---
title: "Django 2.0 版本发行说明"
version: 4.1
locale: zh-hans
source: https://docs.djangoproject.com/zh-hans/4.1/releases/2.0/
canonical: https://djangodocs.dev/zh-hans/4.1/releases/2.0/
---
# Django 2.0 版本发行说明

*2017 年 12 月 2 日*

欢迎来到 Django 2.0 版本!

These release notes cover the [new features](#whats-new-2-0), as well as
some [backwards incompatible changes](#backwards-incompatible-2-0) you'll
want to be aware of when upgrading from Django 1.11 or earlier. We've
[dropped some features](#removed-features-2-0) that have reached the end of
their deprecation cycle, and we've [begun the deprecation process for some
features](#deprecated-features-2-0).

This release starts Django's use of a [loose form of semantic versioning](/zh-hans/4.1/internals/release-process/#internal-release-cadence), but there aren't any major backwards incompatible
changes that might be expected of a 2.0 release. Upgrading should be a similar
amount of effort as past feature releases.

如果你要更新现有的项目，请看 [How to upgrade Django to a newer version](/zh-hans/4.1/howto/upgrade-version/) 指南。

## Python 兼容性

Django 2.0 supports Python 3.4, 3.5, 3.6, and 3.7. We **highly recommend** and
only officially support the latest release of each series.

Django 1.11.x 系列是支持 Python 2.7 版本的最后一个系列。

Django 2.0 will be the last release series to support Python 3.4. If you plan
a deployment of Python 3.4 beyond the end-of-life for Django 2.0 (April 2019),
stick with Django 1.11 LTS (supported until April 2020) instead. Note, however,
that the end-of-life for Python 3.4 is March 2019.

## 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 to 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.

## Django 2.0 新特性

### 简化 URL 路由语法

新版本 [`django.urls.path()`](/zh-hans/4.1/ref/urls/#django.urls.path) 函数使用更简单易读的 URL 路由语法。一个来自 Django 旧版本的例子：

```
url(r'^articles/(?P<year>[0-9]{4})/$', views.year_archive),
```

could be written as:

```
path('articles/<int:year>/', views.year_archive),
```

新版本语法支持对 URL 参数的强制类型转换。在这个例子中，视图将会以数字类型接收参数 `year` 而不是以字符串类型。而且 URLs 的匹配限制也减少了。例如，因为参数 year 并没有像正则表达式中那样明确限制为四位数，year 为 10000 也会匹配成功。

旧版本中的 `django.conf.urls.url()` 函数现在可以在 [`django.urls.re_path()`](/zh-hans/4.1/ref/urls/#django.urls.re_path) 中获取。前者依然保留，向后兼容，并没有立即弃用。旧版本中的 `django.conf.urls.include()` 函数现在可以从 `django.urls` 中导入，这样你就可以在 URLconfs 中使用 `from django.urls import include, path, re_path` 。

重新编写的文档 [URL调度器](/zh-hans/4.1/topics/http/urls/) 涵盖了新的语法并且提供了更多的细节。

### `contrib.admin` 针对移动设备的优化改进

新版本的 admin 可以响应和支持所有主流移动设备。较旧的浏览器可能会遇到不同程度的功能降低。

### Window 表达式

The new [`Window`](/zh-hans/4.1/ref/models/expressions/#django.db.models.expressions.Window) expression allows
adding an `OVER` clause to querysets. You can use [window functions](/zh-hans/4.1/ref/models/database-functions/#window-functions) and [aggregate functions](/zh-hans/4.1/ref/models/querysets/#aggregation-functions) in
the expression.

### 次要特性

#### [`django.contrib.admin`](/zh-hans/4.1/ref/contrib/admin/#module-django.contrib.admin)

- The new [`ModelAdmin.autocomplete_fields`](/zh-hans/4.1/ref/contrib/admin/#django.contrib.admin.ModelAdmin.autocomplete_fields) attribute and
  [`ModelAdmin.get_autocomplete_fields()`](/zh-hans/4.1/ref/contrib/admin/#django.contrib.admin.ModelAdmin.get_autocomplete_fields) method allow using a
  [Select2](https://select2.org/) search widget for `ForeignKey` and
  `ManyToManyField`.

