============================================
Django 4.2 release notes - UNDER DEVELOPMENT
============================================

*Expected April 2023*

Welcome to Django 4.2!

These release notes cover the :ref:`new features <whats-new-4.2>`, as well as
some :ref:`backwards incompatible changes <backwards-incompatible-4.2>` you'll
want to be aware of when upgrading from Django 4.1 or earlier. We've
:ref:`begun the deprecation process for some features
<deprecated-features-4.2>`.

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

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

Django 4.2 supports Python 3.8, 3.9, 3.10, and 3.11. We **highly recommend**
and only officially support the latest release of each series.

.. _whats-new-4.2:

What's new in Django 4.2
========================

Psycopg 3 support
-----------------

Django now supports `psycopg`_ version 3.1.8 or higher. To update your code,
install the `psycopg library`_, you don't need to change the
:setting:`ENGINE <DATABASE-ENGINE>` as ``django.db.backends.postgresql``
supports both libraries.

Support for ``psycopg2`` is likely to be deprecated and removed at some point
in the future.

.. _psycopg: https://www.psycopg.org/psycopg3/
.. _psycopg library: https://pypi.org/project/psycopg/

Comments on columns and tables
------------------------------

The new :attr:`Field.db_comment <django.db.models.Field.db_comment>` and
:attr:`Meta.db_table_comment <django.db.models.Options.db_table_comment>`
options allow creating comments on columns and tables, respectively. For
example::

    from django.db import models

    class Question(models.Model):
        text = models.TextField(db_comment="Poll question")
        pub_date = models.DateTimeField(
            db_comment="Date and time when the question was published",
        )

        class Meta:
            db_table_comment = "Poll questions"


    class Answer(models.Model):
        question = models.ForeignKey(
            Question,
            on_delete=models.CASCADE,
            db_comment="Reference to a question",
        )
        answer = models.TextField(db_comment="Question answer")

        class Meta:
            db_table_comment = "Question answers"

Also, the new :class:`~django.db.migrations.operations.AlterModelTableComment`
operation allows changing table comments defined in the
:attr:`Meta.db_table_comment <django.db.models.Options.db_table_comment>`.

Mitigation for the BREACH attack
--------------------------------

:class:`~django.middleware.gzip.GZipMiddleware` now includes a mitigation for
the BREACH attack. It will add up to 100 random bytes to gzip responses to make
BREACH attacks harder. Read more about the mitigation technique in the `Heal
The Breach (HTB) paper`_.

.. _Heal The Breach (HTB) paper: https://ieeexplore.ieee.org/document/9754554

In-memory file storage
----------------------

The new :class:`django.core.files.storage.InMemoryStorage` class provides a
non-persistent storage useful for speeding up tests by avoiding disk access.

Custom file storages
--------------------

The new :setting:`STORAGES` setting allows configuring multiple custom file
storage backends. It also controls storage engines for managing
:doc:`files </topics/files>` (the ``"defaut"`` key) and :doc:`static files
</ref/contrib/staticfiles>` (the ``"staticfiles"`` key).

The old ``DEFAULT_FILE_STORAGE`` and ``STATICFILES_STORAGE`` settings are
deprecated as of this release.

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

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

* The light or dark color theme of the admin can now be toggled in the UI, as
  well as being set to follow the system setting.

* The admin's font stack now prefers system UI fonts and no longer requires
  downloading fonts. Additionally, CSS variables are available to more easily
  override the default font families.

* The :source:`admin/delete_confirmation.html
  <django/contrib/admin/templates/admin/delete_confirmation.html>` template now
  has some additional blocks and scripting hooks to ease customization.

* The chosen options of
  :attr:`~django.contrib.admin.ModelAdmin.filter_horizontal` and
  :attr:`~django.contrib.admin.ModelAdmin.filter_vertical` widgets are now
  filterable.

* The ``admin/base.html`` template now has a new block ``nav-breadcrumbs``
  which contains the navigation landmark and the ``breadcrumbs`` block.

* :attr:`.ModelAdmin.list_editable` now uses atomic transactions when making
  edits.

* jQuery is upgraded from version 3.6.0 to 3.6.3.

