2.0.txt

============================================
Django 2.0 release notes - UNDER DEVELOPMENT
============================================

Welcome to Django 2.0!

These release notes cover the :ref:`new features <whats-new-2.0>`, as well as
some :ref:`backwards incompatible changes <backwards-incompatible-2.0>` you'll
want to be aware of when upgrading from Django 1.11 or earlier. We've
:ref:`dropped some features<removed-features-2.0>` that have reached the end of
their deprecation cycle, and we've :ref:`begun the deprecation process for some
features <deprecated-features-2.0>`.

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

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

Django 2.0 supports Python 3.5+. Since Django 1.11, support for Python 2.7 and
3.4 is removed. We **highly recommend** and only officially support the latest
release of each series.

Third-party library support for older version of Django
=======================================================

Following the release of Django 2.0, we suggest that third-party app authors
drop support for all versions of Django prior to 1.11. At that time, you should
be able run your package's tests using ``python -Wd`` so that deprecation
warnings do appear. After making the deprecation warning fixes, your app should
be compatible with Django 2.0.

.. _whats-new-2.0:

What's new in Django 2.0
========================

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

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

* ...

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

* ...

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

* The default iteration count for the PBKDF2 password hasher is increased from
  36,000 to 100,000.

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

* ...

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

* Added MySQL support for the
  :class:`~django.contrib.gis.db.models.functions.AsGeoJSON` function,
  :class:`~django.contrib.gis.db.models.functions.GeoHash` function,
  :class:`~django.contrib.gis.db.models.functions.IsValid` function, and
  :lookup:`isvalid` lookup.

* Added the :class:`~django.contrib.gis.db.models.functions.Azimuth` and
  :class:`~django.contrib.gis.db.models.functions.LineLocatePoint` functions,
  supported on PostGIS and SpatiaLite.

* Any :class:`~django.contrib.gis.geos.GEOSGeometry` imported from GeoJSON now
  has its SRID set.

* Added the :attr:`.OSMWidget.default_zoom` attribute to customize the map's
  default zoom level.

* Made metadata readable and editable on rasters through the
  :attr:`~django.contrib.gis.gdal.GDALRaster.metadata`,
  :attr:`~django.contrib.gis.gdal.GDALRaster.info`, and
  :attr:`~django.contrib.gis.gdal.GDALBand.metadata` attributes.

* Allowed passing driver-specific creation options to
  :class:`~django.contrib.gis.gdal.GDALRaster` objects using ``papsz_options``.

* Allowed creating :class:`~django.contrib.gis.gdal.GDALRaster` objects in
  GDAL's internal virtual filesystem. Rasters can now be :ref:`created from and
  converted to binary data <gdal-raster-vsimem>` in-memory.

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

* ...

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

* The new ``distinct`` argument for
  :class:`~django.contrib.postgres.aggregates.ArrayAgg` determines if
  concatenated values will be distinct.

* The new :class:`~django.contrib.postgres.functions.RandomUUID` database
  function returns a version 4 UUID. It requires use of PostgreSQL's
  ``pgcrypto`` extension which can be activated using the new
  :class:`~django.contrib.postgres.operations.CryptoExtension` migration
  operation.

* :class:`django.contrib.postgres.indexes.GinIndex` now supports the
  ``fast_update`` and ``gin_pending_list_limit`` parameters.

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

* ...

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

* ...

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

* Added the ``protocol`` keyword argument to the
  :class:`~django.contrib.sitemaps.GenericSitemap` constructor.

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

* ...

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

* ...

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

* ...

Cache
~~~~~

* ...

CSRF
~~~~

* ...

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

* ...

Email
~~~~~

* ...

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

* :meth:`File.open() <django.core.files.File.open>` can be used as a context
  manager, e.g. ``with file.open() as f:``.

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

* ...

Forms
~~~~~

* The new ``date_attrs`` and ``time_attrs`` arguments for
  :class:`~django.forms.SplitDateTimeWidget` and
  :class:`~django.forms.SplitHiddenDateTimeWidget` allow specifying different
  HTML attributes for the ``DateInput`` and ``TimeInput`` (or hidden)
  subwidgets.

