django/docs/releases/2.2.txt

============================================
Django 2.2 release notes - UNDER DEVELOPMENT
============================================

*Expected April 2019*

Welcome to Django 2.2!

These release notes cover the :ref:`new features <whats-new-2.2>`, as well as
some :ref:`backwards incompatible changes <backwards-incompatible-2.2>` you'll
want to be aware of when upgrading from Django 2.1 or earlier. We've
:ref:`begun the deprecation process for some features
<deprecated-features-2.2>`.

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

Django 2.2 is designated as a :term:`long-term support release`. It will
receive security updates for at least three years after its release. Support
for the previous LTS, Django 1.11, will end in April 2020.

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

Django 2.2 supports Python 3.5, 3.6, and 3.7. We **highly recommend** and only
officially support the latest release of each series.

.. _whats-new-2.2:

What's new in Django 2.2
========================

Constraints
-----------

The new :class:`~django.db.models.CheckConstraint` and
:class:`~django.db.models.UniqueConstraint` classes enable adding custom
database constraints. Constraints are added to models using the
:attr:`Meta.constraints <django.db.models.Options.constraints>` option.

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

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

* Added a CSS class to the column headers of
  :class:`~django.contrib.admin.TabularInline`.

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

* The ``HttpRequest`` is now passed as the first positional argument to
  :meth:`.RemoteUserBackend.configure_user`, if it accepts it.

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

* Added Oracle support for the
  :class:`~django.contrib.gis.db.models.functions.Envelope` function.

* Added SpatiaLite support for the :lookup:`coveredby` and :lookup:`covers`
  lookups.

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

* The new ``ordering`` argument for
  :class:`~django.contrib.postgres.aggregates.ArrayAgg` and
  :class:`~django.contrib.postgres.aggregates.StringAgg` determines the
  ordering of the aggregated elements.

* The new :class:`~django.contrib.postgres.indexes.BTreeIndex`,
  :class:`~django.contrib.postgres.indexes.HashIndex` and
  :class:`~django.contrib.postgres.indexes.SpGistIndex` classes allow
  creating ``B-Tree``, ``hash``, and ``SP-GiST`` indexes in the database.

* :class:`~django.contrib.postgres.indexes.BrinIndex` now has the
  ``autosummarize`` parameter.

* The new ``search_type`` parameter of
  :class:`~django.contrib.postgres.search.SearchQuery` allows searching for
  a phrase or raw expression.

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

* Added path matching to the :option:`collectstatic --ignore` option so that
  patterns like ``/vendor/*.js`` can be used.

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

* Added result streaming for :meth:`.QuerySet.iterator` on SQLite.

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

* The new :meth:`View.setup <django.views.generic.base.View.setup>` hook
  initializes view attributes before calling
  :meth:`~django.views.generic.base.View.dispatch`. It allows mixins to setup
  instance attributes for reuse in child classes.

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

* Added support and translations for the Armenian language.

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

* The new :option:`--force-color` option forces colorization of the command
  output.

* :djadmin:`inspectdb` now creates models for foreign tables on PostgreSQL.

* :option:`inspectdb --include-views` now creates models for materialized views
  on Oracle and PostgreSQL.

* The new :option:`inspectdb --include-partitions` option allows creating
  models for partition tables on PostgreSQL. In older versions, models are
  created child tables instead the parent.

* :djadmin:`inspectdb` now introspects :class:`~django.db.models.DurationField`
  for Oracle and PostgreSQL, and :class:`~django.db.models.AutoField` for
  SQLite.

* On Oracle, :djadmin:`dbshell` is wrapped with ``rlwrap``, if available.
  ``rlwrap`` provides a command history and editing of keyboard input.

* The new :option:`makemigrations --no-header` option avoids writing header
  comments in generated migration file(s). This option is also available for
  :djadmin:`squashmigrations`.

* :djadmin:`runserver` can now use `Watchman
  <https://facebook.github.io/watchman/>`_ to improve the performance of
  watching a large number of files for changes.

Migrations
~~~~~~~~~~

* The new :option:`migrate --plan` option prints the list of migration
  operations that will be performed.

* ``NoneType`` can now be serialized in migrations.

* You can now :ref:`register custom serializers <custom-migration-serializers>`
  for migrations.

Models
~~~~~~

* Added support for PostgreSQL operator classes (:attr:`.Index.opclasses`).

* Added support for partial indexes (:attr:`.Index.condition`).

* Added the :class:`~django.db.models.functions.NullIf` and
  :class:`~django.db.models.functions.Reverse` database functions, as well as
  many :ref:`math database functions <math-functions>`.

