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/apps/config.py

@@ -5,6 +5,7 @@
 
 from django.core.exceptions import ImproperlyConfigured
 from django.utils.deprecation import RemovedInDjango41Warning
+from django.utils.functional import cached_property
 from django.utils.module_loading import import_string, module_has_submodule
 
 APPS_MODULE_NAME = 'apps'
@@ -55,6 +56,15 @@ def __init__(self, app_name, app_module):
     def __repr__(self):
         return '<%s: %s>' % (self.__class__.__name__, self.label)
 
+    @cached_property
+    def default_auto_field(self):
+        from django.conf import settings
+        return settings.DEFAULT_AUTO_FIELD
+
+    @property
+    def _is_default_auto_field_overridden(self):
+        return self.__class__.default_auto_field is not AppConfig.default_auto_field
+
     def _path_from_module(self, module):
         """Attempt to determine app's filesystem path from its module."""
         # See #21874 for extended discussion of the behavior of this method in

django/conf/app_template/apps.py-tpl

@@ -2,4 +2,5 @@ from django.apps import AppConfig
 
 
 class {{ camel_case_app_name }}Config(AppConfig):
+    default_auto_field = 'django.db.models.BigAutoField'
     name = '{{ app_name }}'

django/conf/global_settings.py

@@ -414,6 +414,9 @@ def gettext_noop(s):
 DEFAULT_TABLESPACE = ''
 DEFAULT_INDEX_TABLESPACE = ''
 
+# Default primary key field type.
+DEFAULT_AUTO_FIELD = 'django.db.models.AutoField'
+
 # Default X-Frame-Options header value
 X_FRAME_OPTIONS = 'DENY'
 

django/conf/project_template/project_name/settings.py-tpl

@@ -118,3 +118,8 @@ USE_TZ = True
 # https://docs.djangoproject.com/en/{{ docs_version }}/howto/static-files/
 
 STATIC_URL = '/static/'
+
+# Default primary key field type
+# https://docs.djangoproject.com/en/{{ docs_version }}/ref/settings/#default-auto-field
+
+DEFAULT_AUTO_FIELD = 'django.db.models.BigAutoField'

django/contrib/admin/apps.py

@@ -7,6 +7,7 @@
 class SimpleAdminConfig(AppConfig):
     """Simple AppConfig which does not do automatic discovery."""
 
+    default_auto_field = 'django.db.models.AutoField'
     default_site = 'django.contrib.admin.sites.AdminSite'
     name = 'django.contrib.admin'
     verbose_name = _("Administration")

django/contrib/auth/apps.py

@@ -11,6 +11,7 @@
 
 
 class AuthConfig(AppConfig):
+    default_auto_field = 'django.db.models.AutoField'
     name = 'django.contrib.auth'
     verbose_name = _("Authentication and Authorization")
 

django/contrib/contenttypes/apps.py

@@ -12,6 +12,7 @@
 
 
 class ContentTypesConfig(AppConfig):
+    default_auto_field = 'django.db.models.AutoField'
     name = 'django.contrib.contenttypes'
     verbose_name = _("Content Types")
 

django/contrib/flatpages/apps.py

@@ -3,5 +3,6 @@
 
 
 class FlatPagesConfig(AppConfig):
+    default_auto_field = 'django.db.models.AutoField'
     name = 'django.contrib.flatpages'
     verbose_name = _("Flat Pages")

django/contrib/gis/apps.py

@@ -4,6 +4,7 @@
 
 
 class GISConfig(AppConfig):
+    default_auto_field = 'django.db.models.AutoField'
     name = 'django.contrib.gis'
     verbose_name = _("GIS")
 

django/contrib/redirects/apps.py

@@ -3,5 +3,6 @@
 
 
 class RedirectsConfig(AppConfig):
+    default_auto_field = 'django.db.models.AutoField'
     name = 'django.contrib.redirects'
     verbose_name = _("Redirects")

django/contrib/sitemaps/apps.py

@@ -3,5 +3,6 @@
 
 
 class SiteMapsConfig(AppConfig):
+    default_auto_field = 'django.db.models.AutoField'
     name = 'django.contrib.sitemaps'
     verbose_name = _("Site Maps")

django/contrib/sites/apps.py

@@ -8,6 +8,7 @@
 
 
 class SitesConfig(AppConfig):
+    default_auto_field = 'django.db.models.AutoField'
     name = 'django.contrib.sites'
     verbose_name = _("Sites")
 

django/db/models/base.py

@@ -1290,10 +1290,35 @@ def check(cls, **kwargs):
                 *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."""

