============================================
Django 4.0 release notes - UNDER DEVELOPMENT
============================================

*Expected December 2021*

Welcome to Django 4.0!

These release notes cover the :ref:`new features <whats-new-4.0>`, as well as
some :ref:`backwards incompatible changes <backwards-incompatible-4.0>` you'll
want to be aware of when upgrading from Django 3.2 or earlier. We've
:ref:`begun the deprecation process for some features
<deprecated-features-4.0>`.

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

Python compatibility
====================

Django 4.0 supports Python 3.8, 3.9, and 3.10. We **highly recommend** and only
officially support the latest release of each series.

The Django 3.2.x series is the last to support Python 3.6 and 3.7.

.. _whats-new-4.0:

What's new in Django 4.0
========================

Functional unique constraints
-----------------------------

The new :attr:`*expressions <django.db.models.UniqueConstraint.expressions>`
positional argument of
:class:`UniqueConstraint() <django.db.models.UniqueConstraint>` enables
creating functional unique constraints on expressions and database functions.
For example::

    from django.db import models
    from django.db.models import UniqueConstraint
    from django.db.models.functions import Lower


    class MyModel(models.Model):
        first_name = models.CharField(max_length=255)
        last_name = models.CharField(max_length=255)

        class Meta:
            indexes = [
                UniqueConstraint(
                    Lower('first_name'),
                    Lower('last_name').desc(),
                    name='first_last_name_unique',
                ),
            ]

Functional unique constraints are added to models using the
:attr:`Meta.constraints <django.db.models.Options.constraints>` option.

Minor features
--------------

:mod:`django.contrib.admin`
~~~~~~~~~~~~~~~~~~~~~~~~~~~

* The ``admin/base.html`` template now has a new block ``header`` which
  contains the admin site header.

* The new :meth:`.ModelAdmin.get_formset_kwargs` method allows customizing the
  keyword arguments passed to the constructor of a formset.

:mod:`django.contrib.admindocs`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* The admindocs now allows esoteric setups where :setting:`ROOT_URLCONF` is not
  a string.

* The model section of the ``admindocs`` now shows cached properties.

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

* The default iteration count for the PBKDF2 password hasher is increased from
  260,000 to 320,000.

* The new
  :attr:`LoginView.next_page <django.contrib.auth.views.LoginView.next_page>`
  attribute and
  :meth:`~django.contrib.auth.views.LoginView.get_default_redirect_url` method
  allow customizing the redirect after login.

:mod:`django.contrib.contenttypes`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* ...

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

* ...

:mod:`django.contrib.messages`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* ...

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

* The PostgreSQL backend now supports connecting by a service name. See
  :ref:`postgresql-connection-settings` for more details.

:mod:`django.contrib.redirects`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* ...

:mod:`django.contrib.sessions`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* ...

:mod:`django.contrib.sitemaps`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* ...

:mod:`django.contrib.sites`
~~~~~~~~~~~~~~~~~~~~~~~~~~~

* ...

:mod:`django.contrib.staticfiles`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* ...

:mod:`django.contrib.syndication`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* ...

Cache
~~~~~

* ...

CSRF
~~~~

* ...

Decorators
~~~~~~~~~~

* ...

Email
~~~~~

* ...

Error Reporting
~~~~~~~~~~~~~~~

* ...

File Storage
~~~~~~~~~~~~

* ...

File Uploads
~~~~~~~~~~~~

* ...

Forms
~~~~~

* :class:`~django.forms.ModelChoiceField` now includes the provided value in
  the ``params`` argument of a raised
  :exc:`~django.core.exceptions.ValidationError` for the ``invalid_choice``
  error message. This allows custom error messages to use the ``%(value)s``
  placeholder.

Generic Views
~~~~~~~~~~~~~

* ...

Internationalization
~~~~~~~~~~~~~~~~~~~~

* ...

Logging
~~~~~~~

* ...

Management Commands
~~~~~~~~~~~~~~~~~~~

* The :djadmin:`runserver` management command now supports the
  :option:`--skip-checks` option.

* On PostgreSQL, :djadmin:`dbshell` now supports specifying a password file.

Migrations
~~~~~~~~~~

* ...

Models
~~~~~~

* New :meth:`QuerySet.contains(obj) <.QuerySet.contains>` method returns
  whether the queryset contains the given object. This tries to perform the
  query in the simplest and fastest way possible.

Requests and Responses
~~~~~~~~~~~~~~~~~~~~~~

* ...

Security
~~~~~~~~

* ...

Serialization
~~~~~~~~~~~~~

* ...

Signals
~~~~~~~

* The new ``stdout`` argument for :func:`~django.db.models.signals.pre_migrate`
  and :func:`~django.db.models.signals.post_migrate` signals allows redirecting
  output to a stream-like object. It should be preferred over
  :py:data:`sys.stdout` and :py:func:`print` when emitting verbose output in
  order to allow proper capture when testing.

Templates
~~~~~~~~~

* ...

Tests
~~~~~

* The new ``serialized_aliases`` argument of
  :func:`django.test.utils.setup_databases` determines which
  :setting:`DATABASES` aliases test databases should have their state
  serialized to allow usage of the
  :ref:`serialized_rollback <test-case-serialized-rollback>` feature.

