Viewing github.com/django/django-stable-4.1.x/docs/releases/3.1.txt

```
========================
```
```
Django 3.1 release notes
```
```
========================
```
```
*August 4, 2020*
```
```
Welcome to Django 3.1!
```

These release notes cover the :ref:`new features <whats-new-3.1>`, as well as

some :ref:`backwards incompatible changes <backwards-incompatible-3.1>` you'll

want to be aware of when upgrading from Django 3.0 or earlier. We've

:ref:`dropped some features<removed-features-3.1>` that have reached the end of

their deprecation cycle, and we've :ref:`begun the deprecation process for

some features <deprecated-features-3.1>`.

See the :doc:`/howto/upgrade-version` guide if you're updating an existing

```
project.
```
```
Python compatibility
```
```
====================
```

Django 3.1 supports Python 3.6, 3.7, 3.8, and 3.9 (as of 3.1.3). We **highly

recommend** and only officially support the latest release of each series.

```
.. _whats-new-3.1:
```
```
What's new in Django 3.1
```
```
========================
```

Asynchronous views and middleware support

-----------------------------------------

Django now supports a fully asynchronous request path, including:

* :ref:`Asynchronous views <async-views>`

* :ref:`Asynchronous middleware <async-middleware>`

* :ref:`Asynchronous tests and test client <async-tests>`

To get started with async views, you need to declare a view using

```
``async def``::
```
```
    async def my_view(request):
```
```
        await asyncio.sleep(0.5)
```

        return HttpResponse('Hello, async world!')

All asynchronous features are supported whether you are running under WSGI or

ASGI mode. However, there will be performance penalties using async code in

WSGI mode. You can read more about the specifics in :doc:`/topics/async`

```
documentation.
```

You are free to mix async and sync views, middleware, and tests as much as you

want. Django will ensure that you always end up with the right execution

context. We expect most projects will keep the majority of their views

synchronous, and only have a select few running in async mode - but it is

```
entirely your choice.
```

Django's ORM, cache layer, and other pieces of code that do long-running

network calls do not yet support async access. We expect to add support for

them in upcoming releases. Async views are ideal, however, if you are doing a

lot of API or HTTP calls inside your view, you can now natively do all those

HTTP calls in parallel to considerably speed up your view's execution.

Asynchronous support should be entirely backwards-compatible and we have tried

to ensure that it has no speed regressions for your existing, synchronous code.

It should have no noticeable effect on any existing Django projects.

JSONField for all supported database backends

---------------------------------------------

Django now includes :class:`.models.JSONField` and

:class:`forms.JSONField <django.forms.JSONField>` that can be used on all

supported database backends. Both fields support the use of custom JSON

encoders and decoders. The model field supports the introspection,

:ref:`lookups, and transforms <querying-jsonfield>` that were previously

```
PostgreSQL-only::
```
```
    from django.db import models
```
```
    class ContactInfo(models.Model):
```
```
        data = models.JSONField()
```
```
    ContactInfo.objects.create(data={
```
```
        'name': 'John',
```

        'cities': ['London', 'Cambridge'],

        'pets': {'dogs': ['Rufus', 'Meg']},

```
    })
```
```
    ContactInfo.objects.filter(
```
```
        data__name='John',
```
```
        data__pets__has_key='dogs',
```

        data__cities__contains='London',

```
    ).delete()
```

If your project uses ``django.contrib.postgres.fields.JSONField``, plus the

related form field and transforms, you should adjust to use the new fields,

and generate and apply a database migration. For now, the old fields and

transforms are left as a reference to the new ones and are :ref:`deprecated as

of this release <deprecated-jsonfield>`.

```
.. _default-hashing-algorithm-usage:
```
```
``DEFAULT_HASHING_ALGORITHM`` settings
```
```
--------------------------------------
```

The new ``DEFAULT_HASHING_ALGORITHM`` transitional setting allows specifying

the default hashing algorithm to use for encoding cookies, password reset

tokens in the admin site, user sessions, and signatures created by

:class:`django.core.signing.Signer` and :meth:`django.core.signing.dumps`.