* The new :meth:`Form.errors.get_json_data()
  <django.forms.Form.errors.get_json_data>` method returns form errors as
  a dictionary suitable for including in a JSON response.

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

* The new :attr:`.ContextMixin.extra_context` attribute allows adding context
  in ``View.as_view()``.

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

* ...

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

* :djadmin:`inspectdb` now translates MySQL's unsigned integer columns to
  ``PositiveIntegerField`` or ``PositiveSmallIntegerField``.

* The new :option:`makemessages --add-location` option controls the comment
  format in PO files.

* :djadmin:`loaddata` can now :ref:`read from stdin <loading-fixtures-stdin>`.

* The new :option:`diffsettings --output` option allows formatting the output
  in a unified diff format.

* On Oracle, :djadmin:`inspectdb` can now introspect ``AutoField`` if the
  column is created as an identity column.

* On MySQL, :djadmin:`dbshell` now supports client-side TLS certificates.

Migrations
~~~~~~~~~~

* ...

Models
~~~~~~

* The new :class:`~django.db.models.functions.StrIndex` database function
  finds the starting index of a string inside another string.

* On Oracle, ``AutoField`` and ``BigAutoField`` are now created as `identity
  columns`_.

  .. _`identity columns`: https://docs.oracle.com/database/121/DRDAA/migr_tools_feat.htm#DRDAA109

* The new ``chunk_size`` parameter of :meth:`.QuerySet.iterator` controls the
  number of rows fetched by the Python database client when streaming results
  from the database. For databases that don't support server-side cursors, it
  controls the number of results Django fetches from the database adapter.

* Added the :class:`~django.db.models.functions.datetime.ExtractQuarter`
  function to extract the quarter from :class:`~django.db.models.DateField` and
  :class:`~django.db.models.DateTimeField`, and exposed it through the
  :lookup:`quarter` lookup.

* Added the :class:`~django.db.models.functions.datetime.TruncQuarter`
  function to truncate :class:`~django.db.models.DateField` and
  :class:`~django.db.models.DateTimeField` to the first day of a quarter.

* Added the :attr:`~django.db.models.Index.db_tablespace` parameter to
  class-based indexes.

* If the database supports a native duration field (Oracle and PostgreSQL),
  :class:`~django.db.models.functions.datetime.Extract` now works with
  :class:`~django.db.models.DurationField`.

* Added the ``of`` argument to :meth:`.QuerySet.select_for_update()`, supported
  on PostgreSQL and Oracle, to lock only rows from specific tables rather than
  all selected tables. It may be helpful particularly when
  :meth:`~.QuerySet.select_for_update()` is used in conjunction with
  :meth:`~.QuerySet.select_related()`.

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

* The :djadmin:`runserver` Web server supports HTTP 1.1.

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

* ...

Signals
~~~~~~~

* ...

Templates
~~~~~~~~~

* To increase the usefulness of :meth:`.Engine.get_default` in third-party
  apps, it now returns the first engine if multiple ``DjangoTemplates`` engines
  are configured in ``TEMPLATES`` rather than raising ``ImproperlyConfigured``.

* Custom template tags may now accept keyword-only arguments.

Tests
~~~~~

* Added threading support to :class:`~django.test.LiveServerTestCase`.

* Added settings that allow customizing the test tablespace parameters for
  Oracle: :setting:`DATAFILE_SIZE`, :setting:`DATAFILE_TMP_SIZE`,
  :setting:`DATAFILE_EXTSIZE`, and :setting:`DATAFILE_TMP_EXTSIZE`.

URLs
~~~~

* ...

