Reading the Django Documentation:
get_user_model()
Instead of referring to User directly, you should reference the user model using django.contrib.auth.get_user_model(). This method will return the currently active User model – the custom User model if one is specified, or User otherwise.
When you define a foreign key or many-to-many relations to the User model, you should specify the custom model using the AUTH_USER_MODEL setting.
I'm confused with the above text. Should I be doing this:
author = models.ForeignKey(settings.AUTH_USER_MODEL)
or this...
author = models.ForeignKey(get_user_model())
Both seem to work.
Using settings.AUTH_USER_MODEL will delay the retrieval of the actual model class until all apps are loaded. get_user_model will attempt to retrieve the model class at the moment your app is imported the first time.
get_user_model cannot guarantee that the User model is already loaded into the app cache. It might work in your specific setup, but it is a hit-and-miss scenario. If you change some settings (e.g. the order of INSTALLED_APPS) it might very well break the import and you will have to spend additional time debugging.
settings.AUTH_USER_MODEL will pass a string as the foreign key model, and if the retrieval of the model class fails at the time this foreign key is imported, the retrieval will be delayed until all model classes are loaded into the cache.