Django 3.0 release notes

December 2, 2019

Welcome to Django 3.0!

These release notes cover the new features, as well as some backwards incompatible changes you’ll want to be aware of when upgrading from Django 2.2 or earlier. We’ve dropped some features that have reached the end of their deprecation cycle, and we’ve begun the deprecation process for some features.

如果你要更新现有的项目，请看 升级 Django 到最新的版本 指南。

Python 兼容性

Django 3.0 supports Python 3.6, 3.7, 3.8, and 3.9 (as of 3.0.11). We highly recommend and only officially support the latest release of each series.

The Django 2.2.x series is the last to support Python 3.5.

Third-party library support for older version of Django

Following the release of Django 3.0, we suggest that third-party app authors drop support for all versions of Django prior to 2.2. At that time, you should be able to run your package’s tests using python -Wd so that deprecation warnings appear. After making the deprecation warning fixes, your app should be compatible with Django 3.0.

What’s new in Django 3.0

MariaDB support

Django now officially supports MariaDB 10.1 and higher. See MariaDB notes for more details.

ASGI support

Django 3.0 begins our journey to making Django fully async-capable by providing support for running as an ASGI application.

This is in addition to our existing WSGI support. Django intends to support both for the foreseeable future. Async features will only be available to applications that run under ASGI, however.

At this stage async support only applies to the outer ASGI application. Internally everything remains synchronous. Asynchronous middleware, views, etc. are not yet supported. You can, however, use ASGI middleware around Django’s application, allowing you to combine Django with other ASGI frameworks.

There is no need to switch your applications over unless you want to start experimenting with asynchronous code, but we have documentation on deploying with ASGI if you want to learn more.

Note that as a side-effect of this change, Django is now aware of asynchronous event loops and will block you calling code marked as “async unsafe” - such as ORM operations - from an asynchronous context. If you were using Django from async code before, this may trigger if you were doing it incorrectly. If you see a SynchronousOnlyOperation error, then closely examine your code and move any database operations to be in a synchronous child thread.

Exclusion constraints on PostgreSQL

The new ExclusionConstraint class enable adding exclusion constraints on PostgreSQL. Constraints are added to models using the Meta.constraints option.

Filter expressions

Expressions that output BooleanField may now be used directly in QuerySet filters, without having to first annotate and then filter against the annotation.

Enumerations for model field choices

Custom enumeration types TextChoices, IntegerChoices, and Choices are now available as a way to define Field.choices. TextChoices and IntegerChoices types are provided for text and integer fields. The Choices class allows defining a compatible enumeration for other concrete data types. These custom enumeration types support human-readable labels that can be translated and accessed via a property on the enumeration or its members. See Enumeration types for more details and examples.

次要特性

django.contrib.admin

  • Added support for the admin_order_field attribute on properties in ModelAdmin.list_display.
  • The new ModelAdmin.get_inlines() method allows specifying the inlines based on the request or model instance.
  • Select2 library is upgraded from version 4.0.3 to 4.0.7.
  • jQuery is upgraded from version 3.3.1 to 3.4.1.

django.contrib.auth

  • The new reset_url_token attribute in PasswordResetConfirmView allows specifying a token parameter displayed as a component of password reset URLs.
  • Added BaseBackend class to ease customization of authentication backends.
  • Added get_user_permissions() method to mirror the existing get_group_permissions() method.
  • Added HTML autocomplete attribute to widgets of username, email, and password fields in django.contrib.auth.forms for better interaction with browser password managers.
  • createsuperuser now falls back to environment variables for password and required fields, when a corresponding command line argument isn’t provided in non-interactive mode.
  • REQUIRED_FIELDS now supports ManyToManyFields.
  • The new UserManager.with_perm() method returns users that have the specified permission.
  • The default iteration count for the PBKDF2 password hasher is increased from 150,000 to 180,000.

django.contrib.gis

django.contrib.postgres

django.contrib.sessions

django.contrib.syndication

缓存

文件存储

  • The new Storage.get_alternative_name() method allows customizing the algorithm for generating filenames if a file with the uploaded name already exists.

