id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
25247	makemigrations unable to generate necessary migration for making a superclass abstract	David Sanders	nobody	"If a user has an existing model state that uses model inheritance and changes a superclass to become abstract then makemigrations is unable to produce a suitable migration.  In fact the resulting migration will actually raise an exception when run.

This is non-trivial as a generated migration may require some data migration operations.

This was reported by a user on #django and I was able to reproduce with a small test:

{{{#!python

# Initial model state:

class Foo(models.Model):
    name = models.CharField(max_length=255)


class Bar(Foo):
    pass


# Subsequent model state:

class Foo(models.Model):
    name = models.CharField(max_length=255)

    class Meta:
        abstract=True


class Bar(Foo):
    pass


# running makemigrations results in:

class Migration(migrations.Migration):

    dependencies = [
        ('foobar', '0001_initial'),
    ]

    operations = [
        migrations.RemoveField(
            model_name='bar',
            name='foo_ptr',
        ),
        migrations.AddField(
            model_name='bar',
            name='id',
            field=models.AutoField(auto_created=True, primary_key=True, default=1, serialize=False, verbose_name='ID'),
            preserve_default=False,
        ),
        migrations.AddField(
            model_name='bar',
            name='name',
            field=models.CharField(default='asdf', max_length=255),
            preserve_default=False,
        ),
        migrations.DeleteModel(
            name='Foo',
        ),
    ]


# which results in the following when attempting to run migrate:

(env)dsanders ~/test/abstract_update/test_abstract $ ./manage.py migrate
Operations to perform:
  Synchronize unmigrated apps: staticfiles, messages
  Apply all migrations: admin, foobar, contenttypes, auth, sessions
Synchronizing apps without migrations:
  Creating tables...
    Running deferred SQL...
  Installing custom SQL...
Running migrations:
  Rendering model states...Traceback (most recent call last):
  File ""./manage.py"", line 10, in <module>
    execute_from_command_line(sys.argv)
  File ""/Users/dsanders/test/abstract_update/env/lib/python2.7/site-packages/django/core/management/__init__.py"", line 338, in execute_from_command_line
    utility.execute()
  File ""/Users/dsanders/test/abstract_update/env/lib/python2.7/site-packages/django/core/management/__init__.py"", line 330, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File ""/Users/dsanders/test/abstract_update/env/lib/python2.7/site-packages/django/core/management/base.py"", line 393, in run_from_argv
    self.execute(*args, **cmd_options)
  File ""/Users/dsanders/test/abstract_update/env/lib/python2.7/site-packages/django/core/management/base.py"", line 444, in execute
    output = self.handle(*args, **options)
  File ""/Users/dsanders/test/abstract_update/env/lib/python2.7/site-packages/django/core/management/commands/migrate.py"", line 221, in handle
    executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
  File ""/Users/dsanders/test/abstract_update/env/lib/python2.7/site-packages/django/db/migrations/executor.py"", line 104, in migrate
    state = migration.mutate_state(state, preserve=do_run)
  File ""/Users/dsanders/test/abstract_update/env/lib/python2.7/site-packages/django/db/migrations/migration.py"", line 83, in mutate_state
    operation.state_forwards(self.app_label, new_state)
  File ""/Users/dsanders/test/abstract_update/env/lib/python2.7/site-packages/django/db/migrations/operations/fields.py"", line 51, in state_forwards
    state.reload_model(app_label, self.model_name_lower)
  File ""/Users/dsanders/test/abstract_update/env/lib/python2.7/site-packages/django/db/migrations/state.py"", line 152, in reload_model
    self.apps.render_multiple(states_to_be_rendered)
  File ""/Users/dsanders/test/abstract_update/env/lib/python2.7/site-packages/django/db/migrations/state.py"", line 262, in render_multiple
    model.render(self)
  File ""/Users/dsanders/test/abstract_update/env/lib/python2.7/site-packages/django/db/migrations/state.py"", line 546, in render
    body,
  File ""/Users/dsanders/test/abstract_update/env/lib/python2.7/site-packages/django/db/models/base.py"", line 254, in __new__
    'base class %r' % (field.name, name, base.__name__)
django.core.exceptions.FieldError: Local field u'id' in class 'Bar' clashes with field of similar name from base class 'Foo'

}}}"	Cleanup/optimization	new	Migrations	1.8	Normal		abstract makemigrations		Accepted	0	0	0	0	0	0