<commit_before>============================================
Django 3.1 release notes - UNDER DEVELOPMENT
============================================

*Expected August 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, and 3.8. 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, lookups, and
transforms that were previously PostgreSQL-only.

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>`.

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>`.

* ``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, Kyrgyz, and Tajik
  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.

Migrations
~~~~~~~~~~

* Migrations are now loaded also from directories without ``__init__.py``
  files.

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 :class:`django.core.signing.Signer` algorithm 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``.

* 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.

.. _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``.

* The passing of URL kwargs directly to the context by
  :class:`~django.views.generic.base.TemplateView` is deprecated. Reference
  them in the template with ``view.kwargs`` instead.

* 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>`.

.. _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.
<commit_msg>Refs #12990 -- Added example to JSONField release notes.<commit_after>============================================
Django 3.1 release notes - UNDER DEVELOPMENT
============================================

*Expected August 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, and 3.8. 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>`.

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>`.

* ``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, Kyrgyz, and Tajik
  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.

Migrations
~~~~~~~~~~

* Migrations are now loaded also from directories without ``__init__.py``
  files.

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 :class:`django.core.signing.Signer` algorithm 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``.

* 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.

.. _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``.

* The passing of URL kwargs directly to the context by
  :class:`~django.views.generic.base.TemplateView` is deprecated. Reference
  them in the template with ``view.kwargs`` instead.

* 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>`.

.. _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.

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