* Setting the new ``ignore_conflicts`` parameter of
  :meth:`.QuerySet.bulk_create` to ``True`` tells the database to ignore
  failure to insert rows that fail uniqueness constraints or other checks.

* The new :class:`~django.db.models.functions.ExtractIsoYear` function extracts
  ISO-8601 week-numbering years from :class:`~django.db.models.DateField` and
  :class:`~django.db.models.DateTimeField`, and the new :lookup:`iso_year`
  lookup allows querying by an ISO-8601 week-numbering year.

* The new :meth:`.QuerySet.bulk_update` method allows efficiently updating
  specific fields on multiple model instances.

* Django no longer always starts a transaction when a single query is being
  performed, such as ``Model.save()``, ``QuerySet.update()``, and
  ``Model.delete()``. This improves the performance of autocommit by reducing
  the number of database round trips.

* Added SQLite support for the :class:`~django.db.models.StdDev` and
  :class:`~django.db.models.Variance` functions.

* The handling of ``DISTINCT`` aggregation is added to the
  :class:`~django.db.models.Aggregate` class. Adding :attr:`allow_distinct =
  True <django.db.models.Aggregate.allow_distinct>` as a class attribute on
  ``Aggregate`` subclasses allows a ``distinct`` keyword argument to be
  specified on initialization to ensure that the aggregate function is only
  called for each distinct value of ``expressions``.

* The :meth:`.RelatedManager.add`, :meth:`~.RelatedManager.create`,
  :meth:`~.RelatedManager.remove`,  :meth:`~.RelatedManager.set`,
  ``get_or_create()``, and ``update_or_create()`` methods are now allowed on
  many-to-many relationships with intermediate models. The new
  ``through_defaults`` argument is used to specify values for new intermediate
  model instance(s).

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

* Added :attr:`.HttpRequest.headers` to allow simple access to a request's
  headers.

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

* You can now deserialize data using natural keys containing :ref:`forward
  references <natural-keys-and-forward-references>` by passing
  ``handle_forward_references=True`` to ``serializers.deserialize()``.
  Additionally, :djadmin:`loaddata` handles forward references automatically.

Tests
~~~~~

* The new :meth:`.SimpleTestCase.assertURLEqual` assertion checks for a given
  URL, ignoring the ordering of the query string.
  :meth:`~.SimpleTestCase.assertRedirects` uses the new assertion.

* The test :class:`~.django.test.Client` now supports automatic JSON
  serialization of list and tuple ``data`` when
  ``content_type='application/json'``.

* The new :setting:`ORACLE_MANAGED_FILES <TEST_ORACLE_MANAGED_FILES>` test
  database setting allows using Oracle Managed Files (OMF) tablespaces.

* Deferrable database constraints are now checked at the end of each
  :class:`~django.test.TestCase` test on SQLite 3.20+, just like on other
  backends that support deferrable constraints. These checks aren't implemented
  for older versions of SQLite because they would require expensive table
  introspection there.

* :class:`~django.test.runner.DiscoverRunner` now skips the setup of databases
  not :ref:`referenced by tests<testing-multi-db>`.

URLs
~~~~

* The new :attr:`.ResolverMatch.route` attribute stores the route of the
  matching URL pattern.