#### [`django.contrib.auth`](/zh-hans/4.1/topics/auth/#module-django.contrib.auth)

- PBKDF2 密码散列器的默认迭代计数从 36,000 增加到 100,000。

#### [`django.contrib.gis`](/zh-hans/4.1/ref/contrib/gis/#module-django.contrib.gis)

- 增加了 [`AsGeoJSON`](/zh-hans/4.1/ref/contrib/gis/functions/#django.contrib.gis.db.models.functions.AsGeoJSON) 函数、 [`GeoHash`](/zh-hans/4.1/ref/contrib/gis/functions/#django.contrib.gis.db.models.functions.GeoHash) 函数、[`IsValid`](/zh-hans/4.1/ref/contrib/gis/functions/#django.contrib.gis.db.models.functions.IsValid) 函数、[`isvalid`](/zh-hans/4.1/ref/contrib/gis/geoquerysets/#std-fieldlookup-isvalid) 查找、以及 [distance lookups](/zh-hans/4.1/ref/contrib/gis/geoquerysets/#distance-lookups) 对 MySQL 的支持。
- 添加了 PostGIS 和 SpatiaLite 支持的两个函数 [`Azimuth`](/zh-hans/4.1/ref/contrib/gis/functions/#django.contrib.gis.db.models.functions.Azimuth) 和 [`LineLocatePoint`](/zh-hans/4.1/ref/contrib/gis/functions/#django.contrib.gis.db.models.functions.LineLocatePoint)。
- 现在所有从 GeoJSON 导入的 [`GEOSGeometry`](/zh-hans/4.1/ref/contrib/gis/geos/#django.contrib.gis.geos.GEOSGeometry) 都设置了其 SRID。
- 添加了 [`OSMWidget.default_zoom`](/zh-hans/4.1/ref/contrib/gis/forms-api/#django.contrib.gis.forms.widgets.OSMWidget.default_zoom) 属性来自定义地图的默认缩放级别。
- Made metadata readable and editable on rasters through the
  [`metadata`](/zh-hans/4.1/ref/contrib/gis/gdal/#django.contrib.gis.gdal.GDALRaster.metadata),
  [`info`](/zh-hans/4.1/ref/contrib/gis/gdal/#django.contrib.gis.gdal.GDALRaster.info), and
  [`metadata`](/zh-hans/4.1/ref/contrib/gis/gdal/#django.contrib.gis.gdal.GDALBand.metadata) attributes.
- 允许使用 `papsz_options` 将 driver-specific creation options 传递给 [`GDALRaster`](/zh-hans/4.1/ref/contrib/gis/gdal/#django.contrib.gis.gdal.GDALRaster) 对象。
- Allowed creating [`GDALRaster`](/zh-hans/4.1/ref/contrib/gis/gdal/#django.contrib.gis.gdal.GDALRaster) objects in
  GDAL's internal virtual filesystem. Rasters can now be [created from and
  converted to binary data](/zh-hans/4.1/ref/contrib/gis/gdal/#gdal-raster-vsimem) in-memory.
- The new [`GDALBand.color_interp()`](/zh-hans/4.1/ref/contrib/gis/gdal/#django.contrib.gis.gdal.GDALBand.color_interp) method returns the color
  interpretation for the band.