Validators
~~~~~~~~~~

* ...

.. _backwards-incompatible-2.0:

Backwards incompatible changes in 2.0
=====================================

Removed support for bytestrings in some places
----------------------------------------------

To support native Python 2 strings, older Django versions had to accept both
bytestrings and unicode strings. Now that Python 2 support is dropped,
bytestrings should only be encountered around input/output boundaries (handling
of binary fields or HTTP streams, for example). You might have to update your
code to limit bytestring usage to a minimum, as Django no longer accepts
bytestrings in certain code paths.

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

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

* The ``DatabaseOperations.datetime_cast_date_sql()``,
  ``datetime_cast_time_sql()``, ``datetime_trunc_sql()``,
  ``datetime_extract_sql()``, and ``date_interval_sql()`` methods now return
  only the SQL to perform the operation instead of SQL and a list of
  parameters.

* Third-party database backends should add a ``DatabaseWrapper.display_name``
  attribute with the name of the database that your backend works with. Django
  may use it in various messages, such as in system checks.

* The first argument of ``SchemaEditor._alter_column_type_sql()`` is now
  ``model`` rather than ``table``.

* The first argument of ``SchemaEditor._create_index_name()`` is now
  ``table_name`` rather than ``model``.

* To enable ``FOR UPDATE OF`` support, set
  ``DatabaseFeatures.has_select_for_update_of = True``. If the database
  requires that the arguments to ``OF`` be columns rather than tables, set
  ``DatabaseFeatures.select_for_update_of_column = True``.

Dropped support for Oracle 11.2
-------------------------------

The end of upstream support for Oracle 11.2 is Dec. 2020. Django 1.11 will be
supported until April 2020 which almost reaches this date. Django 2.0
officially supports Oracle 12.1+.

Default MySQL isolation level is read committed
-----------------------------------------------

MySQL's default isolation level, repeatable read, may cause data loss in
typical Django usage. To prevent that and for consistency with other databases,
the default isolation level is now read committed. You can use the
:setting:`DATABASES` setting to :ref:`use a different isolation level
<mysql-isolation-level>`, if needed.

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

A migration for :attr:`django.contrib.auth.models.User.last_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 last names, use a custom
form::

    from django.contrib.auth.forms import UserChangeForm

    class MyUserChangeForm(UserChangeForm):
        last_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)

``QuerySet.reverse()`` and ``last()`` are prohibited after slicing
------------------------------------------------------------------

Calling ``QuerySet.reverse()`` or ``last()`` on a sliced queryset leads to
unexpected results due to the slice being applied after reordering. This is
now prohibited, e.g.::

    >>> Model.objects.all()[:2].reverse()
    Traceback (most recent call last):
    ...
    TypeError: Cannot reverse a query once a slice has been taken.

Form fields no longer accept optional arguments as positional arguments
-----------------------------------------------------------------------

To help prevent runtime errors due to incorrect ordering of form field
arguments, optional arguments of built-in form fields are no longer accepted
as positional arguments. For example::

    forms.IntegerField(25, 10)

raises an exception and should be replaced with::

    forms.IntegerField(max_value=25, min_value=10)

``call_command()`` validates the options it receives
----------------------------------------------------

``call_command()`` now validates that the argument parser of the command being
called defines all of the options passed to ``call_command()``.

For custom management commands that use options not created using
``parser.add_argument()``, add a ``stealth_options`` attribute on the command::

    class MyCommand(BaseCommand):
        stealth_options = ('option_name', ...)

Indexes no longer accept positional arguments
---------------------------------------------

