From b5e12d490af3debca8c55ab3c1698189fdedbbdb Mon Sep 17 00:00:00 2001
From: Tom Forbes <tom@tomforb.es>
Date: Sun, 12 Jul 2020 13:59:57 +0100
Subject: Fixed #31007 -- Allowed specifying type of auto-created primary keys.

This also changes the default type of auto-created primary keys
for new apps and projects to BigAutoField.
---
 django/db/models/base.py    | 25 +++++++++++++++++++++++++
 django/db/models/options.py | 37 +++++++++++++++++++++++++++++++++++--
 2 files changed, 60 insertions(+), 2 deletions(-)

(limited to 'django/db/models')

diff --git a/django/db/models/base.py b/django/db/models/base.py
index de044886c3..822aad080d 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -1290,10 +1290,35 @@ class Model(metaclass=ModelBase):
                 *cls._check_indexes(databases),
                 *cls._check_ordering(),
                 *cls._check_constraints(databases),
+                *cls._check_default_pk(),
             ]
 
         return errors
 
+    @classmethod
+    def _check_default_pk(cls):
+        if (
+            cls._meta.pk.auto_created and
+            not settings.is_overridden('DEFAULT_AUTO_FIELD') and
+            not cls._meta.app_config._is_default_auto_field_overridden
+        ):
+            return [
+                checks.Warning(
+                    f"Auto-created primary key used when not defining a "
+                    f"primary key type, by default "
+                    f"'{settings.DEFAULT_AUTO_FIELD}'.",
+                    hint=(
+                        f"Configure the DEFAULT_AUTO_FIELD setting or the "
+                        f"{cls._meta.app_config.__class__.__qualname__}."
+                        f"default_auto_field attribute to point to a subclass "
+                        f"of AutoField, e.g. 'django.db.models.BigAutoField'."
+                    ),
+                    obj=cls,
+                    id='models.W042',
+                ),
+            ]
+        return []
+
     @classmethod
     def _check_swappable(cls):
         """Check if the swapped model exists."""
diff --git a/django/db/models/options.py b/django/db/models/options.py
index 0e28b6812a..4028e05b99 100644
--- a/django/db/models/options.py
+++ b/django/db/models/options.py
@@ -5,12 +5,13 @@ from collections import defaultdict
 
 from django.apps import apps
 from django.conf import settings
-from django.core.exceptions import FieldDoesNotExist
+from django.core.exceptions import FieldDoesNotExist, ImproperlyConfigured
 from django.db import connections
 from django.db.models import AutoField, Manager, OrderWrt, UniqueConstraint
 from django.db.models.query_utils import PathInfo
 from django.utils.datastructures import ImmutableList, OrderedSet
 from django.utils.functional import cached_property
+from django.utils.module_loading import import_string
 from django.utils.text import camel_case_to_spaces, format_lazy
 from django.utils.translation import override
 
@@ -217,6 +218,37 @@ class Options:
             new_objs.append(obj)
         return new_objs
 
+    def _get_default_pk_class(self):
+        pk_class_path = getattr(
+            self.app_config,
+            'default_auto_field',
+            settings.DEFAULT_AUTO_FIELD,
+        )
+        if self.app_config and self.app_config._is_default_auto_field_overridden:
+            app_config_class = type(self.app_config)
+            source = (
+                f'{app_config_class.__module__}.'
+                f'{app_config_class.__qualname__}.default_auto_field'
+            )
+        else:
+            source = 'DEFAULT_AUTO_FIELD'
+        if not pk_class_path:
+            raise ImproperlyConfigured(f'{source} must not be empty.')
+        try:
+            pk_class = import_string(pk_class_path)
+        except ImportError as e:
+            msg = (
+                f"{source} refers to the module '{pk_class_path}' that could "
+                f"not be imported."
+            )
+            raise ImproperlyConfigured(msg) from e
+        if not issubclass(pk_class, AutoField):
+            raise ValueError(
+                f"Primary key '{pk_class_path}' referred by {source} must "
+                f"subclass AutoField."
+            )
+        return pk_class
+
     def _prepare(self, model):
         if self.order_with_respect_to:
             # The app registry will not be ready at this point, so we cannot
@@ -250,7 +282,8 @@ class Options:
                 field.primary_key = True
                 self.setup_pk(field)
             else:
-                auto = AutoField(verbose_name='ID', primary_key=True, auto_created=True)
+                pk_class = self._get_default_pk_class()
+                auto = pk_class(verbose_name='ID', primary_key=True, auto_created=True)
                 model.add_to_class('id', auto)
 
     def add_manager(self, manager):
-- 
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