#### [`django.contrib.postgres`](/zh-hans/4.1/ref/contrib/postgres/#module-django.contrib.postgres)

- The new `distinct` argument for
  [`ArrayAgg`](/zh-hans/4.1/ref/contrib/postgres/aggregates/#django.contrib.postgres.aggregates.ArrayAgg) determines if
  concatenated values will be distinct.
- The new [`RandomUUID`](/zh-hans/4.1/ref/contrib/postgres/functions/#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
  [`CryptoExtension`](/zh-hans/4.1/ref/contrib/postgres/operations/#django.contrib.postgres.operations.CryptoExtension) migration
  operation.
- [`django.contrib.postgres.indexes.GinIndex`](/zh-hans/4.1/ref/contrib/postgres/indexes/#django.contrib.postgres.indexes.GinIndex) now supports the
  `fastupdate` and `gin_pending_list_limit` parameters.
- The new [`GistIndex`](/zh-hans/4.1/ref/contrib/postgres/indexes/#django.contrib.postgres.indexes.GistIndex) class allows
  creating `GiST` indexes in the database. The new
  [`BtreeGistExtension`](/zh-hans/4.1/ref/contrib/postgres/operations/#django.contrib.postgres.operations.BtreeGistExtension) migration
  operation installs the `btree_gist` extension to add support for operator
  classes that aren't built-in.
- [`inspectdb`](/zh-hans/4.1/ref/django-admin/#django-admin-inspectdb) can now introspect `JSONField` and various
  `RangeField`s (`django.contrib.postgres` must be in `INSTALLED_APPS`).

#### [`django.contrib.sitemaps`](/zh-hans/4.1/ref/contrib/sitemaps/#module-django.contrib.sitemaps)

- Added the `protocol` keyword argument to the
  [`GenericSitemap`](/zh-hans/4.1/ref/contrib/sitemaps/#django.contrib.sitemaps.GenericSitemap) constructor.

#### 缓存

- `cache.set_many()` now returns a list of keys that failed to be inserted.
  For the built-in backends, failed inserts can only happen on memcached.

#### 文件存储

- [`File.open()`](/zh-hans/4.1/ref/files/file/#django.core.files.File.open) can be used as a context
  manager, e.g. `with file.open() as f:`.

#### 表单

- The new `date_attrs` and `time_attrs` arguments for
  [`SplitDateTimeWidget`](/zh-hans/4.1/ref/forms/widgets/#django.forms.SplitDateTimeWidget) and
  [`SplitHiddenDateTimeWidget`](/zh-hans/4.1/ref/forms/widgets/#django.forms.SplitHiddenDateTimeWidget) allow specifying different
  HTML attributes for the `DateInput` and `TimeInput` (or hidden)
  subwidgets.
- The new [`Form.errors.get_json_data()`](/zh-hans/4.1/ref/forms/api/#django.forms.Form.errors.get_json_data) method returns form errors as
  a dictionary suitable for including in a JSON response.

#### 通用视图

- 新属性 [`ContextMixin.extra_context`](/zh-hans/4.1/ref/class-based-views/mixins-simple/#django.views.generic.base.ContextMixin.extra_context) 允许在 `View.as_view()` 添加上下文。

#### 管理命令

- [`inspectdb`](/zh-hans/4.1/ref/django-admin/#django-admin-inspectdb) now translates MySQL's unsigned integer columns to
  `PositiveIntegerField` or `PositiveSmallIntegerField`.
- The new [`makemessages --add-location`](/zh-hans/4.1/ref/django-admin/#cmdoption-makemessages-add-location) option controls the comment
  format in `.po` files.
- [`loaddata`](/zh-hans/4.1/ref/django-admin/#django-admin-loaddata) can now [read from stdin](/zh-hans/4.1/ref/django-admin/#loading-fixtures-stdin).
- The new [`diffsettings --output`](/zh-hans/4.1/ref/django-admin/#cmdoption-diffsettings-output) option allows formatting the output
  in a unified diff format.
- On Oracle, [`inspectdb`](/zh-hans/4.1/ref/django-admin/#django-admin-inspectdb) can now introspect `AutoField` if the
  column is created as an identity column.
- On MySQL, [`dbshell`](/zh-hans/4.1/ref/django-admin/#django-admin-dbshell) now supports client-side TLS certificates.

#### 迁移

- The new [`squashmigrations --squashed-name`](/zh-hans/4.1/ref/django-admin/#cmdoption-squashmigrations-squashed-name) option allows naming the
  squashed migration.