Support for SHA-256 was added in Django 3.1. If you are upgrading multiple

instances of the same project to Django 3.1, you should set

``DEFAULT_HASHING_ALGORITHM`` to ``'sha1'`` during the transition, in order to

allow compatibility with the older versions of Django. Note that this requires

Django 3.1.1+. Once the transition to 3.1 is complete you can stop overriding

```
``DEFAULT_HASHING_ALGORITHM``.
```

This setting is deprecated as of this release, because support for tokens,

cookies, sessions, and signatures that use SHA-1 algorithm will be removed in

```
Django 4.0.
```
```
Minor features
```
```
--------------
```
```
:mod:`django.contrib.admin`
```
```
~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

* The new ``django.contrib.admin.EmptyFieldListFilter`` for

  :attr:`.ModelAdmin.list_filter` allows filtering on empty values (empty

  strings and nulls) in the admin changelist view.

* Filters in the right sidebar of the admin changelist view now contain a link

```
  to clear all filters.
```

* The admin now has a sidebar on larger screens for easier navigation. It is

  enabled by default but can be disabled by using a custom ``AdminSite`` and

  setting :attr:`.AdminSite.enable_nav_sidebar` to ``False``.

  Rendering the sidebar requires access to the current request in order to set

  CSS and ARIA role affordances. This requires using

  ``'django.template.context_processors.request'`` in the

  ``'context_processors'`` option of :setting:`OPTIONS <TEMPLATES-OPTIONS>`.

* Initially empty ``extra`` inlines can now be removed, in the same way as

```
  dynamically created ones.
```

* ``XRegExp`` is upgraded from version 2.0.0 to 3.2.0.

* jQuery is upgraded from version 3.4.1 to 3.5.1.

* Select2 library is upgraded from version 4.0.7 to 4.0.13.

```
:mod:`django.contrib.auth`
```
```
~~~~~~~~~~~~~~~~~~~~~~~~~~
```

* The default iteration count for the PBKDF2 password hasher is increased from

```
  180,000 to 216,000.
```

* The new :setting:`PASSWORD_RESET_TIMEOUT` setting allows defining the number

  of seconds a password reset link is valid for. This is encouraged instead of

  the deprecated ``PASSWORD_RESET_TIMEOUT_DAYS`` setting, which will be removed

```
  in Django 4.0.
```

* The password reset mechanism now uses the SHA-256 hashing algorithm. Support

  for tokens that use the old hashing algorithm remains until Django 4.0.

* :meth:`.AbstractBaseUser.get_session_auth_hash` now uses the SHA-256 hashing

  algorithm. Support for user sessions that use the old hashing algorithm

```
  remains until Django 4.0.
```
```
:mod:`django.contrib.contenttypes`
```
```
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

* The new :option:`remove_stale_contenttypes --include-stale-apps` option

  allows removing stale content types from previously installed apps that have

  been removed from :setting:`INSTALLED_APPS`.

```
:mod:`django.contrib.gis`
```
```
~~~~~~~~~~~~~~~~~~~~~~~~~
```

* :lookup:`relate` lookup is now supported on MariaDB.

* Added the :attr:`.LinearRing.is_counterclockwise` property.

* :class:`~django.contrib.gis.db.models.functions.AsGeoJSON` is now supported

```
  on Oracle.
```

* Added the :class:`~django.contrib.gis.db.models.functions.AsWKB` and

  :class:`~django.contrib.gis.db.models.functions.AsWKT` functions.

* Added support for PostGIS 3 and GDAL 3.

```
:mod:`django.contrib.humanize`
```
```
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

* :tfilter:`intword` template filter now supports negative integers.

```
:mod:`django.contrib.postgres`
```
```
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

* The new :class:`~django.contrib.postgres.indexes.BloomIndex` class allows

  creating ``bloom`` indexes in the database. The new

  :class:`~django.contrib.postgres.operations.BloomExtension` migration

  operation installs the ``bloom`` extension to add support for this index.

* :meth:`~django.db.models.Model.get_FOO_display` now supports

  :class:`~django.contrib.postgres.fields.ArrayField` and

  :class:`~django.contrib.postgres.fields.RangeField`.

* The new :lookup:`rangefield.lower_inc`, :lookup:`rangefield.lower_inf`,

  :lookup:`rangefield.upper_inc`, and :lookup:`rangefield.upper_inf` lookups

  allow querying :class:`~django.contrib.postgres.fields.RangeField` by a bound

```
  type.
```

* :lookup:`rangefield.contained_by` now supports

  :class:`~django.db.models.SmallAutoField`,

  :class:`~django.db.models.AutoField`,

  :class:`~django.db.models.BigAutoField`,

  :class:`~django.db.models.SmallIntegerField`, and

  :class:`~django.db.models.DecimalField`.

* :class:`~django.contrib.postgres.search.SearchQuery` now supports

  ``'websearch'`` search type on PostgreSQL 11+.