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

* The default iteration count for the PBKDF2 password hasher is increased from
  390,000 to 480,000.

* :class:`~django.contrib.auth.forms.UserCreationForm` now saves many-to-many
  form fields for a custom user model.

* The new :class:`~django.contrib.auth.forms.BaseUserCreationForm` is now the
  recommended base class for customizing the user creation form.

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

* The :doc:`GeoJSON serializer </ref/contrib/gis/serializers>` now outputs the
  ``id`` key for serialized features, which defaults to the primary key of
  objects.

* The :class:`~django.contrib.gis.gdal.GDALRaster` class now supports
  :class:`pathlib.Path`.

* The :class:`~django.contrib.gis.geoip2.GeoIP2` class now supports  ``.mmdb``
  files downloaded from DB-IP.

* The OpenLayers template widget no longer includes inline CSS (which also
  removes the former ``map_css`` block) to better comply with a strict Content
  Security Policy.

* :class:`~django.contrib.gis.forms.widgets.OpenLayersWidget` is now based on
  OpenLayers 7.2.2 (previously 4.6.5).

* The new :lookup:`isempty` lookup and
  :class:`IsEmpty() <django.contrib.gis.db.models.functions.IsEmpty>`
  expression allow filtering empty geometries on PostGIS.

* The new :class:`FromWKB() <django.contrib.gis.db.models.functions.FromWKB>`
  and :class:`FromWKT() <django.contrib.gis.db.models.functions.FromWKT>`
  functions allow creating geometries from Well-known binary (WKB) and
  Well-known text (WKT) representations.

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

* The new :lookup:`trigram_strict_word_similar` lookup, and the
  :class:`TrigramStrictWordSimilarity()
  <django.contrib.postgres.search.TrigramStrictWordSimilarity>` and
  :class:`TrigramStrictWordDistance()
  <django.contrib.postgres.search.TrigramStrictWordDistance>` expressions allow
  using trigram strict word similarity.

* The :lookup:`arrayfield.overlap` lookup now supports ``QuerySet.values()``
  and ``values_list()`` as a right-hand side.

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

* The new :meth:`.Sitemap.get_languages_for_item` method allows customizing the
  list of languages for which the item is displayed.

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

* :class:`~django.contrib.staticfiles.storage.ManifestStaticFilesStorage` now
  replaces paths to JavaScript modules in ``import`` and ``export`` statements
  with their hashed counterparts.

* The new :attr:`.ManifestStaticFilesStorage.manifest_hash` attribute provides
  a hash over all files in the manifest and changes whenever one of the files
  changes.

Database backends
~~~~~~~~~~~~~~~~~

* The new ``"assume_role"`` option is now supported in :setting:`OPTIONS` on
  PostgreSQL to allow specifying the :ref:`session role <database-role>`.

* The new ``"server_side_binding"`` option is now supported in
  :setting:`OPTIONS` on PostgreSQL with ``psycopg`` 3.1.8+ to allow using
  :ref:`server-side binding cursors <database-server-side-parameters-binding>`.

Decorators
~~~~~~~~~~

* ...

Email
~~~~~

* ...

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

* The debug page now shows :pep:`exception notes <678>` and
  :pep:`fine-grained error locations <657>` on Python 3.11+.

Forms
~~~~~

* :class:`~django.forms.ModelForm` now accepts the new ``Meta`` option
  ``formfield_callback`` to customize form fields.

* :func:`~django.forms.models.modelform_factory` now respects the
  ``formfield_callback`` attribute of the ``form``’s ``Meta``.

* Session cookies are now treated as credentials and therefore hidden and
  replaced with stars (``**********``) in error reports.

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

* Added support and translations for the Central Kurdish (Sorani) language.

* The :class:`~django.middleware.locale.LocaleMiddleware` now respects a
  language from the request when :func:`~django.conf.urls.i18n.i18n_patterns`
  is used with the ``prefix_default_language`` argument set to ``False``.