#### 模型

- The new [`StrIndex`](/zh-hans/4.1/ref/models/database-functions/#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](https://docs.oracle.com/en/database/oracle/oracle-database/21/drdaa/intro-to-tools-and-products-supporting-migraiton.html#GUID-14E4817B-F3BC-4D99-B471-A0ACDC303CC9).
- The new `chunk_size` parameter of [`QuerySet.iterator()`](/zh-hans/4.1/ref/models/querysets/#django.db.models.query.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.
- [`QuerySet.earliest()`](/zh-hans/4.1/ref/models/querysets/#django.db.models.query.QuerySet.earliest), [`QuerySet.latest()`](/zh-hans/4.1/ref/models/querysets/#django.db.models.query.QuerySet.latest), and
  [`Meta.get_latest_by`](/zh-hans/4.1/ref/models/options/#django.db.models.Options.get_latest_by) now
  allow ordering by several fields.
- Added the [`ExtractQuarter`](/zh-hans/4.1/ref/models/database-functions/#django.db.models.functions.ExtractQuarter) function to
  extract the quarter from [`DateField`](/zh-hans/4.1/ref/models/fields/#django.db.models.DateField) and
  [`DateTimeField`](/zh-hans/4.1/ref/models/fields/#django.db.models.DateTimeField), and exposed it through the
  [`quarter`](/zh-hans/4.1/ref/models/querysets/#std-fieldlookup-quarter) lookup.
- Added the [`TruncQuarter`](/zh-hans/4.1/ref/models/database-functions/#django.db.models.functions.TruncQuarter) function to
  truncate [`DateField`](/zh-hans/4.1/ref/models/fields/#django.db.models.DateField) and
  [`DateTimeField`](/zh-hans/4.1/ref/models/fields/#django.db.models.DateTimeField) to the first day of a quarter.
- Added the [`db_tablespace`](/zh-hans/4.1/ref/models/indexes/#django.db.models.Index.db_tablespace) parameter to
  class-based indexes.
- If the database supports a native duration field (Oracle and PostgreSQL),
  [`Extract`](/zh-hans/4.1/ref/models/database-functions/#django.db.models.functions.Extract) now works with
  [`DurationField`](/zh-hans/4.1/ref/models/fields/#django.db.models.DurationField).
- Added the `of` argument to [`QuerySet.select_for_update()`](/zh-hans/4.1/ref/models/querysets/#django.db.models.query.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
  [`select_for_update()`](/zh-hans/4.1/ref/models/querysets/#django.db.models.query.QuerySet.select_for_update) is used in conjunction with
  [`select_related()`](/zh-hans/4.1/ref/models/querysets/#django.db.models.query.QuerySet.select_related).
- The new `field_name` parameter of [`QuerySet.in_bulk()`](/zh-hans/4.1/ref/models/querysets/#django.db.models.query.QuerySet.in_bulk) allows fetching
  results based on any unique model field.
- [`CursorWrapper.callproc()`](/zh-hans/4.1/topics/db/sql/#django.db.models.CursorWrapper.callproc) now takes an optional dictionary of keyword
  parameters, if the backend supports this feature. Of Django's built-in
  backends, only Oracle supports it.
- The new [`connection.execute_wrapper()`](/zh-hans/4.1/topics/db/instrumentation/#django.db.backends.base.DatabaseWrapper.execute_wrapper) method allows
  [installing wrappers around execution of database queries](/zh-hans/4.1/topics/db/instrumentation/).
- The new `filter` argument for built-in aggregates allows [adding
  different conditionals](/zh-hans/4.1/ref/models/conditional-expressions/#conditional-aggregation) to multiple aggregations
  over the same fields or relations.
- Added support for expressions in [`Meta.ordering`](/zh-hans/4.1/ref/models/options/#django.db.models.Options.ordering).
- The new `named` parameter of [`QuerySet.values_list()`](/zh-hans/4.1/ref/models/querysets/#django.db.models.query.QuerySet.values_list) allows fetching
  results as named tuples.
- The new [`FilteredRelation`](/zh-hans/4.1/ref/models/querysets/#django.db.models.FilteredRelation) class allows adding an `ON` clause to
  querysets.