* :class:`SearchQuery.value <django.contrib.postgres.search.SearchQuery>` now

```
  supports query expressions.
```

* The new :class:`~django.contrib.postgres.search.SearchHeadline` class allows

```
  highlighting search results.
```

* :lookup:`search` lookup now supports query expressions.

* The new ``cover_density`` parameter of

  :class:`~django.contrib.postgres.search.SearchRank` allows ranking by cover

```
  density.
```

* The new ``normalization`` parameter of

  :class:`~django.contrib.postgres.search.SearchRank` allows rank

```
  normalization.
```

* The new :attr:`.ExclusionConstraint.deferrable` attribute allows creating

```
  deferrable exclusion constraints.
```
```
:mod:`django.contrib.sessions`
```
```
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

* The :setting:`SESSION_COOKIE_SAMESITE` setting now allows ``'None'`` (string)

  value to explicitly state that the cookie is sent with all same-site and

```
  cross-site requests.
```
```
:mod:`django.contrib.staticfiles`
```
```
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

* The :setting:`STATICFILES_DIRS` setting now supports :class:`pathlib.Path`.

```
Cache
```
```
~~~~~
```

* The :func:`~django.views.decorators.cache.cache_control` decorator and

  :func:`~django.utils.cache.patch_cache_control` method now support multiple

  field names in the ``no-cache`` directive for the ``Cache-Control`` header,

  according to :rfc:`7234#section-5.2.2.2`.

* :meth:`~django.core.caches.cache.delete` now returns ``True`` if the key was

  successfully deleted, ``False`` otherwise.

```
CSRF
```
```
~~~~
```

* The :setting:`CSRF_COOKIE_SAMESITE` setting now allows ``'None'`` (string)

  value to explicitly state that the cookie is sent with all same-site and

```
  cross-site requests.
```
```
Email
```
```
~~~~~
```

* The :setting:`EMAIL_FILE_PATH` setting, used by the :ref:`file email backend

  <topic-email-file-backend>`, now supports :class:`pathlib.Path`.

```
Error Reporting
```
```
~~~~~~~~~~~~~~~
```

* :class:`django.views.debug.SafeExceptionReporterFilter` now filters sensitive

  values from ``request.META`` in exception reports.

* The new :attr:`.SafeExceptionReporterFilter.cleansed_substitute` and

  :attr:`.SafeExceptionReporterFilter.hidden_settings` attributes allow

  customization of sensitive settings and ``request.META`` filtering in

```
  exception reports.
```

* The technical 404 debug view now respects

  :setting:`DEFAULT_EXCEPTION_REPORTER_FILTER` when applying settings

```
  filtering.
```

* The new :setting:`DEFAULT_EXCEPTION_REPORTER` allows providing a

  :class:`django.views.debug.ExceptionReporter` subclass to customize exception

  report generation. See :ref:`custom-error-reports` for details.

```
File Storage
```
```
~~~~~~~~~~~~
```

* ``FileSystemStorage.save()`` method now supports :class:`pathlib.Path`.

* :class:`~django.db.models.FileField` and

  :class:`~django.db.models.ImageField` now accept a callable for ``storage``.

  This allows you to modify the used storage at runtime, selecting different

  storages for different environments, for example.

```
Forms
```
```
~~~~~
```

* :class:`~django.forms.ModelChoiceIterator`, used by

  :class:`~django.forms.ModelChoiceField` and

  :class:`~django.forms.ModelMultipleChoiceField`, now uses

  :class:`~django.forms.ModelChoiceIteratorValue` that can be used by widgets

  to access model instances. See :ref:`iterating-relationship-choices` for

```
  details.
```

* :class:`django.forms.DateTimeField` now accepts dates in a subset of ISO 8601

  datetime formats, including optional timezone, e.g. ``2019-10-10T06:47``,

  ``2019-10-10T06:47:23+04:00``, or ``2019-10-10T06:47:23Z``. The timezone will

  always be retained if provided, with timezone-aware datetimes being returned

  even when :setting:`USE_TZ` is ``False``.

  Additionally, ``DateTimeField`` now uses ``DATE_INPUT_FORMATS`` in addition

  to ``DATETIME_INPUT_FORMATS`` when converting a field input to a ``datetime``

```
  value.
```

* :attr:`.MultiWidget.widgets` now accepts a dictionary which allows

  customizing subwidget ``name`` attributes.