For example::

    models.Index(['headline', '-pub_date'], 'index_name')

raises an exception and should be replaced with::

    models.Index(fields=['headline', '-pub_date'], name='index_name')

Foreign key constraints are now enabled on SQLite
-------------------------------------------------

This will appear as a backwards-incompatible change (``IntegrityError:
FOREIGN KEY constraint failed``) if attempting to save an existing model
instance that's violating a foreign key constraint.

Foreign keys are now created with ``DEFERRABLE INITIALLY DEFERRED`` instead of
``DEFERRABLE IMMEDIATE``. Thus, tables may need to be rebuilt to recreate
foreign keys with the new definition, particularly if you're using a pattern
like this::

    from django.db import transaction

    with transaction.atomic():
        Book.objects.create(author_id=1)
        Author.objects.create(id=1)

If you don't recreate the foreign key as ``DEFERRED``, the first ``create()``
would fail now that foreign key constraints are enforced.

Backup your database first! After upgrading to Django 2.0, you can then
rebuild tables using a script similar to this::

    from django.apps import apps
    from django.db import connection

    for app in apps.get_app_configs():
        for model in app.get_models(include_auto_created=True):
            if model._meta.managed and not (model._meta.proxy or model._meta.swapped):
                for base in model.__bases__:
                    if hasattr(base, '_meta'):
                        base._meta.local_many_to_many = []
                model._meta.local_many_to_many = []
                with connection.schema_editor() as editor:
                    editor._remake_table(model)

This script hasn't received extensive testing and needs adaption for various
cases such as multiple databases. Feel free to contribute improvements.

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

* The ``SessionAuthenticationMiddleware`` class is removed. It provided no
  functionality since session authentication is unconditionally enabled in
  Django 1.10.

* The default HTTP error handlers (``handler404``, etc.) are now callables
  instead of dotted Python path strings. Django favors callable references
  since they provide better performance and debugging experience.

* :class:`~django.views.generic.base.RedirectView` no longer silences
  ``NoReverseMatch`` if the ``pattern_name`` doesn't exist.

* When :setting:`USE_L10N` is off, :class:`~django.forms.FloatField` and
  :class:`~django.forms.DecimalField` now respect :setting:`DECIMAL_SEPARATOR`
  and :setting:`THOUSAND_SEPARATOR` during validation. For example, with the
  settings::

     USE_L10N = False
     USE_THOUSAND_SEPARATOR = True
     DECIMAL_SEPARATOR = ','
     THOUSAND_SEPARATOR = '.'

  an input of ``"1.345"`` is now converted to ``1345`` instead of ``1.345``.

* Subclasses of :class:`~django.contrib.auth.models.AbstractBaseUser` are no
  longer required to implement ``get_short_name()`` and ``get_full_name()``.
  (The base implementations that raise ``NotImplementedError`` are removed.)
  ``django.contrib.admin`` uses these methods if implemented but doesn't
  require them. Third-party apps that use these methods may want to adopt a
  similar approach.

* The ``FIRST_DAY_OF_WEEK`` and ``NUMBER_GROUPING`` format settings are now
  kept as integers in JavaScript and JSON i18n view outputs.

* :meth:`~django.test.TransactionTestCase.assertNumQueries` now ignores
  connection configuration queries. Previously, if a test opened a new database
  connection, those queries could be included as part of the
  ``assertNumQueries()`` count.

* The ``PASSWORD_RESET_TIMEOUT_DAYS`` setting is more properly respected in
  ``contrib.auth`` password reset. Previously, resets were allowed for one day
  longer than expected. For example, with the default of
  ``PASSWORD_RESET_TIMEOUT_DAYS = 3``, password reset tokens are now valid for
  72 hours rather than 96 hours.

* The default size of the Oracle test tablespace is increased from 20M to 50M
  and the default autoextend size is increased from 10M to 25M.

* To improve performance when streaming large result sets from the database,
  :meth:`.QuerySet.iterator` now fetches 2000 rows at a time instead of 100.