Logging
~~~~~~~

* The :ref:`django-db-logger` logger now logs transaction management queries
  (``BEGIN``, ``COMMIT``, and ``ROLLBACK``) at the ``DEBUG`` level.

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

* :djadmin:`makemessages` command now supports locales with private sub-tags
  such as ``nl_NL-x-informal``.

* The new :option:`makemigrations --update` option merges model changes into
  the latest migration and optimizes the resulting operations.

Migrations
~~~~~~~~~~

* Migrations now support serialization of ``enum.Flag`` objects.

Models
~~~~~~

* ``QuerySet`` now extensively supports filtering against
  :ref:`window-functions` with the exception of disjunctive filter lookups
  against window functions when performing aggregation.

* :meth:`~.QuerySet.prefetch_related` now supports
  :class:`~django.db.models.Prefetch` objects with sliced querysets.

* :ref:`Registering lookups <lookup-registration-api>` on
  :class:`~django.db.models.Field` instances is now supported.

* The new ``robust`` argument for :func:`~django.db.transaction.on_commit`
  allows performing actions that can fail after a database transaction is
  successfully committed.

* The new :class:`KT() <django.db.models.fields.json.KT>` expression represents
  the text value of a key, index, or path transform of
  :class:`~django.db.models.JSONField`.

* :class:`~django.db.models.functions.Now` now supports microsecond precision
  on MySQL and millisecond precision on SQLite.

* :class:`F() <django.db.models.F>` expressions that output ``BooleanField``
  can now be negated using ``~F()`` (inversion operator).

* ``Model`` now provides asynchronous versions of some methods that use the
  database, using an ``a`` prefix: :meth:`~.Model.adelete`,
  :meth:`~.Model.arefresh_from_db`, and :meth:`~.Model.asave`.

* Related managers now provide asynchronous versions of methods that change a
  set of related objects, using an ``a`` prefix: :meth:`~.RelatedManager.aadd`,
  :meth:`~.RelatedManager.aclear`, :meth:`~.RelatedManager.aremove`, and
  :meth:`~.RelatedManager.aset`.

* :attr:`CharField.max_length <django.db.models.CharField.max_length>` is no
  longer required to be set on PostgreSQL, which supports unlimited ``VARCHAR``
  columns.

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

* :class:`~django.http.StreamingHttpResponse` now supports async iterators
  when Django is served via ASGI.

Tests
~~~~~

* The :option:`test --debug-sql` option now formats SQL queries with
  ``sqlparse``.

* The :class:`~django.test.RequestFactory`,
  :class:`~django.test.AsyncRequestFactory`, :class:`~django.test.Client`, and
  :class:`~django.test.AsyncClient` classes now support the ``headers``
  parameter, which accepts a dictionary of header names and values. This allows
  a more natural syntax for declaring headers.

  .. code-block:: python

     # Before:
     self.client.get("/home/", HTTP_ACCEPT_LANGUAGE="fr")
     await self.async_client.get("/home/", ACCEPT_LANGUAGE="fr")

     # After:
     self.client.get("/home/", headers={"accept-language": "fr"})
     await self.async_client.get("/home/", headers={"accept-language": "fr"})

Utilities
~~~~~~~~~

* The new ``encoder`` parameter for :meth:`django.utils.html.json_script`
  function allows customizing a JSON encoder class.

* The private internal vendored copy of ``urllib.parse.urlsplit()`` now strips
  ``'\r'``, ``'\n'``, and ``'\t'`` (see :cve:`2022-0391` and :bpo:`43882`).
  This is to protect projects that may be incorrectly using the internal
  ``url_has_allowed_host_and_scheme()`` function, instead of using one of the
  documented functions for handling URL redirects. The Django functions were
  not affected.

* The new :func:`django.utils.http.content_disposition_header` function returns
  a ``Content-Disposition`` HTTP header value as specified by :rfc:`6266`.

Validators
~~~~~~~~~~

* The list of common passwords used by ``CommonPasswordValidator`` is updated
  to the most recent version.

.. _backwards-incompatible-4.2:

Backwards incompatible changes in 4.2
=====================================

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

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

* ``DatabaseFeatures.allows_group_by_pk`` is removed as it only remained to
  accommodate a MySQL extension that has been supplanted by proper functional
  dependency detection in MySQL 5.7.15. Note that
  ``DatabaseFeatures.allows_group_by_selected_pks`` is still supported and
  should be enabled if your backend supports functional dependency detection in
  ``GROUP BY`` clauses as specified by the ``SQL:1999`` standard.

