mirror of
https://github.com/django/django.git
synced 2024-12-25 02:26:12 +00:00
448 lines
16 KiB
Plaintext
448 lines
16 KiB
Plaintext
======================
|
|
The messages framework
|
|
======================
|
|
|
|
.. module:: django.contrib.messages
|
|
:synopsis: Provides cookie- and session-based temporary message storage.
|
|
|
|
Quite commonly in web applications, you need to display a one-time
|
|
notification message (also known as "flash message") to the user after
|
|
processing a form or some other types of user input.
|
|
|
|
For this, Django provides full support for cookie- and session-based
|
|
messaging, for both anonymous and authenticated users. The messages framework
|
|
allows you to temporarily store messages in one request and retrieve them for
|
|
display in a subsequent request (usually the next one). Every message is
|
|
tagged with a specific ``level`` that determines its priority (e.g., ``info``,
|
|
``warning``, or ``error``).
|
|
|
|
Enabling messages
|
|
=================
|
|
|
|
Messages are implemented through a :doc:`middleware </ref/middleware>`
|
|
class and corresponding :doc:`context processor </ref/templates/api>`.
|
|
|
|
The default ``settings.py`` created by ``django-admin.py startproject``
|
|
already contains all the settings required to enable message functionality:
|
|
|
|
* ``'django.contrib.messages'`` is in :setting:`INSTALLED_APPS`.
|
|
|
|
* :setting:`MIDDLEWARE_CLASSES` contains
|
|
``'django.contrib.sessions.middleware.SessionMiddleware'`` and
|
|
``'django.contrib.messages.middleware.MessageMiddleware'``.
|
|
|
|
The default :ref:`storage backend <message-storage-backends>` relies on
|
|
:doc:`sessions </topics/http/sessions>`. That's why ``SessionMiddleware``
|
|
must be enabled and appear before ``MessageMiddleware`` in
|
|
:setting:`MIDDLEWARE_CLASSES`.
|
|
|
|
* :setting:`TEMPLATE_CONTEXT_PROCESSORS` contains
|
|
``'django.contrib.messages.context_processors.messages'``.
|
|
|
|
If you don't want to use messages, you can remove
|
|
``'django.contrib.messages'`` from your :setting:`INSTALLED_APPS`, the
|
|
``MessageMiddleware`` line from :setting:`MIDDLEWARE_CLASSES`, and the
|
|
``messages`` context processor from :setting:`TEMPLATE_CONTEXT_PROCESSORS`.
|
|
|
|
Configuring the message engine
|
|
==============================
|
|
|
|
.. _message-storage-backends:
|
|
|
|
Storage backends
|
|
----------------
|
|
|
|
The messages framework can use different backends to store temporary messages.
|
|
|
|
Django provides three built-in storage classes in
|
|
:mod:`django.contrib.messages`:
|
|
|
|
.. class:: storage.session.SessionStorage
|
|
|
|
This class stores all messages inside of the request's session. Therefore
|
|
it requires Django's ``contrib.sessions`` application.
|
|
|
|
.. class:: storage.cookie.CookieStorage
|
|
|
|
This class stores the message data in a cookie (signed with a secret hash
|
|
to prevent manipulation) to persist notifications across requests. Old
|
|
messages are dropped if the cookie data size would exceed 2048 bytes.
|
|
|
|
.. class:: storage.fallback.FallbackStorage
|
|
|
|
This class first uses ``CookieStorage``, and falls back to using
|
|
``SessionStorage`` for the messages that could not fit in a single cookie.
|
|
It also requires Django's ``contrib.sessions`` application.
|
|
|
|
This behavior avoids writing to the session whenever possible. It should
|
|
provide the best performance in the general case.
|
|
|
|
:class:`~django.contrib.messages.storage.fallback.FallbackStorage` is the
|
|
default storage class. If it isn't suitable to your needs, you can select
|
|
another storage class by setting :setting:`MESSAGE_STORAGE` to its full import
|
|
path, for example::
|
|
|
|
MESSAGE_STORAGE = 'django.contrib.messages.storage.cookie.CookieStorage'
|
|
|
|
.. class:: storage.base.BaseStorage
|
|
|
|
To write your own storage class, subclass the ``BaseStorage`` class in
|
|
``django.contrib.messages.storage.base`` and implement the ``_get`` and
|
|
``_store`` methods.