* The new :attr:`.BoundField.widget_type` property can be used to dynamically

  adjust form rendering based upon the widget type.

```
Internationalization
```
```
~~~~~~~~~~~~~~~~~~~~
```

* The :setting:`LANGUAGE_COOKIE_SAMESITE` setting now allows ``'None'``

  (string) value to explicitly state that the cookie is sent with all same-site

```
  and cross-site requests.
```

* Added support and translations for the Algerian Arabic, Igbo, Kyrgyz, Tajik,

```
  and Turkmen languages.
```
```
Management Commands
```
```
~~~~~~~~~~~~~~~~~~~
```

* The new :option:`check --database` option allows specifying database aliases

  for running the ``database`` system checks. Previously these checks were

  enabled for all configured :setting:`DATABASES` by passing the ``database``

```
  tag to the command.
```

* The new :option:`migrate --check` option makes the command exit with a

  non-zero status when unapplied migrations are detected.

```
* The new ``returncode`` argument for
```

  :attr:`~django.core.management.CommandError` allows customizing the exit

```
  status for management commands.
```

* The new :option:`dbshell -- ARGUMENTS <dbshell -->` option allows passing

  extra arguments to the command-line client for the database.

* The :djadmin:`flush` and :djadmin:`sqlflush` commands now include SQL to

```
  reset sequences on SQLite.
```
```
Models
```
```
~~~~~~
```

* The new :class:`~django.db.models.functions.ExtractIsoWeekDay` function

  extracts ISO-8601 week days from :class:`~django.db.models.DateField` and

  :class:`~django.db.models.DateTimeField`, and the new :lookup:`iso_week_day`

  lookup allows querying by an ISO-8601 day of week.

* :meth:`.QuerySet.explain` now supports:

```
  * ``TREE`` format on MySQL 8.0.16+,
```

  * ``analyze`` option on MySQL 8.0.18+ and MariaDB.

* Added :class:`~django.db.models.PositiveBigIntegerField` which acts much like

  a :class:`~django.db.models.PositiveIntegerField` except that it only allows

  values under a certain (database-dependent) limit. Values from ``0`` to

  ``9223372036854775807`` are safe in all databases supported by Django.

* The new :class:`~django.db.models.RESTRICT` option for

  :attr:`~django.db.models.ForeignKey.on_delete` argument of ``ForeignKey`` and

  ``OneToOneField`` emulates the behavior of the SQL constraint ``ON DELETE

```
  RESTRICT``.
```

* :attr:`.CheckConstraint.check` now supports boolean expressions.

* The :meth:`.RelatedManager.add`, :meth:`~.RelatedManager.create`, and

  :meth:`~.RelatedManager.set` methods now accept callables as values in the

```
  ``through_defaults`` argument.
```

* The new ``is_dst``  parameter of the :meth:`.QuerySet.datetimes` determines

  the treatment of nonexistent and ambiguous datetimes.

* The new :class:`~django.db.models.F` expression ``bitxor()`` method allows

  :ref:`bitwise XOR operation <using-f-expressions-in-filters>`.

* :meth:`.QuerySet.bulk_create` now sets the primary key on objects when using

```
  MariaDB 10.5+.
```

* The ``DatabaseOperations.sql_flush()`` method now generates more efficient

  SQL on MySQL by using ``DELETE`` instead of ``TRUNCATE`` statements for

  tables which don't require resetting sequences.

* SQLite functions are now marked as :py:meth:`deterministic

  <sqlite3.Connection.create_function>` on Python 3.8+. This allows using them

  in check constraints and partial indexes.

* The new :attr:`.UniqueConstraint.deferrable` attribute allows creating

```
  deferrable unique constraints.
```
```
Pagination
```
```
~~~~~~~~~~
```

* :class:`~django.core.paginator.Paginator` can now be iterated over to yield

```
  its pages.
```
```
Requests and Responses
```
```
~~~~~~~~~~~~~~~~~~~~~~
```

* If :setting:`ALLOWED_HOSTS` is empty and ``DEBUG=True``, subdomains of

  localhost are now allowed in the ``Host`` header, e.g. ``static.localhost``.

* :meth:`.HttpResponse.set_cookie` and :meth:`.HttpResponse.set_signed_cookie`

  now allow using ``samesite='None'`` (string) to explicitly state that the

  cookie is sent with all same-site and cross-site requests.

* The new :meth:`.HttpRequest.accepts` method returns whether the request

  accepts the given MIME type according to the ``Accept`` HTTP header.