Dropped support for MariaDB 10.3
--------------------------------

Upstream support for MariaDB 10.3 ends in May 2023. Django 4.2 supports MariaDB
10.4 and higher.

Dropped support for MySQL 5.7
-----------------------------

Upstream support for MySQL 5.7 ends in October 2023. Django 4.2 supports MySQL
8 and higher.

Dropped support for PostgreSQL 11
---------------------------------

Upstream support for PostgreSQL 11 ends in November 2023. Django 4.2 supports
PostgreSQL 12 and higher.

Setting ``update_fields`` in ``Model.save()`` may now be required
-----------------------------------------------------------------

In order to avoid updating unnecessary columns,
:meth:`.QuerySet.update_or_create` now passes ``update_fields`` to the
:meth:`Model.save() <django.db.models.Model.save>` calls. As a consequence, any
fields modified in the custom ``save()`` methods should be added to the
``update_fields`` keyword argument before calling ``super()``. See
:ref:`overriding-model-methods` for more details.

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

* The undocumented ``SimpleTemplateResponse.rendering_attrs`` and
  ``TemplateResponse.rendering_attrs`` are renamed to ``non_picklable_attrs``.

* The undocumented ``django.http.multipartparser.parse_header()`` function is
  removed. Use ``django.utils.http.parse_header_parameters()`` instead.

* :ttag:`{% blocktranslate asvar … %}<blocktranslate>` result is now marked as
  safe for (HTML) output purposes.

* The ``autofocus`` HTML attribute in the admin search box is removed as it can
  be confusing for screen readers.

* The :option:`makemigrations --check` option no longer creates missing
  migration files.

* The ``alias`` argument for :meth:`.Expression.get_group_by_cols` is removed.

* The minimum supported version of ``sqlparse`` is increased from 0.2.2 to
  0.3.1.

* The undocumented ``negated`` parameter of the
  :class:`~django.db.models.Exists` expression is removed.

* The ``is_summary`` argument of the undocumented ``Query.add_annotation()``
  method is removed.

* The minimum supported version of SQLite is increased from 3.9.0 to 3.21.0.

* :djadmin:`inspectdb` now uses ``display_size`` from
  ``DatabaseIntrospection.get_table_description()`` rather than
  ``internal_size`` for ``CharField``.

* The minimum supported version of ``asgiref`` is increased from 3.5.2 to
  3.6.0.

* :class:`~django.contrib.auth.forms.UserCreationForm` now rejects usernames
  that differ only in case. If you need the previous behavior, use
  :class:`~django.contrib.auth.forms.BaseUserCreationForm` instead.

* The minimum supported version of ``mysqlclient`` is increased from 1.4.0 to
  1.4.3.

* The minimum supported version of ``argon2-cffi`` is increased  from 19.1.0 to
  19.2.0.

* The minimum supported version of ``Pillow`` is increased from 6.2.0 to 6.2.1.

* The minimum supported version of ``jinja2`` is increased from 2.9.2 to
  2.11.0.

* The minimum supported version of `redis-py`_ is increased from 3.0.0 to
  3.4.0.

* Manually instantiated ``WSGIRequest`` objects must be provided a file-like
  object for ``wsgi.input``. Previously, Django was more lax than the expected
  behavior as specified by the WSGI specification.

* Support for ``PROJ`` < 5 is removed.

.. _`redis-py`: https://pypi.org/project/redis/

.. _deprecated-features-4.2:

Features deprecated in 4.2
==========================

``index_together`` option is deprecated in favor of ``indexes``
---------------------------------------------------------------

The :attr:`Meta.index_together <django.db.models.Options.index_together>`
option is deprecated in favor of the :attr:`~django.db.models.Options.indexes`
option.

