Django - Circular model import issue

Question

Remove the import of Theme and use the model name as a string instead.

theme = models.ForeignKey('themes.Theme')

Upto Django 1.7:

Use get_model function from django.db.models which is designed for lazy model imports.:

from django.db.models import get_model
MyModel = get_model('app_name', 'ModelName')

In your case:

from django.db.models import get_model
Theme = get_model('themes', 'Theme')

Now you can use Theme

For Django 1.7+:

from django.apps import apps
apps.get_model('app_label.model_name')

Something I haven't seen mentioned anywhere in sufficient detail is how to properly formulate the string inside ForeignKey when referencing a model in a different app. This string needs to be app_label.model_name. And, very importantly, the app_label is not the entire line in INSTALLED_APPS, but only the last component of it. So if your INSTALLED_APPS looks like this:

INSTALLED_APPS = (
...
    'path.to.app1',
    'another.path.to.app2'
)

then to include a ForeignKey to a model in app2 in an app1 model, you must do:

app2_themodel = ForeignKey('app2.TheModel')

I spent quite a long time trying to solve a circular import issue (so I couldn't just from another.path.to.app2.models import TheModel) before I stumbled onto this, google/SO was no help (all the examples had single component app paths), so hopefully this will help other django newbies.

Since Django 1.7 correct way is to go like this:

from django.apps import apps

YourModel = apps.get_model('your_app_name', 'YourModel')

See: https://docs.djangoproject.com/ja/1.9/ref/applications/#django.apps.apps.get_model