```
.. _whats-new-security-3.1:
```
```
Security
```
```
~~~~~~~~
```

* The :setting:`SECURE_REFERRER_POLICY` setting now defaults to

  ``'same-origin'``. With this configured,

  :class:`~django.middleware.security.SecurityMiddleware` sets the

  :ref:`referrer-policy` header to ``same-origin`` on all responses that do not

  already have it. This prevents the ``Referer`` header being sent to other

  origins. If you need the previous behavior, explicitly set

  :setting:`SECURE_REFERRER_POLICY` to ``None``.

* The default algorithm of :class:`django.core.signing.Signer`,

  :meth:`django.core.signing.loads`, and :meth:`django.core.signing.dumps` is

  changed to the SHA-256. Support for signatures made with the old SHA-1

```
  algorithm remains until Django 4.0.
```

  Also, the new ``algorithm`` parameter of the

  :class:`~django.core.signing.Signer` allows customizing the hashing

```
  algorithm.
```
```
Templates
```
```
~~~~~~~~~
```

* The renamed :ttag:`translate` and :ttag:`blocktranslate` template tags are

  introduced for internationalization in template code. The older :ttag:`trans`

  and :ttag:`blocktrans` template tags aliases continue to work, and will be

```
  retained for the foreseeable future.
```

* The :ttag:`include` template tag now accepts iterables of template names.

```
Tests
```
```
~~~~~
```

* :class:`~django.test.SimpleTestCase` now implements the ``debug()`` method to

  allow running a test without collecting the result and catching exceptions.

  This can be used to support running tests under a debugger.

* The new :setting:`MIGRATE <TEST_MIGRATE>` test database setting allows

  disabling of migrations during a test database creation.

* Django test runner now supports a :option:`test --buffer` option to discard

```
  output for passing tests.
```

* :class:`~django.test.runner.DiscoverRunner` now skips running the system

  checks on databases not :ref:`referenced by tests<testing-multi-db>`.

* :class:`~django.test.TransactionTestCase` teardown is now faster on MySQL

  due to :djadmin:`flush` command improvements. As a side effect the latter

  doesn't automatically reset sequences on teardown anymore. Enable

  :attr:`.TransactionTestCase.reset_sequences` if your tests require this

```
  feature.
```
```
URLs
```
```
~~~~
```

* :ref:`Path converters <registering-custom-path-converters>` can now raise

  ``ValueError`` in ``to_url()`` to indicate no match when reversing URLs.

```
Utilities
```
```
~~~~~~~~~
```

* :func:`~django.utils.encoding.filepath_to_uri` now supports

```
  :class:`pathlib.Path`.
```

* :func:`~django.utils.dateparse.parse_duration` now supports comma separators

  for decimal fractions in the ISO 8601 format.

* :func:`~django.utils.dateparse.parse_datetime`,

  :func:`~django.utils.dateparse.parse_duration`, and

  :func:`~django.utils.dateparse.parse_time` now support comma separators for

```
  milliseconds.
```
```
Miscellaneous
```
```
~~~~~~~~~~~~~
```

* The SQLite backend now supports :class:`pathlib.Path` for the ``NAME``

```
  setting.
```

* The ``settings.py`` generated by the :djadmin:`startproject` command now uses

  :class:`pathlib.Path` instead of :mod:`os.path` for building filesystem

```
  paths.
```

* The :setting:`TIME_ZONE <DATABASE-TIME_ZONE>` setting is now allowed on

```
  databases that support time zones.
```
```
.. _backwards-incompatible-3.1:
```
```
Backwards incompatible changes in 3.1
```
```
=====================================
```
```
Database backend API
```
```
--------------------
```

This section describes changes that may be needed in third-party database

```
backends.
```

* ``DatabaseOperations.fetch_returned_insert_columns()`` now requires an

  additional ``returning_params`` argument.

* ``connection.timezone`` property is now ``'UTC'`` by default, or the

  :setting:`TIME_ZONE <DATABASE-TIME_ZONE>` when :setting:`USE_TZ` is ``True``

  on databases that support time zones. Previously, it was ``None`` on

```
  databases that support time zones.
```

* ``connection._nodb_connection`` property is changed to the

  ``connection._nodb_cursor()`` method and now returns a context manager that

  yields a cursor and automatically closes the cursor and connection upon

```
  exiting the ``with`` statement.
```

* ``DatabaseClient.runshell()`` now requires an additional ``parameters``

  argument as a list of extra arguments to pass on to the command-line client.

* The ``sequences`` positional argument of ``DatabaseOperations.sql_flush()``

  is replaced by the boolean keyword-only argument ``reset_sequences``. If

  ``True``, the sequences of the truncated tables will be reset.

* The ``allow_cascade`` argument of ``DatabaseOperations.sql_flush()`` is now a