URLs
~~~~

* ...

Utilities
~~~~~~~~~

* ...

Validators
~~~~~~~~~~

* ...

.. _backwards-incompatible-4.0:

Backwards incompatible changes in 4.0
=====================================

Database backend API
--------------------

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

* ...

:mod:`django.contrib.gis`
-------------------------

* Support for PostGIS 2.3 is removed.

Dropped support for PostgreSQL 9.6
----------------------------------

Upstream support for PostgreSQL 9.6 ends in November 2021. Django 4.0 supports
PostgreSQL 10 and higher.

Dropped support for Oracle 12.2 and 18c
---------------------------------------

Upstream support for Oracle 12.2 ends in March 2022 and for Oracle 18c it ends
in June 2021. Django 3.2 will be supported until April 2024. Django 4.0
officially supports Oracle 19c.

Miscellaneous
-------------

* Support for ``cx_Oracle`` < 7.0 is removed.

* To allow serving a Django site on a subpath without changing the value of
  :setting:`STATIC_URL`, the leading slash is removed from that setting (now
  ``'static/'``) in the default :djadmin:`startproject` template.

* The :class:`~django.contrib.admin.AdminSite` method for the admin ``index``
  view is no longer decorated with ``never_cache`` when accessed directly,
  rather than via the recommended ``AdminSite.urls`` property, or
  ``AdminSite.get_urls()`` method.

* Unsupported operations on a sliced queryset now raise ``TypeError`` instead
  of ``AssertionError``.

.. _deprecated-features-4.0:

Features deprecated in 4.0
==========================

Miscellaneous
-------------

* ``SERIALIZE`` test setting is deprecated as it can be inferred from the
  :attr:`~django.test.TestCase.databases` with the
  :ref:`serialized_rollback <test-case-serialized-rollback>` option enabled.

Features removed in 4.0
=======================

These features have reached the end of their deprecation cycle and are removed
in Django 4.0.

See :ref:`deprecated-features-3.0` for details on these changes, including how
to remove usage of these features.

* ``django.utils.http.urlquote()``, ``urlquote_plus()``, ``urlunquote()``, and
  ``urlunquote_plus()`` are removed.

* ``django.utils.encoding.force_text()`` and ``smart_text()`` are removed.

* ``django.utils.translation.ugettext()``, ``ugettext_lazy()``,
  ``ugettext_noop()``, ``ungettext()``, and ``ungettext_lazy()`` are removed.

* ``django.views.i18n.set_language()`` doesn't set the user language in
  ``request.session`` (key ``_language``).

* ``alias=None`` is required in the signature of
  ``django.db.models.Expression.get_group_by_cols()`` subclasses.

* ``django.utils.text.unescape_entities()`` is removed.

* ``django.utils.http.is_safe_url()`` is removed.

See :ref:`deprecated-features-3.1` for details on these changes, including how
to remove usage of these features.

* The ``PASSWORD_RESET_TIMEOUT_DAYS`` setting is removed.

* The :lookup:`isnull` lookup no longer allows using non-boolean values as the
  right-hand side.

* The ``django.db.models.query_utils.InvalidQuery`` exception class is removed.

* The ``django-admin.py`` entry point is removed.

* The ``HttpRequest.is_ajax()`` method is removed.

* Support for the pre-Django 3.1 encoding format of cookies values used by
  ``django.contrib.messages.storage.cookie.CookieStorage`` is removed.

* Support for the pre-Django 3.1 password reset tokens in the admin site (that
  use the SHA-1 hashing algorithm) is removed.

* Support for the pre-Django 3.1 encoding format of sessions is removed.

* Support for the pre-Django 3.1 ``django.core.signing.Signer`` signatures
  (encoded with the SHA-1 algorithm) is removed.

* Support for the pre-Django 3.1 ``django.core.signing.dumps()`` signatures
  (encoded with the SHA-1 algorithm) in ``django.core.signing.loads()`` is
  removed.

* Support for the pre-Django 3.1 user sessions (that use the SHA-1 algorithm)
  is removed.

* The ``get_request`` argument for
  ``django.utils.deprecation.MiddlewareMixin.__init__()`` is required and
  doesn't accept ``None``.

* The ``providing_args`` argument for ``django.dispatch.Signal`` is removed.

* The ``length`` argument for ``django.utils.crypto.get_random_string()`` is
  required.

* The ``list`` message for ``ModelMultipleChoiceField`` is removed.

* Support for passing raw column aliases to ``QuerySet.order_by()`` is removed.

* The ``NullBooleanField`` model field is removed, except for support in
  historical migrations.

* ``django.conf.urls.url()`` is removed.

* The ``django.contrib.postgres.fields.JSONField`` model field is removed,
  except for support in historical migrations.

* ``django.contrib.postgres.fields.jsonb.KeyTransform`` and
  ``django.contrib.postgres.fields.jsonb.KeyTextTransform`` are removed.

* ``django.contrib.postgres.forms.JSONField`` is removed.

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

* The ``DEFAULT_HASHING_ALGORITHM`` transitional setting is removed.
