App without migrations depending on app with migrations fails on initial migrate call (postgres)

[Lucas Moeskops]

Simple test example:
In a new project add 'django.contrib.sites' and your main app to the INSTALLED APPS setting.
Use postgres as database.
Make a model in your main app that uses a relation to django.contrib.sites:

from django.contrib.sites.models import Site
class MyModel(models.Model):
  my_site = models.ForeignKey(Site)

Migrate the project:

python manage.py migrate

It will fail to migrate with the message: django.db.utils.ProgrammingError: relation "django_site" does not exist. This is because it tries to migrate the apps without migrations before the apps with migrations.

To solve the problem, the app should have at least one migration. But maybe this needs to be documented. I couldn't find it in the documentation.

[Simon Charette]

This is ​a documented limitation.

Be aware, however, that unmigrated apps cannot depend on migrated apps, by the very nature of not having migrations. This means that it is not generally possible to have an unmigrated app have a ForeignKey or ManyToManyField to a migrated app; some cases may work, but it will eventually fail.

[Lucas Moeskops]

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[Tim Graham]

I think improving the error message (about missing migrations) is tracked in #24484.