表单

国际化

日志

  • The new reporter_class parameter of AdminEmailHandler allows providing an django.views.debug.ExceptionReporter subclass to customize the traceback text sent to site ADMINS when DEBUG is False.

管理命令

模型

  • Added hash database functions MD5, SHA1, SHA224, SHA256, SHA384, and SHA512.

  • Added the Sign database function.

  • The new is_dst parameter of the Trunc database functions determines the treatment of nonexistent and ambiguous datetimes.

  • connection.queries now shows COPY … TO statements on PostgreSQL.

  • FilePathField now accepts a callable for path.

  • Allowed symmetrical intermediate table for self-referential ManyToManyField.

  • The name attributes of CheckConstraint, UniqueConstraint, and Index now support app label and class interpolation using the '%(app_label)s' and '%(class)s' placeholders.

  • The new Field.descriptor_class attribute allows model fields to customize the get and set behavior by overriding their descriptors.

  • Avg and Sum now support the distinct argument.

  • Added SmallAutoField which acts much like an AutoField except that it only allows values under a certain (database-dependent) limit. Values from 1 to 32767 are safe in all databases supported by Django.

  • AutoField, BigAutoField, and SmallAutoField now inherit from IntegerField, BigIntegerField and SmallIntegerField respectively. System checks and validators are now also properly inherited.

  • FileField.upload_to now supports pathlib.Path.

  • CheckConstraint is now supported on MySQL 8.0.16+.

  • The new allows_group_by_selected_pks_on_model() method of django.db.backends.base.BaseDatabaseFeatures allows optimization of GROUP BY clauses to require only the selected models’ primary keys. By default, it’s supported only for managed models on PostgreSQL.

    To enable the GROUP BY primary key-only optimization for unmanaged models, you have to subclass the PostgreSQL database engine, overriding the features class allows_group_by_selected_pks_on_model() method as you require. See Subclassing the built-in database backends for an example.

请求和响应

安全

测试

  • The new test Client argument raise_request_exception allows controlling whether or not exceptions raised during the request should also be raised in the test. The value defaults to True for backwards compatibility. If it is False and an exception occurs, the test client will return a 500 response with the attribute exc_info, a tuple providing information of the exception that occurred.
  • Tests and test cases to run can be selected by test name pattern using the new test -k option.
  • HTML comparison, as used by assertHTMLEqual(), now treats text, character references, and entity references that refer to the same character as equivalent.
  • Django test runner now supports headless mode for selenium tests on supported browsers. Add the --headless option to enable this mode.
  • Django test runner now supports --start-at and --start-after options to run tests starting from a specific top-level module.
  • Django test runner now supports a --pdb option to spawn a debugger at each error or failure.

Backwards incompatible changes in 3.0

Model.save() when providing a default for the primary key

Model.save() no longer attempts to find a row when saving a new Model instance and a default value for the primary key is provided, and always performs a single INSERT query. In older Django versions, Model.save() performed either an INSERT or an UPDATE based on whether or not the row exists.

This makes calling Model.save() while providing a default primary key value equivalent to passing force_insert=True to model’s save(). Attempts to use a new Model instance to update an existing row will result in an IntegrityError.