```
  keyword-only argument.
```
```
* The ``using`` positional argument of
```

  ``DatabaseOperations.execute_sql_flush()`` is removed. The method now uses

```
  the database of the called instance.
```

* Third-party database backends must implement support for ``JSONField`` or set

  ``DatabaseFeatures.supports_json_field`` to ``False``. If storing primitives

  is not supported, set ``DatabaseFeatures.supports_primitives_in_json_field``

  to ``False``. If there is a true datatype for JSON, set

  ``DatabaseFeatures.has_native_json_field`` to ``True``. If

  :lookup:`jsonfield.contains` and :lookup:`jsonfield.contained_by` are not

  supported, set ``DatabaseFeatures.supports_json_field_contains`` to

```
  ``False``.
```

* Third party database backends must implement introspection for ``JSONField``

  or set ``can_introspect_json_field`` to ``False``.

```
Dropped support for MariaDB 10.1
```
```
--------------------------------
```

Upstream support for MariaDB 10.1 ends in October 2020. Django 3.1 supports

```
MariaDB 10.2 and higher.
```
```
``contrib.admin`` browser support
```
```
---------------------------------
```

The admin no longer supports the legacy Internet Explorer browser. See

:ref:`the admin FAQ <admin-browser-support>` for details on supported browsers.

:attr:`AbstractUser.first_name <django.contrib.auth.models.User.first_name>` ``max_length`` increased to 150

------------------------------------------------------------------------------------------------------------

A migration for :attr:`django.contrib.auth.models.User.first_name` is included.

If you have a custom user model inheriting from ``AbstractUser``, you'll need

to generate and apply a database migration for your user model.

If you want to preserve the 30 character limit for first names, use a custom

```
form::
```
```
    from django import forms
```

    from django.contrib.auth.forms import UserChangeForm

    class MyUserChangeForm(UserChangeForm):

        first_name = forms.CharField(max_length=30, required=False)

If you wish to keep this restriction in the admin when editing users, set

```
``UserAdmin.form`` to use this form::
```

    from django.contrib.auth.admin import UserAdmin

    from django.contrib.auth.models import User

```
    class MyUserAdmin(UserAdmin):
```
```
        form = MyUserChangeForm
```
```
    admin.site.unregister(User)
```

    admin.site.register(User, MyUserAdmin)

```
Miscellaneous
```
```
-------------
```

* The cache keys used by :ttag:`cache` and generated by

  :func:`~django.core.cache.utils.make_template_fragment_key` are different

  from the keys generated by older versions of Django. After upgrading to

  Django 3.1, the first request to any previously cached template fragment will

```
  be a cache miss.
```

* The logic behind the decision to return a redirection fallback or a 204 HTTP

  response from the :func:`~django.views.i18n.set_language` view is now based

  on the ``Accept`` HTTP header instead of the ``X-Requested-With`` HTTP header

```
  presence.
```

* The compatibility imports of ``django.core.exceptions.EmptyResultSet`` in

  ``django.db.models.query``, ``django.db.models.sql``, and

  ``django.db.models.sql.datastructures`` are removed.

* The compatibility import of ``django.core.exceptions.FieldDoesNotExist`` in

  ``django.db.models.fields`` is removed.

* The compatibility imports of ``django.forms.utils.pretty_name()`` and

  ``django.forms.boundfield.BoundField`` in ``django.forms.forms`` are removed.

* The compatibility imports of ``Context``, ``ContextPopException``, and

  ``RequestContext`` in ``django.template.base`` are removed.

```
* The compatibility import of
```

  ``django.contrib.admin.helpers.ACTION_CHECKBOX_NAME`` in

```
  ``django.contrib.admin`` is removed.
```

* The :setting:`STATIC_URL` and :setting:`MEDIA_URL` settings set to relative

  paths are now prefixed by the server-provided value of ``SCRIPT_NAME`` (or

  ``/`` if not set). This change should not affect settings set to valid URLs

```
  or absolute paths.
```

* :class:`~django.middleware.http.ConditionalGetMiddleware` no longer adds the

  ``ETag`` header to responses with an empty

  :attr:`~django.http.HttpResponse.content`.

* ``django.utils.decorators.classproperty()`` decorator is made public and

  moved to :class:`django.utils.functional.classproperty()`.

* :tfilter:`floatformat` template filter now outputs (positive) ``0`` for

  negative numbers which round to zero.

* :attr:`Meta.ordering <django.db.models.Options.ordering>` and

  :attr:`Meta.unique_together <django.db.models.Options.unique_together>`

  options on models in ``django.contrib`` modules that were formerly tuples are

