Django 2.0 release notes¶

Simplified URL routing syntax¶

The new django.urls.path() function allows a simpler, more readable URL routing syntax. For example, this example from previous Django releases:

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

could be written as:

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

The new syntax supports type coercion of URL parameters. In the example, the view will receive the year keyword argument as an integer rather than as a string. Also, the URLs that will match are slightly less constrained in the rewritten example. For example, the year 10000 will now match since the year integers aren’t constrained to be exactly four digits long as they are in the regular expression.

The django.conf.urls.url() function from previous versions is now available as django.urls.re_path(). The old location remains for backwards compatibility, without an imminent deprecation. The old django.conf.urls.include() function is now importable from django.urls so you can use from django.urls import include, path, re_path in your URLconfs.

The URL dispatcher document is rewritten to feature the new syntax and provide more details.

Mobile-friendly contrib.admin¶

The admin is now responsive and supports all major mobile devices. Older browsers may experience varying levels of graceful degradation.

Window expressions¶

The new Window expression allows adding an OVER clause to querysets. You can use window functions and aggregate functions in the expression.

Minor features¶

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 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().

Database backend API¶

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

• 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 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 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 setting to use a different isolation level, if needed.

AbstractUser.last_name max_length increased to 150¶

A migration for 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)

If you wish to keep this restriction in the admin when editing users, set UserAdmin.form to use this form:

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¶

For example:

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 and 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.

Miscellaneous¶

• 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 no longer silences NoReverseMatch if the pattern_name doesn’t exist.

• When USE_L10N is off, FloatField and DecimalField now respect DECIMAL_SEPARATOR and 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 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() 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() 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 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 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. 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 in the GIS tutorial for an example.

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)

instead of:

(self, value, expression, connection, context)

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

Miscellaneous¶

• 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(). 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() and QuerySet.latest() is deprecated in favor of passing the field names as arguments. Write .earliest('pub_date') instead of .earliest(field_name='pub_date').