Migration to delete child model (multi-table inheritance) results in an error when using SQLite

[Alexandru Mărășteanu]

1. Create two models where one of them inherits the other:

   class Foo(models.Model):
       test = models.CharField(max_length=256)
   
   
   class Bar(Foo):
       pass
   

2. Generate and run migrations.

migrations/0001_initial.py is:

...
operations = [
    migrations.CreateModel(
        name='Foo',
        fields=[
            ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
            ('test', models.CharField(max_length=256)),
        ],
    ),
    migrations.CreateModel(
        name='Bar',
        fields=[
            ('foo_ptr', models.OneToOneField(auto_created=True, on_delete=django.db.models.deletion.CASCADE, parent_link=True, primary_key=True, serialize=False, to='foo.Foo')),
        ],
        bases=('foo.foo',),
    ),
]
...

3. Delete the child model (Bar)

4. Generate migrations

migrations/0002_auto_20170123_1212.py is:

...
operations = [
    migrations.RemoveField(
        model_name='bar',
        name='foo_ptr',
    ),
    migrations.DeleteModel(
        name='Bar',
    ),
]
...

5. Run migrations

   $ python manage.py migrate
   Operations to perform:
     Apply all migrations: admin, contenttypes, foo, auth, sessions
   Running migrations:
     Rendering model states... DONE
     Applying foo.0002_auto_20170123_1212...Traceback (most recent call last):
     File "manage.py", line 10, in <module>
       execute_from_command_line(sys.argv)
     File "/djbug/lib/python2.7/site-packages/django/core/management/__init__.py", line 353, in execute_from_command_line
       utility.execute()
     File "/djbug/lib/python2.7/site-packages/django/core/management/__init__.py", line 345, in execute
       self.fetch_command(subcommand).run_from_argv(self.argv)
     File "/djbug/lib/python2.7/site-packages/django/core/management/base.py", line 348, in run_from_argv
       self.execute(*args, **cmd_options)
     File "/djbug/lib/python2.7/site-packages/django/core/management/base.py", line 399, in execute
       output = self.handle(*args, **options)
     File "/djbug/lib/python2.7/site-packages/django/core/management/commands/migrate.py", line 200, in handle
       executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
     File "/djbug/lib/python2.7/site-packages/django/db/migrations/executor.py", line 92, in migrate
       self._migrate_all_forwards(plan, full_plan, fake=fake, fake_initial=fake_initial)
     File "/djbug/lib/python2.7/site-packages/django/db/migrations/executor.py", line 121, in _migrate_all_forwards
       state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
     File "/djbug/lib/python2.7/site-packages/django/db/migrations/executor.py", line 198, in apply_migration
       state = migration.apply(state, schema_editor)
     File "/djbug/lib/python2.7/site-packages/django/db/migrations/migration.py", line 123, in apply
       operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
     File "/djbug/lib/python2.7/site-packages/django/db/migrations/operations/fields.py", line 121, in database_forwards
       schema_editor.remove_field(from_model, from_model._meta.get_field(self.name))
     File "/djbug/lib/python2.7/site-packages/django/db/backends/sqlite3/schema.py", line 247, in remove_field
       self._remake_table(model, delete_fields=[field])
     File "/djbug/lib/python2.7/site-packages/django/db/backends/sqlite3/schema.py", line 197, in _remake_table
       self.quote_name(model._meta.db_table),
     File "/djbug/lib/python2.7/site-packages/django/db/backends/base/schema.py", line 110, in execute
       cursor.execute(sql, params)
     File "/djbug/lib/python2.7/site-packages/django/db/backends/utils.py", line 79, in execute
       return super(CursorDebugWrapper, self).execute(sql, params)
     File "/djbug/lib/python2.7/site-packages/django/db/backends/utils.py", line 64, in execute
       return self.cursor.execute(sql, params)
     File "/djbug/lib/python2.7/site-packages/django/db/utils.py", line 95, in __exit__
       six.reraise(dj_exc_type, dj_exc_value, traceback)
     File "/djbug/lib/python2.7/site-packages/django/db/backends/utils.py", line 64, in execute
       return self.cursor.execute(sql, params)
     File "/djbug/lib/python2.7/site-packages/django/db/backends/sqlite3/base.py", line 323, in execute
       return Database.Cursor.execute(self, query, params)
   django.db.utils.OperationalError: near ")": syntax error
   

Verified with Django (1.9.6 and 1.10.5) and SQLite 3 (sqlite3.version is 2.6.0) on macOS 10.12.2 with Python 2.7.12.