```
  now lists.
```

* The admin calendar widget now handles two-digit years according to the Open

  Group Specification, i.e. values between 69 and 99 are mapped to the previous

  century, and values between 0 and 68 are mapped to the current century.

* Date-only formats are removed from the default list for

```
  :setting:`DATETIME_INPUT_FORMATS`.
```

* The :class:`~django.forms.FileInput` widget no longer renders with the

  ``required`` HTML attribute when initial data exists.

* The undocumented ``django.views.debug.ExceptionReporterFilter`` class is

  removed. As per the :ref:`custom-error-reports` documentation, classes to be

  used with :setting:`DEFAULT_EXCEPTION_REPORTER_FILTER` need to inherit from

  :class:`django.views.debug.SafeExceptionReporterFilter`.

* The cache timeout set by :func:`~django.views.decorators.cache.cache_page`

  decorator now takes precedence over the ``max-age`` directive from the

```
  ``Cache-Control`` header.
```

* Providing a non-local remote field in the :attr:`.ForeignKey.to_field`

  argument now raises :class:`~django.core.exceptions.FieldError`.

* :setting:`SECURE_REFERRER_POLICY` now defaults to ``'same-origin'``. See the

  *What's New* :ref:`Security section <whats-new-security-3.1>` above for more

```
  details.
```

* :djadmin:`check` management command now runs the ``database`` system checks

  only for database aliases specified using :option:`check --database` option.

* :djadmin:`migrate` management command now runs the ``database`` system checks

```
  only for a database to migrate.
```

* The admin CSS classes ``row1`` and ``row2`` are removed in favor of

  ``:nth-child(odd)`` and ``:nth-child(even)`` pseudo-classes.

* The :func:`~django.contrib.auth.hashers.make_password` function now requires

  its argument to be a string or bytes. Other types should be explicitly cast

```
  to one of these.
```

* The undocumented ``version`` parameter to the

  :class:`~django.contrib.gis.db.models.functions.AsKML` function is removed.

* :ref:`JSON and YAML serializers <serialization-formats>`, used by

  :djadmin:`dumpdata`, now dump all data with Unicode by default. If you need

  the previous behavior, pass ``ensure_ascii=True`` to JSON serializer, or

  ``allow_unicode=False`` to YAML serializer.

* The auto-reloader no longer monitors changes in built-in Django translation

```
  files.
```

* The minimum supported version of ``mysqlclient`` is increased from 1.3.13 to

```
  1.4.0.
```

* The undocumented ``django.contrib.postgres.forms.InvalidJSONInput`` and

  ``django.contrib.postgres.forms.JSONString`` are moved to

```
  ``django.forms.fields``.
```

* The undocumented ``django.contrib.postgres.fields.jsonb.JsonAdapter`` class

```
  is removed.
```

* The :ttag:`{% localize off %} <localize>` tag and :tfilter:`unlocalize`

  filter no longer respect :setting:`DECIMAL_SEPARATOR` setting.

* The minimum supported version of ``asgiref`` is increased from 3.2 to

```
  3.2.10.
```

* The :doc:`Media </topics/forms/media>` class now renders ``<script>`` tags

  without the ``type`` attribute to follow `WHATWG recommendations

  <https://html.spec.whatwg.org/multipage/scripting.html#the-script-element>`_.

* :class:`~django.forms.ModelChoiceIterator`, used by

  :class:`~django.forms.ModelChoiceField` and

  :class:`~django.forms.ModelMultipleChoiceField`, now yields 2-tuple choices

  containing :class:`~django.forms.ModelChoiceIteratorValue` instances as the

  first ``value`` element in each choice. In most cases this proxies

  transparently, but if you need the ``field`` value itself, use the

  :attr:`.ModelChoiceIteratorValue.value` attribute instead.