  The old behavior can be restored using the ``chunk_size`` parameter. For
  example::

      Book.objects.iterator(chunk_size=100)

* Providing unknown package names in the ``packages`` argument of the
  :class:`~django.views.i18n.JavaScriptCatalog` view now raises ``ValueError``
  instead of passing silently.

* A model instance's primary key now appears in the default ``Model.__str__()``
  method, e.g. ``Question object (1)``.

* ``makemigrations`` now detects changes to the model field ``limit_choices_to``
  option. Add this to your existing migrations or accept an auto-generated
  migration for fields that use it.

* Performing queries that require :ref:`automatic spatial transformations
  <automatic-spatial-transformations>` now raises ``NotImplementedError``
  on MySQL instead of silently using non-transformed geometries.

* ``django.core.exceptions.DjangoRuntimeWarning`` is removed. It was only used
  in the cache backend as an intermediate class in ``CacheKeyWarning``'s
  inheritance of ``RuntimeWarning``.

* Renamed ``BaseExpression._output_field`` to ``output_field``. You may need
  to update custom expressions.

* In older versions, forms and formsets combine their ``Media`` with widget
  ``Media`` by concatenating the two. The combining now tries to :ref:`preserve
  the relative order of elements in each list <form-media-asset-order>`.
  ``MediaOrderConflictWarning`` is issued if the order can't be preserved.

.. _deprecated-features-2.0:

Features deprecated in 2.0
==========================

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

* The ``django.db.backends.postgresql_psycopg2`` module is deprecated in favor
  of ``django.db.backends.postgresql``. It's been an alias since Django 1.9.
  This only affects code that imports from the module directly. The
  ``DATABASES`` setting can still use
  ``'django.db.backends.postgresql_psycopg2'``, though you can simplify that by
  using the ``'django.db.backends.postgresql'`` name added in Django 1.9.

* ``django.shortcuts.render_to_response()`` is deprecated in favor of
  :func:`django.shortcuts.render`. ``render()`` takes the same arguments
  except that is also requires a ``request``.

* The ``DEFAULT_CONTENT_TYPE`` setting is deprecated. It doesn't interact well
  well with third-party apps and is obsolete since HTML5 has mostly superseded
  XHTML.

* ``HttpRequest.xreadlines()`` is deprecated in favor of iterating over the
  request.

.. _removed-features-2.0:

Features removed in 2.0
=======================

These features have reached the end of their deprecation cycle and are removed
in Django 2.0. See :ref:`deprecated-features-1.9` and
:ref:`deprecated-features-1.10` for details, including how to remove usage of
these features.

* The ``weak`` argument to ``django.dispatch.signals.Signal.disconnect()`` is
  removed.

* ``django.db.backends.base.BaseDatabaseOperations.check_aggregate_support()``
  is removed.

* The ``django.forms.extras`` package is removed.

* The ``assignment_tag`` helper is removed.

* The ``host`` argument to ``SimpleTestCase.assertsRedirects()`` is removed.
  The compatibility layer which allows absolute URLs to be considered equal to
  relative ones when the path is identical is also removed.

* ``Field.rel`` and ``Field.remote_field.to`` are removed.

* The ``on_delete`` argument for ``ForeignKey`` and ``OneToOneField`` are now
  required.

* ``django.db.models.fields.add_lazy_relation()`` is removed.

* When time zone support is enabled, database backends that don't support time
  zones no longer convert aware datetimes to naive values in UTC anymore when
  such values are passed as parameters to SQL queries executed outside of the
  ORM, e.g. with ``cursor.execute()``.

* ``django.contrib.auth.tests.utils.skipIfCustomUser()`` is removed.

* The ``GeoManager`` and ``GeoQuerySet`` classes are removed.

* The ``django.contrib.gis.geoip`` module is removed.

* The ``supports_recursion`` check for template loaders is removed from:

  * ``django.template.engine.Engine.find_template()``
  * ``django.template.loader_tags.ExtendsNode.find_template()``
  * ``django.template.loaders.base.Loader.supports_recursion()``
  * ``django.template.loaders.cached.Loader.supports_recursion()``