Validators
~~~~~~~~~~

* :class:`.MaxValueValidator`, :class:`.MinValueValidator`,
  :class:`.MinLengthValidator`, and :class:`.MaxLengthValidator` now accept
  a callable ``limit_value``.

.. _backwards-incompatible-2.2:

Backwards incompatible changes in 2.2
=====================================

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

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

* Third-party database backends must implement support for table check
  constraints or set ``DatabaseFeatures.supports_table_check_constraints`` to
  ``False``.

* Third party database backends must implement support for ignoring
  constraints or uniqueness errors while inserting or set
  ``DatabaseFeatures.supports_ignore_conflicts`` to ``False``.

* Third party database backends must implement introspection for
  ``DurationField`` or set ``DatabaseFeatures.can_introspect_duration_field``
  to ``False``.

* ``DatabaseFeatures.uses_savepoints`` now defaults to ``True``.

* Third party database backends must implement support for partial indexes or
  set ``DatabaseFeatures.supports_partial_indexes`` to ``False``.

* ``DatabaseIntrospection.table_name_converter()`` and
  ``column_name_converter()`` are removed. Third party database backends may
  need to instead implement ``DatabaseIntrospection.identifier_converter()``.
  In that case, the constraint names that
  ``DatabaseIntrospection.get_constraints()`` returns must be normalized by
  ``identifier_converter()``.

* SQL generation for indexes is moved from :class:`~django.db.models.Index` to
  ``SchemaEditor`` and these ``SchemaEditor`` methods are added:

  * ``_create_primary_key_sql()`` and ``_delete_primary_key_sql()``
  * ``_delete_index_sql()`` (to pair with ``_create_index_sql()``)
  * ``_delete_unique_sql`` (to pair with ``_create_unique_sql()``)
  * ``_delete_fk_sql()`` (to pair with ``_create_fk_sql()``)
  * ``_create_check_sql()`` and ``_delete_check_sql()``

* The third argument of ``DatabaseWrapper.__init__()``,
  ``allow_thread_sharing``, is removed.

Admin actions are no longer collected from base ``ModelAdmin`` classes
----------------------------------------------------------------------

For example, in older versions of Django::

    from django.contrib import admin

    class BaseAdmin(admin.ModelAdmin):
        actions = ['a']

    class SubAdmin(BaseAdmin):
        actions = ['b']

``SubAdmin`` will have actions ``'a'`` and ``'b'``.

Now ``actions`` follows standard Python inheritance. To get the same result as
before::

    class SubAdmin(BaseAdmin):
        actions = BaseAdmin.actions + ['b']

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

* Support for GDAL 1.9 and 1.10 is dropped.

``TransactionTestCase`` serialized data loading
-----------------------------------------------

Initial data migrations are now loaded in
:class:`~django.test.TransactionTestCase` at the end of the test, after the
database flush. In older versions, this data was loaded at the beginning of the
test, but this prevents the :option:`test --keepdb` option from working
properly (the database was empty at the end of the whole test suite). This
change shouldn't have an impact on your tests unless you've customized
:class:`~django.test.TransactionTestCase`'s internals.

``sqlparse`` is required dependency
-----------------------------------

To simplify a few parts of Django's database handling, `sqlparse
<https://pypi.org/project/sqlparse/>`_ is now a required dependency. It's
automatically installed along with Django.

``cached_property`` aliases
---------------------------

In usage like::

    from django.utils.functional import cached_property

    class A:

        @cached_property
        def base(self):
            return ...

        alias = base

``alias`` is not cached. Where the problem can be detected (Python 3.6 and
later), such usage now raises ``TypeError: Cannot assign the same
cached_property to two different names ('base' and 'alias').``

Use this instead::

    import operator

    class A:

        ...

        alias = property(operator.attrgetter('base'))

Permissions for proxy models
----------------------------

:ref:`Permissions for proxy models <proxy-models-permissions-topic>` are now
created using the content type of the proxy model rather than the content type
of the concrete model. A migration will update existing permissions when you
run :djadmin:`migrate`.

In the admin, the change is transparent for proxy models having the same
``app_label`` as their concrete model. However, in older versions, users with
permissions for a proxy model with a *different* ``app_label`` than its
concrete model couldn't access the model in the admin. That's now fixed, but
you might want to audit the permissions assignments for such proxy models
(``[add|view|change|delete]_myproxy``) prior to upgrading to ensure the new
access is appropriate.

Finally, proxy model permission strings must be updated to use their own
``app_label``. For example, for ``app.MyProxyModel`` inheriting from
``other_app.ConcreteModel``, update
``user.has_perm('other_app.add_myproxymodel')`` to
``user.has_perm('app.add_myproxymodel')``.

Merging of form ``Media`` assets
--------------------------------

Form ``Media`` assets are now merged using a topological sort algorithm, as the
old pairwise merging algorithm is insufficient for some cases. CSS and
JavaScript files which don't include their dependencies may now be sorted
incorrectly (where the old algorithm produced results correctly by
coincidence).

Audit all ``Media`` classes for any missing dependencies. For example,
widgets depending on ``django.jQuery`` must specify
