refactor(user_solo): made field more generic

I realized that this could apply to more use cases if it just offered a
custom field.

user_solo/README.md

@@ -1,22 +1,17 @@
 # django-user-solo
 
-Proof of concept `UserSingletonModel` that creates an singleton instance for each user.
+Proof of concept `AutoOneToOneField` that creates an singleton instance for each user.
 
 Inspired by [django-solo](https://github.com/lazybird/django-solo) ❤️
 
 ```python
-from user_solo.models import UserSingletonModel
+from user_solo.models import AutoOneToOneField
 
-class Preference(UserSingletonModel):
+class Preference(models.Model):
+    user = AutoOneToOneField(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
     flag = models.BooleanField(default=True)
 
 # All users will have .preference
 user = User.objects.get(...)
 user.preference # get_or_create
 ```
-
-### TODO
-
-- Settings
-- Caching
-- Signals (create when user created)

user_solo/models.py

@@ -1,21 +1,13 @@
-from django.conf import settings
 from django.core.exceptions import ObjectDoesNotExist
-from django.db import models
 from django.db.models.fields.related_descriptors import ReverseOneToOneDescriptor
 from django.db.models.fields.related import OneToOneField
 
-class UserSingletonDescriptor(ReverseOneToOneDescriptor):
+class AutoReverseOneToOneDescriptor(ReverseOneToOneDescriptor):
     def __get__(self, user, cls=None):
         try:
             return super().__get__(user, cls)
         except ObjectDoesNotExist:
             return self.related.related_model.objects.create(user=user)
 
-class UserSingletonField(OneToOneField):
-    related_accessor_class = UserSingletonDescriptor
-
-class UserSingletonModel(models.Model):
-    user = UserSingletonField(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
-
-    class Meta:
-        abstract = True
+class AutoOneToOneField(OneToOneField):
+    related_accessor_class = AutoReverseOneToOneDescriptor