```
.. _deprecated-features-3.1:
```
```
Features deprecated in 3.1
```
```
==========================
```
```
.. _deprecated-jsonfield:
```
```
PostgreSQL ``JSONField``
```
```
------------------------
```

``django.contrib.postgres.fields.JSONField`` and

``django.contrib.postgres.forms.JSONField`` are deprecated in favor of

```
:class:`.models.JSONField` and
```

:class:`forms.JSONField <django.forms.JSONField>`.

The undocumented ``django.contrib.postgres.fields.jsonb.KeyTransform`` and

``django.contrib.postgres.fields.jsonb.KeyTextTransform`` are also deprecated

in favor of the transforms in ``django.db.models.fields.json``.

The new ``JSONField``\s, ``KeyTransform``, and ``KeyTextTransform`` can be used

```
on all supported database backends.
```
```
Miscellaneous
```
```
-------------
```

* ``PASSWORD_RESET_TIMEOUT_DAYS`` setting is deprecated in favor of

```
  :setting:`PASSWORD_RESET_TIMEOUT`.
```

* The undocumented usage of the :lookup:`isnull` lookup with non-boolean values

  as the right-hand side is deprecated, use ``True`` or ``False`` instead.

* The barely documented ``django.db.models.query_utils.InvalidQuery`` exception

```
  class is deprecated in favor of
```

  :class:`~django.core.exceptions.FieldDoesNotExist` and

  :class:`~django.core.exceptions.FieldError`.

* The ``django-admin.py`` entry point is deprecated in favor of

```
  ``django-admin``.
```

* The ``HttpRequest.is_ajax()`` method is deprecated as it relied on a

  jQuery-specific way of signifying AJAX calls, while current usage tends to

```
  use the JavaScript `Fetch API
```

  <https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API>`_. Depending on

  your use case, you can either write your own AJAX detection method, or use

  the new :meth:`.HttpRequest.accepts` method if your code depends on the

```
  client ``Accept`` HTTP header.
```

  If you are writing your own AJAX detection method, ``request.is_ajax()`` can

```
  be reproduced exactly as
```

  ``request.headers.get('x-requested-with') == 'XMLHttpRequest'``.

* Passing ``None`` as the first argument to

  ``django.utils.deprecation.MiddlewareMixin.__init__()`` is deprecated.

* The encoding format of cookies values used by

  :class:`~django.contrib.messages.storage.cookie.CookieStorage` is different

  from the format generated by older versions of Django. Support for the old

```
  format remains until Django 4.0.
```

* The encoding format of sessions is different from the format generated by

  older versions of Django. Support for the old format remains until Django

```
  4.0.
```

* The purely documentational ``providing_args`` argument for

  :class:`~django.dispatch.Signal` is deprecated. If you rely on this

  argument as documentation, you can move the text to a code comment or

```
  docstring.
```

* Calling ``django.utils.crypto.get_random_string()`` without a ``length``

```
  argument is deprecated.
```

* The ``list`` message for :class:`~django.forms.ModelMultipleChoiceField` is

  deprecated in favor of ``invalid_list``.

* Passing raw column aliases to :meth:`.QuerySet.order_by` is deprecated. The

  same result can be achieved by passing aliases in a

  :class:`~django.db.models.expressions.RawSQL` instead beforehand.

* The ``NullBooleanField`` model field is deprecated in favor of

```
  ``BooleanField(null=True)``.
```

* ``django.conf.urls.url()`` alias of :func:`django.urls.re_path` is

```
  deprecated.
```

* The ``{% ifequal %}`` and ``{% ifnotequal %}`` template tags are deprecated

  in favor of :ttag:`{% if %}<if>`. ``{% if %}`` covers all use cases, but if

  you need to continue using these tags, they can be extracted from Django to a

  module and included as a built-in tag in the :class:`'builtins'

  <django.template.backends.django.DjangoTemplates>` option in

  :setting:`OPTIONS <TEMPLATES-OPTIONS>`.

* ``DEFAULT_HASHING_ALGORITHM`` transitional setting is deprecated.

```
.. _removed-features-3.1:
```
```
Features removed in 3.1
```
```
=======================
```

These features have reached the end of their deprecation cycle and are removed

```
in Django 3.1.
```

See :ref:`deprecated-features-2.2` for details on these changes, including how

```
to remove usage of these features.
```

* ``django.utils.timezone.FixedOffset`` is removed.

* ``django.core.paginator.QuerySetPaginator`` is removed.

* A model's ``Meta.ordering`` doesn't affect ``GROUP BY`` queries.

* ``django.contrib.postgres.fields.FloatRangeField`` and

  ``django.contrib.postgres.forms.FloatRangeField`` are removed.

* The ``FILE_CHARSET`` setting is removed.

* ``django.contrib.staticfiles.storage.CachedStaticFilesStorage`` is removed.

* The ``RemoteUserBackend.configure_user()`` method requires ``request`` as the

```
  first positional argument.
```

* Support for ``SimpleTestCase.allow_database_queries`` and

  ``TransactionTestCase.multi_db`` is removed.