django/db/models/options.py

@@ -5,12 +5,13 @@
 
 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 @@ def _format_names_with_class(self, cls, objs):
             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 @@ def _prepare(self, model):
                 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):

docs/ref/applications.txt

@@ -90,6 +90,7 @@ would provide a proper name for the admin::
     from django.apps import AppConfig
 
     class RockNRollConfig(AppConfig):
+        default_auto_field = 'django.db.models.BigAutoField'
         name = 'rock_n_roll'
         verbose_name = "Rock ’n’ roll"
 
@@ -219,6 +220,16 @@ Configurable attributes
 
     By default, this attribute isn't set.
 
+.. attribute:: AppConfig.default_auto_field
+
+    .. versionadded:: 3.2
+
+    The implicit primary key type to add to models within this app. You can
+    use this to keep :class:`~django.db.models.AutoField` as the primary key
+    type for third party applications.
+
+    By default, this is the value of :setting:`DEFAULT_AUTO_FIELD`.
+
 Read-only attributes
 --------------------
 

docs/ref/checks.txt

@@ -378,6 +378,8 @@ Models
 * **models.W040**: ``<database>`` does not support indexes with non-key
   columns.
 * **models.E041**: ``constraints`` refers to the joined field ``<field name>``.
+* **models.W042**: Auto-created primary key used when not defining a primary
+  key type, by default ``django.db.models.AutoField``.
 
 Security
 --------

docs/ref/models/fields.txt

@@ -415,9 +415,12 @@ cross-site scripting attack.
 If ``True``, this field is the primary key for the model.
 
 If you don't specify ``primary_key=True`` for any field in your model, Django
-will automatically add an :class:`AutoField` to hold the primary key, so you
-don't need to set ``primary_key=True`` on any of your fields unless you want to
-override the default primary-key behavior. For more, see
+will automatically add a field to hold the primary key, so you don't need to
+set ``primary_key=True`` on any of your fields unless you want to override the
+default primary-key behavior. The type of auto-created primary key fields can
+be specified per app in :attr:`AppConfig.default_auto_field
+<django.apps.AppConfig.default_auto_field>` or globally in the
+:setting:`DEFAULT_AUTO_FIELD` setting. For more, see
 :ref:`automatic-primary-key-fields`.
 
 ``primary_key=True`` implies :attr:`null=False <Field.null>` and
@@ -428,6 +431,11 @@ The primary key field is read-only. If you change the value of the primary
 key on an existing object and then save it, a new object will be created
 alongside the old one.
 
+.. versionchanged:: 3.2
+
+    In older versions, auto-created primary key fields were always
+    :class:`AutoField`\s.
+
 ``unique``
 ----------
 

docs/ref/settings.txt

@@ -1245,6 +1245,17 @@ format has higher precedence and will be applied instead.
 See also :setting:`NUMBER_GROUPING`, :setting:`THOUSAND_SEPARATOR` and
 :setting:`USE_THOUSAND_SEPARATOR`.
 
+.. setting:: DEFAULT_AUTO_FIELD
+
+``DEFAULT_AUTO_FIELD``
+----------------------
+
+.. versionadded:: 3.2
+
+Default: ``'``:class:`django.db.models.AutoField`\ ``'``
+
+Default primary key field type to use for models that don't have a field with
+:attr:`primary_key=True <django.db.models.Field.primary_key>`.
 
 .. setting:: DEFAULT_CHARSET
 

docs/releases/3.2.txt

@@ -53,6 +53,48 @@ needed. As a consequence, it's deprecated.
 
 See :ref:`configuring-applications-ref` for full details.
 
