AlterModelManagers migration is generated for all Models with custom Managers, which is not compatible with Django 1.8

[Michał Bońkowski]

We have a Model and a default_manager with a custom name:

class MyModel(models.Model):
    my_objects = models.Manager()

This creates a migration with a default manager though no manager is marked with use_in_migrations = True.

class Migration(migrations.Migration):

    operations = [
        migrations.CreateModel(
            name='MyModel',
            fields=[
                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
            ],
            options={
                'default_manager_name': 'my_objects',
            },
            managers=[
                ('my_objects', django.db.models.manager.Manager()),
            ],
        ),
    ]

According to https://code.djangoproject.com/ticket/26643#comment:5, we should not get this manager added to the state.

After some investigation, we can see that manager with any other name than objects will be added to the migration: ​https://github.com/django/django/blob/1.11.8/django/db/migrations/state.py#L537.

Edit:
Under Django 1.8 makemigrations does not create a migration, while in Django 1.11 it creates one.

[Michał Bońkowski]

In our case we resolved it by adding the following condition in migration files:

if VERSION >= (1, 10)
    operations = [
    ...
    ]
else:
    operations = []

[Tim Graham]

The behavior changed in c0cf73a57d7f77af348aeb854e7b4f670dc3cee7 which suggests the new behavior is desired.

To keep your migrations compatible with older versions of Django, you must ​generate them with the oldest version of Django that you wish to support, so I see no problem there.