|
|
|
|
.. _message-level:
|
|
|
|
Message levels
|
|
--------------
|
|
|
|
The messages framework is based on a configurable level architecture similar
|
|
to that of the Python logging module. Message levels allow you to group
|
|
messages by type so they can be filtered or displayed differently in views and
|
|
templates.
|
|
|
|
The built-in levels, which can be imported from ``django.contrib.messages``
|
|
directly, are:
|
|
|
|
=========== ========
|
|
Constant Purpose
|
|
=========== ========
|
|
``DEBUG`` Development-related messages that will be ignored (or removed) in a production deployment
|
|
``INFO`` Informational messages for the user
|
|
``SUCCESS`` An action was successful, e.g. "Your profile was updated successfully"
|
|
``WARNING`` A failure did not occur but may be imminent
|
|
``ERROR`` An action was **not** successful or some other failure occurred
|
|
=========== ========
|
|
|
|
The :setting:`MESSAGE_LEVEL` setting can be used to change the minimum recorded level
|
|
(or it can be `changed per request`_). Attempts to add messages of a level less
|
|
than this will be ignored.
|
|
|
|
.. _`changed per request`: `Changing the minimum recorded level per-request`_
|
|
|
|
Message tags
|
|
------------
|
|
|
|
Message tags are a string representation of the message level plus any
|
|
extra tags that were added directly in the view (see
|
|
`Adding extra message tags`_ below for more details). Tags are stored in a
|
|
string and are separated by spaces. Typically, message tags
|
|
are used as CSS classes to customize message style based on message type. By
|
|
default, each level has a single tag that's a lowercase version of its own
|
|
constant:
|
|
|
|
============== ===========
|
|
Level Constant Tag
|
|
============== ===========
|
|
``DEBUG`` ``debug``
|
|
``INFO`` ``info``
|
|
``SUCCESS`` ``success``
|
|
``WARNING`` ``warning``
|
|
``ERROR`` ``error``
|
|
============== ===========
|
|
|
|
To change the default tags for a message level (either built-in or custom),
|
|
set the :setting:`MESSAGE_TAGS` setting to a dictionary containing the levels
|
|
you wish to change. As this extends the default tags, you only need to provide
|
|
tags for the levels you wish to override::
|
|
|
|
from django.contrib.messages import constants as messages
|
|
MESSAGE_TAGS = {
|
|
messages.INFO: '',
|
|
50: 'critical',
|
|
}
|
|
|
|
Using messages in views and templates
|
|
=====================================
|
|
|
|
.. function:: add_message(request, level, message, extra_tags='', fail_silently=False)
|
|
|
|
Adding a message
|
|
----------------
|
|
|
|
To add a message, call::
|
|
|
|
from django.contrib import messages
|
|
messages.add_message(request, messages.INFO, 'Hello world.')
|
|
|
|
Some shortcut methods provide a standard way to add messages with commonly
|
|
used tags (which are usually represented as HTML classes for the message)::
|
|
|
|
messages.debug(request, '%s SQL statements were executed.' % count)
|
|
messages.info(request, 'Three credits remain in your account.')
|
|
messages.success(request, 'Profile details updated.')
|
|
messages.warning(request, 'Your account expires in three days.')
|
|
messages.error(request, 'Document deleted.')
|
|
|
|
.. _message-displaying:
|
|
|
|
Displaying messages
|
|
-------------------
|
|
.. function:: get_messages(request)
|
|
|
|
**In your template**, use something like::
|
|
|
|
{% if messages %}
|
|
<ul class="messages">
|
|
{% for message in messages %}
|
|
<li{% if message.tags %} class="{{ message.tags }}"{% endif %}>{{ message }}</li>
|
|
{% endfor %}
|
|
</ul>
|
|
{% endif %}
|
|
|
|
If you're using the context processor, your template should be rendered with a
|
|
``RequestContext``. Otherwise, ensure ``messages`` is available to
|
|
the template context.
|
|
|
|
Even if you know there is only just one message, you should still iterate over
|
|
the ``messages`` sequence, because otherwise the message storage will not be cleared
|
|
for the next request.