#### 分页

- Added [`Paginator.get_page()`](/zh-hans/4.1/ref/paginator/#django.core.paginator.Paginator.get_page)
  to provide the documented pattern of handling invalid page numbers.

#### 请求和响应

- The [`runserver`](/zh-hans/4.1/ref/django-admin/#django-admin-runserver) web server supports HTTP 1.1.

#### 模板

- To increase the usefulness of [`Engine.get_default()`](/zh-hans/4.1/ref/templates/api/#django.template.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.

#### 测试

- Added threading support to [`LiveServerTestCase`](/zh-hans/4.1/topics/testing/tools/#django.test.LiveServerTestCase).
- Added settings that allow customizing the test tablespace parameters for
  Oracle: [`DATAFILE_SIZE`](/zh-hans/4.1/ref/settings/#std-setting-DATAFILE_SIZE), [`DATAFILE_TMP_SIZE`](/zh-hans/4.1/ref/settings/#std-setting-DATAFILE_TMP_SIZE),
  [`DATAFILE_EXTSIZE`](/zh-hans/4.1/ref/settings/#std-setting-DATAFILE_EXTSIZE), and [`DATAFILE_TMP_EXTSIZE`](/zh-hans/4.1/ref/settings/#std-setting-DATAFILE_TMP_EXTSIZE).

#### 验证器

- The new [`ProhibitNullCharactersValidator`](/zh-hans/4.1/ref/validators/#django.core.validators.ProhibitNullCharactersValidator) disallows the null
  character in the input of the [`CharField`](/zh-hans/4.1/ref/forms/fields/#django.forms.CharField) form field
  and its subclasses. Null character input was observed from vulnerability
  scanning tools. Most databases silently discard null characters, but
  psycopg2 2.7+ raises an exception when trying to save a null character to
  a char/text field with PostgreSQL.

## 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. Python's [`-b`](https://docs.python.org/3/using/cmdline.html#cmdoption-b) option may help detect
that mistake in your code.

For example, `reverse()` now uses `str()` instead of `force_text()` to
coerce the `args` and `kwargs` it receives, prior to their placement in
the URL. For bytestrings, this creates a string with an undesired `b` prefix
as well as additional quotes (`str(b'foo')` is `"b'foo'"`). To adapt, call
`decode()` on the bytestring before passing it to `reverse()`.

### 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 `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`.
- To enable support for [`Window`](/zh-hans/4.1/ref/models/expressions/#django.db.models.expressions.Window)
  expressions, set `DatabaseFeatures.supports_over_clause` to `True`. You
  may need to customize the `DatabaseOperations.window_start_rows_start_end()`
  and/or `window_start_range_start_end()` methods.
- Third-party database backends should add a
  `DatabaseOperations.cast_char_field_without_max_length` attribute with the
  database data type that will be used in the
  [`Cast`](/zh-hans/4.1/ref/models/database-functions/#django.db.models.functions.Cast) function for a `CharField` if the
  `max_length` argument isn't provided.
- The first argument of `DatabaseCreation._clone_test_db()` and
  `get_test_db_clone_settings()` is now `suffix` rather
  than `number` (in case you want to rename the signatures in your backend
  for consistency). `django.test` also now passes those values as strings
  rather than as integers.
- Third-party database backends should add a
  `DatabaseIntrospection.get_sequences()` method based on the stub in
  `BaseDatabaseIntrospection`.

### 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
[`DATABASES`](/zh-hans/4.1/ref/settings/#std-setting-DATABASES) setting to [use a different isolation level](/zh-hans/4.1/ref/databases/#mysql-isolation-level), if needed.

