Migration created on python2.7 fails to load on python 3 due to models.Manager

[Reto Aebersold]

If I create a migration on python 2.7 containing a model referencing a model.Manager with use_in_migrations = True the following line is added in the migration file:

managers=[
                (b'objects', accounts.models.UserManager()),
            ],

If I try to load this file under python 3.4 I get the error TypeError: attribute name must be string, not 'bytes from ​this line.

The problem is that the string 'objects' is prefixed with 'b' on ​this line.
I think this is maybe a bug as all other attribute names are just plain strings.

[Markus Holtermann]

Can you please post the entire traceback and the code you are using to define the model and manager.

[Reto Aebersold]

On python 2.7

models.py

from django.db import models


class MyManager(models.Manager):
    use_in_migrations = True

    def something(self):
        print('demo manager')


class MyModel(models.Model):
    demo = models.BooleanField(default=True)

    objects = MyManager()

0001_initial.py

# -*- coding: utf-8 -*-
from __future__ import unicode_literals

from django.db import models, migrations
import demo.models


class Migration(migrations.Migration):

    dependencies = [
    ]

    operations = [
        migrations.CreateModel(
            name='MyModel',
            fields=[
                ('id', models.AutoField(verbose_name='ID', serialize=False, auto_created=True, primary_key=True)),
                ('demo', models.BooleanField(default=True)),
            ],
            managers=[
                (b'objects', demo.models.MyManager()),
            ],
        ),
    ]

On python 3.4

$ ./manage.py migrate demo

Operations to perform:
  Apply all migrations: demo
Running migrations:
  Rendering model states...Traceback (most recent call last):
  File "./manage.py", line 35, in <module>
    execute_from_command_line(sys.argv)
  File "/home/aeby/code/myproject/venv/lib/python3.4/site-packages/django/core/management/__init__.py", line 338, in execute_from_command_line
    utility.execute()
  File "/home/aeby/code/myproject/venv/lib/python3.4/site-packages/django/core/management/__init__.py", line 330, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/aeby/code/myproject/venv/lib/python3.4/site-packages/django/core/management/base.py", line 390, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/home/aeby/code/myproject/venv/lib/python3.4/site-packages/django/core/management/base.py", line 441, in execute
    output = self.handle(*args, **options)
  File "/home/aeby/code/myproject/venv/lib/python3.4/site-packages/django/core/management/commands/migrate.py", line 221, in handle
    executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
  File "/home/aeby/code/myproject/venv/lib/python3.4/site-packages/django/db/migrations/executor.py", line 104, in migrate
    state = migration.mutate_state(state, preserve=do_run)
  File "/home/aeby/code/myproject/venv/lib/python3.4/site-packages/django/db/migrations/migration.py", line 83, in mutate_state
    operation.state_forwards(self.app_label, new_state)
  File "/home/aeby/code/myproject/venv/lib/python3.4/site-packages/django/db/migrations/operations/models.py", line 53, in state_forwards
    list(self.managers),
  File "/home/aeby/code/myproject/venv/lib/python3.4/site-packages/django/db/migrations/state.py", line 81, in add_model
    self.reload_model(app_label, model_name)
  File "/home/aeby/code/myproject/venv/lib/python3.4/site-packages/django/db/migrations/state.py", line 140, in reload_model
    self.apps.render_multiple(states_to_be_rendered)
  File "/home/aeby/code/myproject/venv/lib/python3.4/site-packages/django/db/migrations/state.py", line 250, in render_multiple
    model.render(self)
  File "/home/aeby/code/myproject/venv/lib/python3.4/site-packages/django/db/migrations/state.py", line 533, in render
    body,
  File "/home/aeby/code/myproject/venv/lib/python3.4/site-packages/django/db/models/base.py", line 189, in __new__
    new_class.add_to_class(obj_name, obj)
  File "/home/aeby/code/myproject/venv/lib/python3.4/site-packages/django/db/models/base.py", line 324, in add_to_class
    value.contribute_to_class(cls, name)
  File "/home/aeby/code/myproject/venv/lib/python3.4/site-packages/django/db/models/manager.py", line 169, in contribute_to_class
    setattr(model, name, ManagerDescriptor(self))
TypeError: attribute name must be string, not 'bytes'

[Simon Charette]

It looks like we'll need special casing of manager attribute name here ​just like we do with model fields.

[Markus Holtermann]

PR: ​https://github.com/django/django/pull/4558

[Markus Holtermann <info@…>]

In faad607:

Fixed #24701 -- Converted model manager names to unicode in migrations

Thanks to Reto Aebersold for reporting the issue and Tim Graham and
Claude Paroz for the review.

[Markus Holtermann <info@…>]

In 419f2962:

[1.8.x] Fixed #24701 -- Converted model manager names to unicode in migrations

Thanks to Reto Aebersold for reporting the issue and Tim Graham and
Claude Paroz for the review.

Backport of faad6070ee2eeea270c76381f9ca5999bf1ac15f from master

[Reto Aebersold]

Wow, you are fast. Thanks & respect!