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.

6 files changed, 87 insertions, 7 deletions

diff --git a/docs/ref/applications.txt b/docs/ref/applications.txt
index 765e9e8d3c..2cf175e9f0 100644
--- a/docs/ref/applications.txt
+++ b/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
 --------------------
 
diff --git a/docs/ref/checks.txt b/docs/ref/checks.txt
index 2ac5d4cb1d..a6e66d462f 100644
--- a/docs/ref/checks.txt
+++ b/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
 --------
diff --git a/docs/ref/models/fields.txt b/docs/ref/models/fields.txt
index 93c011fe2c..759e004fcf 100644
--- a/docs/ref/models/fields.txt
+++ b/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``
 ----------
 
diff --git a/docs/ref/settings.txt b/docs/ref/settings.txt
index bfa62f1508..8cb14e9768 100644
--- a/docs/ref/settings.txt
+++ b/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
 
diff --git a/docs/releases/3.2.txt b/docs/releases/3.2.txt
index 93b60690b3..5b1969698c 100644
--- a/docs/releases/3.2.txt
+++ b/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
 ----------------------
 
diff --git a/docs/topics/db/models.txt b/docs/topics/db/models.txt
index 81eb5b516b..26a6d7dc58 100644
--- a/docs/topics/db/models.txt
+++ b/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