+Customizing type of auto-created primary keys
+---------------------------------------------
+
+When defining a model, if no field in a model is defined with
+:attr:`primary_key=True <django.db.models.Field.primary_key>` an implicit
+primary key is added. The type of this implicit primary key can now be
+controlled via the :setting:`DEFAULT_AUTO_FIELD` setting and
+:attr:`AppConfig.default_auto_field <django.apps.AppConfig.default_auto_field>`
+attribute. No more needing to override primary keys in all models.
+
+Maintaining the historical behavior, the default value for
+:setting:`DEFAULT_AUTO_FIELD` is :class:`~django.db.models.AutoField`. Starting
+with 3.2 new projects are generated with :setting:`DEFAULT_AUTO_FIELD` set to
+:class:`~django.db.models.BigAutoField`. Also, new apps are generated with
+:attr:`AppConfig.default_auto_field <django.apps.AppConfig.default_auto_field>`
+set to :class:`~django.db.models.BigAutoField`. In a future Django release the
+default value of :setting:`DEFAULT_AUTO_FIELD` will be changed to
+:class:`~django.db.models.BigAutoField`.
+
+To avoid unwanted migrations in the future, either explicitly set
+:setting:`DEFAULT_AUTO_FIELD` to :class:`~django.db.models.AutoField`::
+
+    DEFAULT_AUTO_FIELD = 'django.db.models.AutoField'
+
+or configure it on a per-app basis::
+
+    from django.apps import AppConfig
+
+    class MyAppConfig(AppConfig):
+        default_auto_field = 'django.db.models.AutoField'
+        name = 'my_app'
+
+or on a per-model basis::
+
+    from django.db import models
+
+    class MyModel(models.Model):
+        id = models.AutoField(primary_key=True)
+
+In anticipation of the changing default, a system check will provide a warning
+if you do not have an explicit setting for :setting:`DEFAULT_AUTO_FIELD`.
+
 ``pymemcache`` support
 ----------------------
 

docs/topics/db/models.txt

@@ -259,11 +259,12 @@ details can be found in the :ref:`common model field option reference
 Automatic primary key fields
 ----------------------------
 
-By default, Django gives each model the following field::
+By default, Django gives each model an auto-incrementing primary key with the
+type specified per app in :attr:`AppConfig.default_auto_field
+<django.apps.AppConfig.default_auto_field>` or globally in the
+:setting:`DEFAULT_AUTO_FIELD` setting. For example::
 
-    id = models.AutoField(primary_key=True)
-
-This is an auto-incrementing primary key.
+    id = models.BigAutoField(primary_key=True)
 
 If you'd like to specify a custom primary key, specify
 :attr:`primary_key=True <Field.primary_key>` on one of your fields. If Django
@@ -273,6 +274,11 @@ sees you've explicitly set :attr:`Field.primary_key`, it won't add the automatic
 Each model requires exactly one field to have :attr:`primary_key=True
 <Field.primary_key>` (either explicitly declared or automatically added).
 
+.. versionchanged:: 3.2
+
+    In older versions, auto-created primary key fields were always
+    :class:`AutoField`\s.
+
 .. _verbose-field-names:
 
 Verbose field names

tests/admin_scripts/tests.py

@@ -61,6 +61,7 @@ def write_settings(self, filename, apps=None, is_dir=False, sdict=None, extra=No
                 settings_file.write("%s\n" % extra)
             exports = [
                 'DATABASES',
+                'DEFAULT_AUTO_FIELD',
                 'ROOT_URLCONF',
                 'SECRET_KEY',
             ]
@@ -2188,6 +2189,20 @@ def test_overlaying_app(self):
             "won't replace conflicting files."
         )
 
+    def test_template(self):
+        out, err = self.run_django_admin(['startapp', 'new_app'])
+        self.assertNoOutput(err)
+        app_path = os.path.join(self.test_dir, 'new_app')
+        self.assertIs(os.path.exists(app_path), True)
+        with open(os.path.join(app_path, 'apps.py')) as f:
+            content = f.read()
+            self.assertIn('class NewAppConfig(AppConfig)', content)
+            self.assertIn(
+                "default_auto_field = 'django.db.models.BigAutoField'",
+                content,
+            )
+            self.assertIn("name = 'new_app'", content)
+
 
 class DiffSettings(AdminScriptTestCase):
     """Tests for diffsettings management command."""