Django 2.2 release notes

April 1, 2019

Welcome to Django 2.2!

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 2.1 or earlier. 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。

Django 2.2 is designated as a 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 兼容性

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.

What’s new in Django 2.2

Constraints

The new CheckConstraint and UniqueConstraint classes enable adding custom database constraints. Constraints are added to models using the Meta.constraints option.

次要特性

django.contrib.admin

• Added a CSS class to the column headers of TabularInline.

django.contrib.auth

• The HttpRequest is now passed as the first positional argument to RemoteUserBackend.configure_user(), if it accepts it.

django.contrib.gis

• Added Oracle support for the Envelope function.
• Added SpatiaLite support for the coveredby and covers lookups.

django.contrib.postgres

• The new ordering argument for ArrayAgg and StringAgg determines the ordering of the aggregated elements.
• The new BTreeIndex, HashIndex and SpGistIndex classes allow creating B-Tree, hash, and SP-GiST indexes in the database.
• BrinIndex now has the autosummarize parameter.
• The new search_type parameter of SearchQuery allows searching for a phrase or raw expression.

django.contrib.staticfiles

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

Database backends

• Added result streaming for QuerySet.iterator() on SQLite.

Generic Views

• The new View.setup hook initializes view attributes before calling dispatch(). It allows mixins to setup instance attributes for reuse in child classes.

国际化

• Added support and translations for the Armenian language.

管理命令

• The new --force-color option forces colorization of the command output.
• inspectdb now creates models for foreign tables on PostgreSQL.
• inspectdb --include-views now creates models for materialized views on Oracle and PostgreSQL.
• The new inspectdb --include-partitions option allows creating models for partition tables on PostgreSQL. In older versions, models are created child tables instead the parent.
• inspectdb now introspects DurationField for Oracle and PostgreSQL, and AutoField for SQLite.
• On Oracle, dbshell is wrapped with rlwrap, if available. rlwrap provides a command history and editing of keyboard input.
• The new makemigrations --no-header option avoids writing header comments in generated migration file(s). This option is also available for squashmigrations.
• runserver can now use Watchman to improve the performance of watching a large number of files for changes.

迁移

• The new migrate --plan option prints the list of migration operations that will be performed.
• NoneType can now be serialized in migrations.
• You can now register custom serializers for migrations.

模型

• Added support for PostgreSQL operator classes (Index.opclasses).
• Added support for partial indexes (Index.condition).
• Added the NullIf and Reverse database functions, as well as many math database functions.
• Setting the new ignore_conflicts parameter of QuerySet.bulk_create() to True tells the database to ignore failure to insert rows that fail uniqueness constraints or other checks.
• The new ExtractIsoYear function extracts ISO-8601 week-numbering years from DateField and DateTimeField, and the new iso_year lookup allows querying by an ISO-8601 week-numbering year.
• The new 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 StdDev and Variance functions.
• The handling of DISTINCT aggregation is added to the Aggregate class. Adding allow_distinct = True 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 RelatedManager.add(), create(), remove(), 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).

请求和响应

• Added HttpRequest.headers to allow simple access to a request’s headers.

序列化

• You can now deserialize data using natural keys containing forward references by passing handle_forward_references=True to serializers.deserialize(). Additionally, loaddata handles forward references automatically.

测试

• The new SimpleTestCase.assertURLEqual() assertion checks for a given URL, ignoring the ordering of the query string. assertRedirects() uses the new assertion.
• The test Client now supports automatic JSON serialization of list and tuple data when content_type='application/json'.
• The new ORACLE_MANAGED_FILES test database setting allows using Oracle Managed Files (OMF) tablespaces.
• Deferrable database constraints are now checked at the end of each 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.
• DiscoverRunner now skips the setup of databases not referenced by tests.

URLs

• The new ResolverMatch.route attribute stores the route of the matching URL pattern.

验证器

• MaxValueValidator, MinValueValidator, MinLengthValidator, and MaxLengthValidator now accept a callable limit_value.

Backwards incompatible changes in 2.2

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。

• 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 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']

django.contrib.gis

• Support for GDAL 1.9 and 1.10 is dropped.

TransactionTestCase serialized data loading

Initial data migrations are now loaded in 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 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 TransactionTestCase‘s internals.

sqlparse is required dependency

To simplify a few parts of Django’s database handling, sqlparse 0.2.2+ 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

Permissions for proxy models 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 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 declaring form media assets.

杂项

• 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 django.utils.text.slugify() is no longer marked as HTML safe.

• The default truncation character used by the urlizetrunc, truncatechars, truncatechars_html, truncatewords, and 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.

• django.utils.http.urlsafe_base64_encode() now returns a string instead of a bytestring, and 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.

• 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 Client and 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 ping_google management command now defaults to https instead of http for the sitemap’s URL. If your site uses http, use the new ping_google --sitemap-uses-http option. If you use the ping_google() function, set the new sitemap_uses_https argument to False.

• runserver no longer supports pyinotify (replaced by Watchman).

• The Avg, StdDev, and 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 cache.delete() or cache.get() now raises ValueError.

• Plural equations for some languages are changed, because the latest versions from Transifex are incorporated.

  注解

  The ability to handle .po files containing different plural equations for the same language was added in Django 2.2.12.

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.

杂项

• django.utils.timezone.FixedOffset is deprecated in favor of 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 ManifestStaticFilesStorage or a third-party cloud storage instead.
• 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 SimpleTestCase.databases, TransactionTestCase.databases, and 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__'.