Migrating existing ``index_together`` should be handled as a migration. For
example::

    class Author(models.Model):
        rank = models.IntegerField()
        name = models.CharField(max_length=30)

        class Meta:
            index_together = [["rank", "name"]]

Should become::

    class Author(models.Model):
        rank = models.IntegerField()
        name = models.CharField(max_length=30)

        class Meta:
            indexes = [models.Index(fields=["rank", "name"])]

Running the :djadmin:`makemigrations` command will generate a migration
containing a :class:`~django.db.migrations.operations.RenameIndex` operation
which will rename the existing index.

The ``AlterIndexTogether`` migration operation is now officially supported only
for pre-Django 4.2 migration files. For backward compatibility reasons, it's
still part of the public API, and there's no plan to deprecate or remove it,
but it should not be used for new migrations. Use
:class:`~django.db.migrations.operations.AddIndex` and
:class:`~django.db.migrations.operations.RemoveIndex` operations instead.

Passing encoded JSON string literals to ``JSONField`` is deprecated
-------------------------------------------------------------------

``JSONField`` and its associated lookups and aggregates used to allow passing
JSON encoded string literals which caused ambiguity on whether string literals
were already encoded from database backend's perspective.

During the deprecation period string literals will be attempted to be JSON
decoded and a warning will be emitted on success that points at passing
non-encoded forms instead.

Code that use to pass JSON encoded string literals::

    Document.objects.bulk_create(
        Document(data=Value("null")),
        Document(data=Value("[]")),
        Document(data=Value('"foo-bar"')),
    )
    Document.objects.annotate(
        JSONBAgg("field", default=Value('[]')),
    )

Should become::

    Document.objects.bulk_create(
        Document(data=Value(None, JSONField())),
        Document(data=[]),
        Document(data="foo-bar"),
    )
    Document.objects.annotate(
        JSONBAgg("field", default=[]),
    )

From Django 5.1+ string literals will be implicitly interpreted as JSON string
literals.

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

* The ``BaseUserManager.make_random_password()`` method is deprecated. See
  `recipes and best practices
  <https://docs.python.org/3/library/secrets.html#recipes-and-best-practices>`_
  for using Python's :py:mod:`secrets` module to generate passwords.

* The ``length_is`` template filter is deprecated in favor of :tfilter:`length`
  and the ``==`` operator within an :ttag:`{% if %}<if>` tag. For example

  .. code-block:: html+django

    {% if value|length == 4 %}…{% endif %}
    {% if value|length == 4 %}True{% else %}False{% endif %}

  instead of:

  .. code-block:: html+django

    {% if value|length_is:4 %}…{% endif %}
    {{ value|length_is:4 }}

* ``django.contrib.auth.hashers.SHA1PasswordHasher``,
  ``django.contrib.auth.hashers.UnsaltedSHA1PasswordHasher``, and
  ``django.contrib.auth.hashers.UnsaltedMD5PasswordHasher`` are deprecated.

* ``django.contrib.postgres.fields.CICharField`` is deprecated in favor of
  ``CharField(db_collation="…")`` with a case-insensitive non-deterministic
  collation.

* ``django.contrib.postgres.fields.CIEmailField`` is deprecated in favor of
  ``EmailField(db_collation="…")`` with a case-insensitive non-deterministic
  collation.

* ``django.contrib.postgres.fields.CITextField`` is deprecated in favor of
  ``TextField(db_collation="…")`` with a case-insensitive non-deterministic
  collation.

* ``django.contrib.postgres.fields.CIText`` mixin is deprecated.

* The ``map_height`` and ``map_width`` attributes of ``BaseGeometryWidget`` are
  deprecated, use CSS to size map widgets instead.

* ``SimpleTestCase.assertFormsetError()`` is deprecated in favor of
  ``assertFormSetError()``.

* ``TransactionTestCase.assertQuerysetEqual()`` is deprecated in favor of
  ``assertQuerySetEqual()``.

* Passing positional arguments to ``Signer`` and ``TimestampSigner`` is
  deprecated in favor of keyword-only arguments.

* The ``DEFAULT_FILE_STORAGE`` setting is deprecated in favor of
  ``STORAGES["default"]``.

* The ``STATICFILES_STORAGE`` setting is deprecated in favor of
  ``STORAGES["staticfiles"]``.

* The ``django.core.files.storage.get_storage_class()`` function is deprecated.
