Viewing github.com/django/django-stable-4.1.x/docs/releases/2.2.txt

```
========================
```
```
Django 2.2 release notes
```
```
========================
```
```
*April 1, 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

<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, 3.7, 3.8 (as of 2.2.8), and 3.9 (as of

2.2.17). 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 set up

  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`` would 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 0.2.2+

<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.

* Providing an integer in the ``key`` argument of the :meth:`.cache.delete` or

  :meth:`.cache.get` now raises :exc:`ValueError`.

* Plural equations for some languages are changed, because the latest versions

```
  from Transifex are incorporated.
```
```
  .. note::
```

    The ability to handle ``.po`` files containing different plural equations

    for the same language was added in Django 2.2.12.

```
.. _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 ``SimpleTestCase.allow_database_queries``,

  ``TransactionTestCase.multi_db``, and ``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__'``.