``js=['admin/js/jquery.init.js', ...]`` when :ref:`declaring form media assets
<assets-as-a-static-definition>`.

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

* To improve readability, the ``UUIDField`` form field now displays values with
  dashes, e.g. ``550e8400-e29b-41d4-a716-446655440000`` instead of
  ``550e8400e29b41d4a716446655440000``.

* On SQLite, ``PositiveIntegerField`` and ``PositiveSmallIntegerField`` now
  include a check constraint to prevent negative values in the database. If you
  have existing invalid data and run a migration that recreates a table, you'll
  see ``CHECK constraint failed``.

* For consistency with WSGI servers, the test client now sets the
  ``Content-Length`` header to a string rather than an integer.

* The return value of :func:`django.utils.text.slugify` is no longer marked as
  HTML safe.

* The default truncation character used by the :tfilter:`urlizetrunc`,
  :tfilter:`truncatechars`, :tfilter:`truncatechars_html`,
  :tfilter:`truncatewords`, and :tfilter:`truncatewords_html` template filters
  is now the real ellipsis character (``…``) instead of 3 dots. You may have to
  adapt some test output comparisons.

* Support for bytestring paths in the template filesystem loader is removed.

* :func:`django.utils.http.urlsafe_base64_encode` now returns a string instead
  of a bytestring, and :func:`django.utils.http.urlsafe_base64_decode` may no
  longer be passed a bytestring.

* Support for ``cx_Oracle`` < 6.0 is removed.

* The minimum supported version of ``mysqlclient`` is increased from 1.3.7 to
  1.3.13.

* The minimum supported version of SQLite is increased from 3.7.15 to 3.8.3.

* In an attempt to provide more semantic query data, ``NullBooleanSelect`` now
  renders ``<option>`` values of ``unknown``, ``true``, and ``false`` instead
  of ``1``, ``2``, and ``3``. For backwards compatibility, the old values are
  still accepted as data.

* :attr:`Group.name <django.contrib.auth.models.Group.name>` ``max_length``
  is increased from 80 to 150 characters.

* Tests that violate deferrable database constraints now error when run on
  SQLite 3.20+, just like on other backends that support such constraints.

* To catch usage mistakes, the test :class:`~django.test.Client` and
  :func:`django.utils.http.urlencode` now raise ``TypeError`` if ``None`` is
  passed as a value to encode because ``None`` can't be encoded in GET and POST
  data. Either pass an empty string or omit the value.

* The :djadmin:`ping_google` management command now defaults to ``https``
  instead of ``http`` for the sitemap's URL. If your site uses http, use the
  new :option:`ping_google --sitemap-uses-http` option. If you use the
  :func:`~django.contrib.sitemaps.ping_google` function, set the new
  ``sitemap_uses_https`` argument to ``False``.

* :djadmin:`runserver` no longer supports `pyinotify` (replaced by Watchman).

* The :class:`~django.db.models.Avg`, :class:`~django.db.models.StdDev`, and
  :class:`~django.db.models.Variance` aggregate functions now return a
  ``Decimal`` instead of a ``float`` when the input is ``Decimal``.

* Tests will fail on SQLite if apps without migrations have relations to apps
  with migrations. This has been a documented restriction since migrations were
  added in Django 1.7, but it fails more reliably now. You'll see tests failing
  with errors like ``no such table: <app_label>_<model>``. This was observed
  with several third-party apps that had models in tests without migrations.
  You must add migrations for such models.

.. _deprecated-features-2.2:

Features deprecated in 2.2
==========================

Model ``Meta.ordering`` will no longer affect ``GROUP BY`` queries
------------------------------------------------------------------

A model's ``Meta.ordering`` affecting ``GROUP BY`` queries (such as
``.annotate().values()``) is a common source of confusion. Such queries now
issue a deprecation warning with the advice to add an ``order_by()`` to retain
the current query. ``Meta.ordering`` will be ignored in such queries starting
in Django 3.1.

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

* ``django.utils.timezone.FixedOffset`` is deprecated in favor of
  :class:`datetime.timezone`.

* The undocumented ``QuerySetPaginator`` alias of
  ``django.core.paginator.Paginator`` is deprecated.

* The ``FloatRangeField`` model and form fields in ``django.contrib.postgres``
  are deprecated in favor of a new name, ``DecimalRangeField``, to match the
  underlying ``numrange`` data type used in the database.

* The ``FILE_CHARSET`` setting is deprecated. Starting with Django 3.1, files
  read from disk must be UTF-8 encoded.

* ``django.contrib.staticfiles.storage.CachedStaticFilesStorage`` is
  deprecated due to the intractable problems that it has. Use
  :class:`.ManifestStaticFilesStorage` or a third-party cloud storage instead.

* :meth:`.RemoteUserBackend.configure_user` is now passed ``request`` as the
  first positional argument, if it accepts it. Support for overrides that don't
  accept it will be removed in Django 3.1.

* The :attr:`.SimpleTestCase.allow_database_queries`,
  :attr:`.TransactionTestCase.multi_db`, and :attr:`.TestCase.multi_db`
  attributes are deprecated in favor of :attr:`.SimpleTestCase.databases`,
  :attr:`.TransactionTestCase.databases`, and :attr:`.TestCase.databases`.
  These new attributes allow databases dependencies to be declared in order to
  prevent unexpected queries against non-default databases to leak state
  between tests. The previous behavior of ``allow_database_queries=True`` and
  ``multi_db=True`` can be achieved by setting ``databases='__all__'``.