.Model):
    '''
    Registers topic owner stats

    '''
    thought = models.ForeignKey(Thought, help_text='Associates the state to a thought', db_index=True)
    user = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='topicownerstatus_set', help_text='Associates this state to an user')
    topic_selector = models.CharField(max_length=36, null=True, blank=True, help_text='Contains the topic selector')
    notified_at = models.DateTimeField(null=True, blank=True, help_text='Contains the timestamp the topicowner was notified')
    shown_at = models.DateTimeField(null=True, blank=True, help_text='Contains the timestamp the topicowner viewed the thoughts')
    finished_at = models.DateTimeField(null=True, blank=True, help_text='Contains the timestamp the topicowner marked the topic closed')

    class Meta:
        unique_together = ('thought', 'user', 'topic_selector', )
        ordering = ('thought', )
        verbose_name_plural = 'Topic owner status'

will allow me to create a migration, but I'm not able to run that migration:

(env-brownpapersession)bastb@bastb-vps:/var/www/brownpapersession/dev/brownpapersession$ python manage.py migrate                                            Operations to perform:
  Apply all migrations: ..., topic
Running migrations:
  Applying topic.0014_auto_20170417_0941...Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/var/www/brownpapersession/dev/env-brownpapersession/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 363, in execute_from_command_line
    utility.execute()
  File "/var/www/brownpapersession/dev/env-brownpapersession/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 355, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/var/www/brownpapersession/dev/env-brownpapersession/local/lib/python2.7/site-packages/django/core/management/base.py", line 283, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/var/www/brownpapersession/dev/env-brownpapersession/local/lib/python2.7/site-packages/django/core/management/base.py", line 330, in execute
    output = self.handle(*args, **options)
  File "/var/www/brownpapersession/dev/env-brownpapersession/local/lib/python2.7/site-packages/django/core/management/commands/migrate.py", line 204, in handle
    fake_initial=fake_initial,
  File "/var/www/brownpapersession/dev/env-brownpapersession/local/lib/python2.7/site-packages/django/db/migrations/executor.py", line 115, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "/var/www/brownpapersession/dev/env-brownpapersession/local/lib/python2.7/site-packages/django/db/migrations/executor.py", line 145, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "/var/www/brownpapersession/dev/env-brownpapersession/local/lib/python2.7/site-packages/django/db/migrations/executor.py", line 244, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/var/www/brownpapersession/dev/env-brownpapersession/local/lib/python2.7/site-packages/django/db/migrations/migration.py", line 129, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "/var/www/brownpapersession/dev/env-brownpapersession/local/lib/python2.7/site-packages/django/db/migrations/operations/models.py", line 536, in database_forwards
    getattr(new_model._meta, self.option_name, set()),
  File "/var/www/brownpapersession/dev/env-brownpapersession/local/lib/python2.7/site-packages/django/db/backends/base/schema.py", line 348, in alter_unique_together
    self._delete_composed_index(model, fields, {'unique': True}, self.sql_delete_unique)
  File "/var/www/brownpapersession/dev/env-brownpapersession/local/lib/python2.7/site-packages/django/db/backends/base/schema.py", line 371, in _delete_composed_index
    columns = [model._meta.get_field(field).column for field in fields]
  File "/var/www/brownpapersession/dev/env-brownpapersession/local/lib/python2.7/site-packages/django/db/models/options.py", line 619, in get_field
    raise FieldDoesNotExist("%s has no field named '%s'" % (self.object_name, field_name))

I'm able to run this migration when following a two-step approach:

• add the topic_selector field
• change the unique_together to read ('thought', 'user', 'thought_selector', )
• create and run the migration
• remove the topic field
• create and run the migration

I'd expect to run this in one migration, though.

[Tim Graham]

Looks like a duplicate of #26180.