Django import error when trying to import a model from a different app

Question

I've gone through just about every Python/Django import StackOverflow question and I still can't fix this issue. In Django I am trying to create a new model that has a foreign key of a model in a different app. I don't appear to be able to import this.

I am running Python 3.8 on Windows 10, running within a clean virtual environment

Steps:

> pip install django
> django-admin startproject django1
> cd django1
> python manage.py startapp app1
> python manage.py startapp app2

Add both apps to the INSTALLED_APPS in django1/settings.py:

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'app1',
    'app2'
]

Create a model in app1/models.py:

from django.db import models


class App1Model1(models.Model):
    val1 = models.BooleanField()
    val2 = models.BooleanField()

Create a model in app2/models.py:

from django.db import models
from ..app1.models import App1Model1


class App2Model1(models.Model):
    ref1 = models.ForeignKey(App1Model1, on_delete=model.CASCASE)

Pycharm is fine with the relative import, but as soon as I run manage.py I get:

django1>python manage.py runserver
...
File "C:\DEV\sherpytest\django1\app2\models.py", line 2, in <module>
from ..app1.models import App1Model1
ValueError: attempted relative import beyond top-level package

If I change the import in app2\models.py to this:

from django.db import models
from django1.app1.models import App1Model1


class App2Model1(models.Model):
    ref1 = models.ForeignKey(App1Model1, on_delete=model.CASCASE)

I get:

django1>python manage.py runserver
...
File "C:\DEV\sherpytest\django1\app2\models.py", line 2, in <module>
from django1.app1.models import App1Model1
ModuleNotFoundError: No module named 'django1.app1'

I have tried creating a setup.py in django1 and installing it to turn it into a package (even though no tutorial tells me to do that) and still having issue.

Any help is greatly appreciated:)

Answer 1

When the structure is

- project root
  - manage.py
  - django1 (project)
  - app1 (app)
  - app2 (app)

you always import things with app1.models , app2.models , django1.somethingsomething , never with a relative import that'd go up to the "root" level where manage.py tends to live. (Naturally, if you have packages within your apps, you're free to use relative imports within them, but not across apps.)

That is,

from django.db import models
from app1.models import App1Model1

class App2Model1(models.Model):
    ref1 = models.ForeignKey(App1Model1, on_delete=models.CASCADE)

You can also refer to other apps' models by strings, to avoid some circular import issues:

from django.db import models

class App2Model1(models.Model):
    ref1 = models.ForeignKey("app1.App1Model1", on_delete=models.CASCADE)