In order to update an existing model for a specific primary key value, use the update_or_create() method or QuerySet.filter(pk=…).update(…) instead. For example:

  1. >>> MyModel.objects.update_or_create(pk=existing_pk, defaults={'name': 'new name'})
  2. >>> MyModel.objects.filter(pk=existing_pk).update(name='new name')

数据库后端 API

本节介绍了第三方数据库后端可能需要的更改。

  • The second argument of DatabaseIntrospection.get_geometry_type() is now the row description instead of the column name.
  • DatabaseIntrospection.get_field_type() may no longer return tuples.
  • If the database can create foreign keys in the same SQL statement that adds a field, add SchemaEditor.sql_create_column_inline_fk with the appropriate SQL; otherwise, set DatabaseFeatures.can_create_inline_fk = False.
  • DatabaseFeatures.can_return_id_from_insert and can_return_ids_from_bulk_insert are renamed to can_return_columns_from_insert and can_return_rows_from_bulk_insert.
  • Database functions now handle datetime.timezone formats when created using datetime.timedelta instances (e.g. timezone(timedelta(hours=5)), which would output 'UTC+05:00'). Third-party backends should handle this format when preparing DateTimeField in datetime_cast_date_sql(), datetime_extract_sql(), etc.
  • Entries for AutoField, BigAutoField, and SmallAutoField are added to DatabaseOperations.integer_field_ranges to support the integer range validators on these field types. Third-party backends may need to customize the default entries.
  • DatabaseOperations.fetch_returned_insert_id() is replaced by fetch_returned_insert_columns() which returns a list of values returned by the INSERT … RETURNING statement, instead of a single value.
  • DatabaseOperations.return_insert_id() is replaced by return_insert_columns() that accepts a fields argument, which is an iterable of fields to be returned after insert. Usually this is only the auto-generated primary key.

django.contrib.admin

  • Admin’s model history change messages now prefers more readable field labels instead of field names.

django.contrib.gis

  • Support for PostGIS 2.1 is removed.
  • Support for SpatiaLite 4.1 and 4.2 is removed.
  • Support for GDAL 1.11 and GEOS 3.4 is removed.

Dropped support for PostgreSQL 9.4

Upstream support for PostgreSQL 9.4 ends in December 2019. Django 3.0 supports PostgreSQL 9.5 and higher.

Dropped support for Oracle 12.1

Upstream support for Oracle 12.1 ends in July 2021. Django 2.2 will be supported until April 2022. Django 3.0 officially supports Oracle 12.2 and 18c.

Removed private Python 2 compatibility APIs

While Python 2 support was removed in Django 2.0, some private APIs weren’t removed from Django so that third party apps could continue using them until the Python 2 end-of-life.

Since we expect apps to drop Python 2 compatibility when adding support for Django 3.0, we’re removing these APIs at this time.

  • django.test.utils.str_prefix() - Strings don’t have ‘u’ prefixes in Python 3.
  • django.test.utils.patch_logger() - Use unittest.TestCase.assertLogs() instead.
  • django.utils.lru_cache.lru_cache() - Alias of functools.lru_cache().
  • django.utils.decorators.available_attrs() - This function returns functools.WRAPPER_ASSIGNMENTS.
  • django.utils.decorators.ContextDecorator - Alias of contextlib.ContextDecorator.
  • django.utils._os.abspathu() - Alias of os.path.abspath().
  • django.utils._os.upath() and npath() - These functions do nothing on Python 3.
  • django.utils.six - Remove usage of this vendored library or switch to six.
  • django.utils.encoding.python_2_unicode_compatible() - Alias of six.python_2_unicode_compatible().
  • django.utils.functional.curry() - Use functools.partial() or functools.partialmethod. See 5b1c389603a353625ae1603.
  • django.utils.safestring.SafeBytes - Unused since Django 2.0.

New default value for the FILE_UPLOAD_PERMISSIONS setting

In older versions, the FILE_UPLOAD_PERMISSIONS setting defaults to None. With the default FILE_UPLOAD_HANDLERS, this results in uploaded files having different permissions depending on their size and which upload handler is used.

FILE_UPLOAD_PERMISSIONS now defaults to 0o644 to avoid this inconsistency.

New default values for security settings

To make Django projects more secure by default, some security settings now have more secure default values:

See the What’s New Security section above for more details on these changes.

