Django: AUTH_USER_MODEL vs get_user_model TLDR version

decisions..decisions..

i'll give Spartan-degree laconic reply and explain briefly

get_user_model good, AUTH_USER_MODEL safe

just know the limitations

get_user_model() returns the current active user model, even if it is a custom one. however, it runs (since it's a function call) when the app using it is first imported. if used (called) in an app higher in the INSTALLED_APPS hierachy than the referenced user model (if it's a custom one), it might break the import. you are referencing a non-existent user model aka it has not been imported. eg using it in a books app that refences a user in custom user model in a users app with INSTALLED_APPS in your settings.py looking as below;

you can see that at the time get_user_model() is called in the books app, it is referencing an app, users, that, in order of the hierarchy of imports in Django, has yet to be imported. this can break the import and the whole code.

AUTH_USER_MODEL will always delay the import of the user model specified untill all models (model classes) have been imported. the only catch here is if the custom user model define in the AUTH_USER_MODEL in the settings.py file is changed and the foreign key field references a field that does not exist in the defined model.

the two are imported as below;

get_user_model

class Book(models.Model):
    author = models.ForeignKey(User, on_delete=models.CASCADE)

AUTH_USER_MODEL

class Book(models.Model):
    author = models.ForeignKey(settings.AUTH_USER_MODEL,on_delete=models.CASCADE)