django/docs/releases/1.4.txt

============================================
Django 1.4 release notes - UNDER DEVELOPMENT
============================================

This page documents release notes for the as-yet-unreleased Django
1.4. As such, it's tentative and subject to change. It provides
up-to-date information for those who are following trunk.

Django 1.4 includes various `new features`_ and some minor `backwards
incompatible changes`_. There are also some features that have been dropped,
which are detailed in :doc:`our deprecation plan </internals/deprecation>`.

.. _new features: `What's new in Django 1.4`_
.. _backwards incompatible changes: backwards-incompatible-changes-1.4_

What's new in Django 1.4
========================

``SELECT FOR UPDATE`` support
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Django 1.4 now includes a :meth:`QuerySet.select_for_update()
<django.db.models.query.QuerySet.select_for_update>` method which generates a
``SELECT ... FOR UPDATE`` SQL query. This will lock rows until the end of the
transaction, meaning that other transactions cannot modify or delete rows
matched by a ``FOR UPDATE`` query.

For more details, see the documentation for
:meth:`~django.db.models.query.QuerySet.select_for_update`.

HTML5
~~~~~

We've switched the admin and other bundled templates to use the HTML5
doctype. While Django will be careful in its use of HTML5 features, to maintain
compatibility with old browsers, this change means that you can use any HTML5
features you need in admin pages without having to lose HTML validity or
override the provided templates to change the doctype.

List filters in admin interface
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Prior to Django 1.4, the Django admin app allowed specifying change list
filters by specifying a field lookup (including spanning relations), and
not custom filters. This has been rectified with a simple API previously
known as "FilterSpec" which was used internally. For more details, see the
documentation for :attr:`~django.contrib.admin.ModelAdmin.list_filter`.

``reverse_lazy``
~~~~~~~~~~~~~~~~

A lazily evaluated version of :func:`django.core.urlresolvers.reverse` was
added to allow using URL reversals before the project's URLConf gets loaded.

Assignment template tags
~~~~~~~~~~~~~~~~~~~~~~~~

A new helper function,
:ref:`assignment_tag<howto-custom-template-tags-assignment-tags>`, was added to
``template.Library`` to ease the creation of template tags that store some
data in a specified context variable.

.. _backwards-incompatible-changes-1.4:

Backwards incompatible changes in 1.4
=====================================

Compatibility with old signed data
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Django 1.3 changed the cryptographic signing mechanisms used in a number of
places in Django. While Django 1.3 kept fallbacks that would accept hashes
produced by the previous methods, these fallbacks are removed in Django 1.4.

So, if you upgrade to Django 1.4 directly from 1.2 or earlier, you may
lose/invalidate certain pieces of data that have been cryptographically signed
using an old method. To avoid this, use Django 1.3 first, for a period of time,
to allow the signed data to expire naturally. The affected parts are detailed
below, with 1) the consequences of ignoring this advice and 2) the amount of
time you need to run Django 1.3 for the data to expire or become irrelevant.

* contrib.sessions data integrity check

  * consequences: the user will be logged out, and session data will be lost.

  * time period: defined by SESSION_COOKIE_AGE.

* contrib.auth password reset hash

  * consequences: password reset links from before the upgrade will not work.

  * time period: defined by PASSWORD_RESET_TIMEOUT_DAYS.

Form related hashes — these are much shorter lifetime, and are relevant only for
the short window where a user might fill in a form generated by the pre-upgrade
Django instance, and try to submit it to the upgraded Django instance:

* contrib.comments form security hash

  * consequences: the user will see a validation error "Security hash failed".

  * time period: the amount of time you expect users to take filling out comment
    forms.

* FormWizard security hash

  * consequences: the user will see an error about the form having expired,
    and will be sent back to the first page of the wizard, losing the data
    they have inputted so far.

  * time period: the amount of time you expect users to take filling out the
    affected forms.

* CSRF check

  * Note: This is actually a Django 1.1 fallback, not Django 1.2,
    and applies only if you are upgrading from 1.1.

  * consequences: the user will see a 403 error with any CSRF protected POST
    form.

  * time period: the amount of time you expect user to take filling out
    such forms.

django.contrib.flatpages
~~~~~~~~~~~~~~~~~~~~~~~~