杂项

  • ContentType.__str__() now includes the model’s app_label to disambiguate models with the same name in different apps.
  • Because accessing the language in the session rather than in the cookie is deprecated, LocaleMiddleware no longer looks for the user’s language in the session and django.contrib.auth.logout() no longer preserves the session’s language after logout.
  • django.utils.html.escape() now uses html.escape() to escape HTML. This converts ' to ' instead of the previous equivalent decimal code '.
  • The django-admin test -k option now works as the unittest -k option rather than as a shortcut for --keepdb.
  • Support for pywatchman < 1.2.0 is removed.
  • urlencode() now encodes iterable values as they are when doseq=False, rather than iterating them, bringing it into line with the standard library urllib.parse.urlencode() function.
  • intword template filter now translates 1.0 as a singular phrase and all other numeric values as plural. This may be incorrect for some languages.
  • Assigning a value to a model’s ForeignKey or OneToOneField '_id' attribute now unsets the corresponding field. Accessing the field afterwards will result in a query.
  • patch_vary_headers() now handles an asterisk '*' according to RFC 7231#section-7.1.4, i.e. if a list of header field names contains an asterisk, then the Vary header will consist of a single asterisk '*'.
  • On MySQL 8.0.16+, PositiveIntegerField and PositiveSmallIntegerField now include a check constraint to prevent negative values in the database.
  • alias=None is added to the signature of Expression.get_group_by_cols().
  • RegexPattern, used by re_path(), no longer returns keyword arguments with None values to be passed to the view for the optional named groups that are missing.

Features deprecated in 3.0

django.utils.encoding.force_text() and smart_text()

The smart_text() and force_text() aliases (since Django 2.0) of smart_str() and force_str() are deprecated. Ignore this deprecation if your code supports Python 2 as the behavior of smart_str() and force_str() is different there.

杂项

  • django.utils.http.urlquote(), urlquote_plus(), urlunquote(), and urlunquote_plus() are deprecated in favor of the functions that they’re aliases for: urllib.parse.quote(), quote_plus(), unquote(), and unquote_plus().
  • django.utils.translation.ugettext(), ugettext_lazy(), ugettext_noop(), ungettext(), and ungettext_lazy() are deprecated in favor of the functions that they’re aliases for: django.utils.translation.gettext(), gettext_lazy(), gettext_noop(), ngettext(), and ngettext_lazy().
  • To limit creation of sessions and hence favor some caching strategies, django.views.i18n.set_language() will stop setting the user’s language in the session in Django 4.0. Since Django 2.1, the language is always stored in the LANGUAGE_COOKIE_NAME cookie.
  • django.utils.text.unescape_entities() is deprecated in favor of html.unescape(). Note that unlike unescape_entities(), html.unescape() evaluates lazy strings immediately.
  • To avoid possible confusion as to effective scope, the private internal utility is_safe_url() is renamed to url_has_allowed_host_and_scheme(). That a URL has an allowed host and scheme doesn’t in general imply that it’s “safe”. It may still be quoted incorrectly, for example. Ensure to also use iri_to_uri() on the path component of untrusted URLs.

Features removed in 3.0

These features have reached the end of their deprecation cycle and are removed in Django 3.0.

See Features deprecated in 2.0 for details on these changes, including how to remove usage of these features.

  • The django.db.backends.postgresql_psycopg2 module is removed.
  • django.shortcuts.render_to_response() is removed.
  • The DEFAULT_CONTENT_TYPE setting is removed.
  • HttpRequest.xreadlines() is removed.
  • Support for the context argument of Field.from_db_value() and Expression.convert_value() is removed.
  • The field_name keyword argument of QuerySet.earliest() and latest() is removed.

See Features deprecated in 2.1 for details on these changes, including how to remove usage of these features.

  • The ForceRHR GIS function is removed.
  • django.utils.http.cookie_date() is removed.
  • The staticfiles and admin_static template tag libraries are removed.
  • django.contrib.staticfiles.templatetags.staticfiles.static() is removed.