* The ``load_template`` and ``load_template_sources`` template loader methods
  are removed.

* The ``template_dirs`` argument for template loaders is removed:

  * ``django.template.loaders.base.Loader.get_template()``
  * ``django.template.loaders.cached.Loader.cache_key()``
  * ``django.template.loaders.cached.Loader.get_template()``
  * ``django.template.loaders.cached.Loader.get_template_sources()``
  * ``django.template.loaders.filesystem.Loader.get_template_sources()``

* ``django.template.loaders.base.Loader.__call__()`` is removed.

* Support for custom error views that don't accept an ``exception`` parameter
  is removed.

* The ``mime_type`` attribute of ``django.utils.feedgenerator.Atom1Feed`` and
  ``django.utils.feedgenerator.RssFeed`` is removed.

* The ``app_name`` argument to ``include()`` is removed.

* Support for passing a 3-tuple (including ``admin.site.urls``) as the first
  argument to ``include()`` is removed.

* Support for setting a URL instance namespace without an application namespace
  is removed.

* ``Field._get_val_from_obj()`` is removed.

* ``django.template.loaders.eggs.Loader`` is removed.

* The ``current_app`` parameter to the ``contrib.auth`` function-based views is
  removed.

* The ``callable_obj`` keyword argument to
  ``SimpleTestCase.assertRaisesMessage()`` is removed.

* Support for the ``allow_tags`` attribute on ``ModelAdmin`` methods is
  removed.

* The ``enclosure`` keyword argument to ``SyndicationFeed.add_item()`` is
  removed.

* The ``django.template.loader.LoaderOrigin`` and
  ``django.template.base.StringOrigin`` aliases for
  ``django.template.base.Origin`` are removed.

* The ``makemigrations --exit`` option is removed.

* Support for direct assignment to a reverse foreign key or many-to-many
  relation is removed.

* The ``get_srid()`` and ``set_srid()`` methods of
  ``django.contrib.gis.geos.GEOSGeometry`` are removed.

* The ``get_x()``, ``set_x()``, ``get_y()``, ``set_y()``, ``get_z()``, and
  ``set_z()`` methods of ``django.contrib.gis.geos.Point`` are removed.

* The ``get_coords()`` and ``set_coords()`` methods of
  ``django.contrib.gis.geos.Point`` are removed.

* The ``cascaded_union`` property of ``django.contrib.gis.geos.MultiPolygon``
  is removed.

* ``django.utils.functional.allow_lazy()`` is removed.

* The ``shell --plain`` option is removed.

* The ``django.core.urlresolvers`` module is removed.

* ``CommaSeparatedIntegerField`` is removed, except for support in historical
  migrations.

* The template ``Context.has_key()`` method is removed.

* Support for the ``django.core.files.storage.Storage.accessed_time()``,
  ``created_time()``, and ``modified_time()`` methods is removed.

* Support for query lookups using the model name when
  ``Meta.default_related_name`` is set is removed.

* The MySQL ``__search`` lookup is removed.

* The shim for supporting custom related manager classes without a
  ``_apply_rel_filters()`` method is removed.

* Using ``User.is_authenticated()`` and ``User.is_anonymous()`` as methods
  rather than properties is no longer supported.

* The  ``Model._meta.virtual_fields`` attribute is removed.

* The keyword arguments ``virtual_only`` in ``Field.contribute_to_class()`` and
  ``virtual`` in ``Model._meta.add_field()`` are removed.

* The ``javascript_catalog()`` and ``json_catalog()`` views are removed.

* ``django.contrib.gis.utils.precision_wkt()`` is removed.

* In multi-table inheritance, implicit promotion of a ``OneToOneField`` to a
  ``parent_link`` is removed.

* Support for ``Widget._format_value()`` is removed.

* ``FileField`` methods ``get_directory_name()`` and ``get_filename()`` are
  removed.

* The ``mark_for_escaping()`` function and the classes it uses: ``EscapeData``,
  ``EscapeBytes``, ``EscapeText``, ``EscapeString``, and ``EscapeUnicode`` are
  removed.

* The ``escape`` filter now uses ``django.utils.html.conditional_escape()``.

* ``Manager.use_for_related_fields`` is removed.

* Model ``Manager`` inheritance follows MRO inheritance rules. The requirement
  to use ``Meta.manager_inheritance_from_future`` to opt-in to the behavior is
  removed.

* Support for old-style middleware using ``settings.MIDDLEWARE_CLASSES`` is
  removed.