### [`AbstractUser.last_name`](/zh-hans/4.1/ref/contrib/auth/#django.contrib.auth.models.User.last_name) `max_length` increased to 150

A migration for [`django.contrib.auth.models.User.last_name`](/zh-hans/4.1/ref/contrib/auth/#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)
```

如果你想在管理中编辑用户时保留这个限制，请将 `UserAdmin.form` 设置为使用这个表单：

```
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

例子：

```
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.

In addition, because of a table alteration limitation of SQLite, it's prohibited
to perform [`RenameModel`](/zh-hans/4.1/ref/migration-operations/#django.db.migrations.operations.RenameModel) and
[`RenameField`](/zh-hans/4.1/ref/migration-operations/#django.db.migrations.operations.RenameField) operations on models or
fields referenced by other models in a transaction. In order to allow migrations
containing these operations to be applied, you must set the
`Migration.atomic` attribute to `False`.

### 杂项

- 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.
- [`RedirectView`](/zh-hans/4.1/ref/class-based-views/base/#django.views.generic.base.RedirectView) no longer silences
  `NoReverseMatch` if the `pattern_name` doesn't exist.
- When `USE_L10N` is off, [`FloatField`](/zh-hans/4.1/ref/forms/fields/#django.forms.FloatField) and
  [`DecimalField`](/zh-hans/4.1/ref/forms/fields/#django.forms.DecimalField) now respect [`DECIMAL_SEPARATOR`](/zh-hans/4.1/ref/settings/#std-setting-DECIMAL_SEPARATOR)
  and [`THOUSAND_SEPARATOR`](/zh-hans/4.1/ref/settings/#std-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 [`AbstractBaseUser`](/zh-hans/4.1/topics/auth/customizing/#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.
- [`assertNumQueries()`](/zh-hans/4.1/topics/testing/tools/#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 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,
  [`QuerySet.iterator()`](/zh-hans/4.1/ref/models/querysets/#django.db.models.query.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
  [`JavaScriptCatalog`](/zh-hans/4.1/topics/i18n/translation/#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 [automatic spatial transformations](/zh-hans/4.1/ref/contrib/gis/tutorial/#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 [preserve
  the relative order of elements in each list](/zh-hans/4.1/topics/forms/media/#form-media-asset-order).
  `MediaOrderConflictWarning` is issued if the order can't be preserved.
- `django.contrib.gis.gdal.OGRException` is removed. It's been an alias for
  `GDALException` since Django 1.8.
- Support for GEOS 3.3.x is dropped.
- The way data is selected for `GeometryField` is changed to improve
  performance, and in raw SQL queries, those fields must now be wrapped in
  `connection.ops.select`. See the [Raw queries note](/zh-hans/4.1/ref/contrib/gis/tutorial/#gis-raw-sql) in
  the GIS tutorial for an example.

## 在 2.0 中被废弃的功能

### `context` argument of `Field.from_db_value()` and `Expression.convert_value()`

The `context` argument of `Field.from_db_value()` and
`Expression.convert_value()` is unused as it's always an empty dictionary.
The signature of both methods is now:

```
(self, value, expression, connection)
```

替换成：

```
(self, value, expression, connection, context)
```

Support for the old signature in custom fields and expressions remains until
Django 3.0.

### 杂项

- 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
  [`django.shortcuts.render()`](/zh-hans/4.1/topics/http/shortcuts/#django.shortcuts.render). `render()` takes the same arguments
  except that it also requires a `request`.
- The `DEFAULT_CONTENT_TYPE` setting is deprecated. It doesn't interact 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.
- The `field_name` keyword argument to [`QuerySet.earliest()`](/zh-hans/4.1/ref/models/querysets/#django.db.models.query.QuerySet.earliest) and
  [`QuerySet.latest()`](/zh-hans/4.1/ref/models/querysets/#django.db.models.query.QuerySet.latest) is deprecated in favor of passing the field
  names as arguments. Write `.earliest('pub_date')` instead of
  `.earliest(field_name='pub_date')`.

## Features removed in 2.0

These features have reached the end of their deprecation cycle and are removed
in Django 2.0.

See [在 1.9 中被废弃的功能](/zh-hans/4.1/releases/1.9/#deprecated-features-1-9) for details on these changes, 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` is now
  required in models and migrations. Consider squashing migrations so that you
  have fewer of them to update.
- `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.

See [在 1.10 中被废弃的功能](/zh-hans/4.1/releases/1.10/#deprecated-features-1-10) for details on these changes.

- 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 in favor of its new
  location, `django.urls`.
- `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.