Starting in the 1.4 release the
:class:`~django.contrib.flatpages.middleware.FlatpageFallbackMiddleware` only
adds a trailing slash and redirects if the resulting URL refers to an existing
flatpage. For example, requesting ``/notaflatpageoravalidurl`` in a previous
version would redirect to ``/notaflatpageoravalidurl/``, which would
subsequently raise a 404. Requesting ``/notaflatpageoravalidurl`` now will
immediately raise a 404. Additionally redirects returned by flatpages are now
permanent (301 status code) to match the behaviour of the
:class:`~django.middleware.common.CommonMiddleware`.

`COMMENTS_BANNED_USERS_GROUP` setting
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Django's :doc:`comments app </ref/contrib/comments/index>` has historically
supported excluding the comments of a special user group but never documented
the feature properly and didn't enforce the exclusion in other parts of the
app, e.g. the template tags. To fix this problem the code was removed from
the feed class.

If you rely on the feature and want to restore the old behaviour, simply use
a custom comment model manager to exclude the user group, e.g.::

    from django.conf import settings
    from django.contrib.comments.managers import CommentManager

    class BanningCommentManager(CommentManager):

        def get_query_set(self):
            qs = super(BanningCommentManager, self).get_query_set()
            if getattr(settings, 'COMMENTS_BANNED_USERS_GROUP', None):
                where = ['user_id NOT IN (SELECT user_id FROM auth_user_groups WHERE group_id = %s)']
                params = [settings.COMMENTS_BANNED_USERS_GROUP]
                qs = qs.extra(where=where, params=params)
            return qs

Save this model manager in your custom comment app (e.g. in
``my_comments_app/managers.py``) and add it your
:ref:`custom comment app model <custom-comment-app-api>`::

    from django.db import models
    from django.contrib.comments.models import Comment

    from my_comments_app.managers import BanningCommentManager

    class CommentWithTitle(Comment):
        title = models.CharField(max_length=300)

        objects = BanningCommentManager()

For more details see the docs about
:doc:`customizing the comments framework </ref/contrib/comments/custom>`.

`IGNORABLE_404_STARTS` and `IGNORABLE_404_ENDS` settings
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Django can report 404 errors: see :doc:`/howto/error-reporting`.
Until Django 1.3, it was possible to exclude some URLs from the reporting
by adding prefixes to :setting:`IGNORABLE_404_STARTS` and suffixes to
:setting:`IGNORABLE_404_ENDS`.

In Django 1.4, these two settings are superseded by
:setting:`IGNORABLE_404_URLS`, which is a list of compiled regular expressions.
Django won't send an email for 404 errors on URLs that match any of them.

Furthermore, the previous settings had some rather arbitrary default values::

    IGNORABLE_404_STARTS = ('/cgi-bin/', '/_vti_bin', '/_vti_inf')
    IGNORABLE_404_ENDS = ('mail.pl', 'mailform.pl', 'mail.cgi', 'mailform.cgi',
                          'favicon.ico', '.php')

It's not Django's role to decide if your website has a legacy ``/cgi-bin/``
section or a ``favicon.ico``. As a consequence, the default values of
:setting:`IGNORABLE_404_URLS`, :setting:`IGNORABLE_404_STARTS` and
:setting:`IGNORABLE_404_ENDS` are all now empty.

If you have customized :setting:`IGNORABLE_404_STARTS` or
:setting:`IGNORABLE_404_ENDS`, or if you want to keep the old default value,
you should add the following lines in your settings file::

    import re
    IGNORABLE_404_URLS = (
        # for each <prefix> in IGNORABLE_404_STARTS
        re.compile(r'^<prefix>'),
        # for each <suffix> in IGNORABLE_404_ENDS
        re.compile(r'<suffix>$'),
    )

Don't forget to escape characters that have a special meaning in a regular
expression.