Django tests fails when using a specific model in a migration file

Question

I've manually created a data migration file for a specific Django 1.11 app:

from __future__ import unicode_literals
from django.db import migrations, models

def set_item_things(apps, schema_editor):
    MyModel = apps.get_model('my_app', 'MyModel')
    # NOTE: if I remove this line then the tests will work
    MyOtherModel = apps.get_model('my_other_app', 'MyOtherModel')

    for item in MyModel.objects.all():
        # NOTE: if I remove this line then the tests will work
        thingy = MyOtherModel.get(example_field=item.color) 
        item.other_thing = thingy
        item.save()

class Migration(migrations.Migration):
    dependencies = [
        ('contracts', '0014_my_previous_migration'),
    ]

    operations = [
        migrations.RunPython(set_item_things),
    ]

When I run python manage.py migrate everything works as expected.
But whenever I run my test using pytest I get this:

test setup failed
self = <django.db.migrations.state.StateApps object at 0x10714b2b0>
app_label = 'my_other_app'

    def get_app_config(self, app_label):
        """
            Imports applications and returns an app config for the given label.

            Raises LookupError if no application exists with this label.
            """
        self.check_apps_ready()
        try:
>           return self.app_configs[app_label]
E           KeyError: 'my_other_app'

So it looks like the app config is not properly configured, and that's already weird because the migrate command ran smoothly.

Anyway: this is the content of my_other_app/apps.py:

from django.apps import AppConfig

class MyOtherAppConfig(AppConfig):
    name = 'my_other_app'

And basically is very similar to all the others apps.py sitting in the other apps directories, except of course for the name.

So I think the configuration should be correct but for whatever reasons my tests won't run.

The only fix is to remove any reference to my_other_app from the migration file.

I've already tried to add this to the my_other_apps/__init__.py:

default_app_config = 'my_other_apps.apps.MyOtherAppConfig'

but nothing changes.

I've already tried to see if there are circular dependencies inside my_other_apps/models.py but it doesn't seems the case.

What am I missing here?

Answer 1

I've found the solution from a similar SO question: MyOtherModel comes from a different app so in my migration file I have to specify that app last migration as additional dependency, that is:

class Migration(migrations.Migration):
    dependencies = [
        ('contracts', '0014_my_previous_migration'),
        # THIS extra line solves the problem!
        ('my_other_app', '002_my_last_migration'),
    ]

    operations = [
        migrations.RunPython(set_item_things),
    ]