|
|
|
|
.. versionadded:: 1.7
|
|
|
|
The context processor also provides a ``DEFAULT_MESSAGE_LEVELS`` variable which
|
|
is a mapping of the message level names to their numeric value::
|
|
|
|
{% if messages %}
|
|
<ul class="messages">
|
|
{% for message in messages %}
|
|
<li{% if message.tags %} class="{{ message.tags }}"{% endif %}>
|
|
{% if message.level == DEFAULT_MESSAGE_LEVELS.ERROR %}Important: {% endif %}
|
|
{{ message }}
|
|
</li>
|
|
{% endfor %}
|
|
</ul>
|
|
{% endif %}
|
|
|
|
|
|
|
|
**Outside of templates**, you can use
|
|
:func:`~django.contrib.messages.get_messages`::
|
|
|
|
from django.contrib.messages import get_messages
|
|
|
|
storage = get_messages(request)
|
|
for message in storage:
|
|
do_something_with_the_message(message)
|
|
|
|
For instance, you can fetch all the messages to return them in a
|
|
:ref:`JSONResponseMixin <jsonresponsemixin-example>` instead of a
|
|
:class:`~django.views.generic.base.TemplateResponseMixin`.
|
|
|
|
:func:`~django.contrib.messages.get_messages` will return an
|
|
instance of the configured storage backend.
|
|
|
|
|
|
The ``Message`` class
|
|
---------------------
|
|
|
|
.. class:: storage.base.Message
|
|
|
|
When you loop over the list of messages in a template, what you get are
|
|
instances of the ``Message`` class. It's quite a simple object, with only a
|
|
few attributes:
|
|
|
|
* ``message``: The actual text of the message.
|
|
|
|
* ``level``: An integer describing the type of the message (see the
|
|
`message levels`_ section above).
|
|
|
|
* ``tags``: A string combining all the message's tags (``extra_tags`` and
|
|
``level_tag``) separated by spaces.
|
|
|
|
* ``extra_tags``: A string containing custom tags for this message,
|
|
separated by spaces. It's empty by default.
|
|
|
|
.. versionadded:: 1.7
|
|
|
|
* ``level_tag``: The string representation of the level. By default, it's
|
|
the lowercase version of the name of the associated constant, but this
|
|
can be changed if you need by using the :setting:`MESSAGE_TAGS` setting.
|
|
|
|
Creating custom message levels
|
|
------------------------------
|
|
|
|
Messages levels are nothing more than integers, so you can define your own
|
|
level constants and use them to create more customized user feedback, e.g.::
|
|
|
|
CRITICAL = 50
|
|
|
|
def my_view(request):
|
|
messages.add_message(request, CRITICAL, 'A serious error occurred.')
|
|
|
|
When creating custom message levels you should be careful to avoid overloading
|
|
existing levels. The values for the built-in levels are:
|
|
|
|
.. _message-level-constants:
|
|
|
|
============== =====
|
|
Level Constant Value
|
|
============== =====
|
|
``DEBUG`` 10
|
|
``INFO`` 20
|
|
``SUCCESS`` 25
|
|
``WARNING`` 30
|
|
``ERROR`` 40
|
|
============== =====
|
|
|
|
If you need to identify the custom levels in your HTML or CSS, you need to
|
|
provide a mapping via the :setting:`MESSAGE_TAGS` setting.
|
|
|
|
.. note::
|
|
If you are creating a reusable application, it is recommended to use
|
|
only the built-in `message levels`_ and not rely on any custom levels.
|
|
|
|
Changing the minimum recorded level per-request
|
|
-----------------------------------------------
|
|
|
|
The minimum recorded level can be set per request via the ``set_level``
|
|
method::
|
|
|
|
from django.contrib import messages
|
|
|
|
# Change the messages level to ensure the debug message is added.
|
|
messages.set_level(request, messages.DEBUG)
|
|
messages.debug(request, 'Test message...')
|
|
|
|
# In another request, record only messages with a level of WARNING and higher
|
|
messages.set_level(request, messages.WARNING)
|
|
messages.success(request, 'Your profile was updated.') # ignored
|
|
messages.warning(request, 'Your account is about to expire.') # recorded
|
|
|
|
# Set the messages level back to default.
|
|
messages.set_level(request, None)
|
|
|
|
Similarly, the current effective level can be retrieved with ``get_level``::
|
|
|
|
from django.contrib import messages
|
|
current_level = messages.get_level(request)
|
|
|
|
For more information on how the minimum recorded level functions, see
|
|
`Message levels`_ above.
|
|
|
|
Adding extra message tags
|
|
-------------------------
|
|
|
|
For more direct control over message tags, you can optionally provide a string
|
|
containing extra tags to any of the add methods::
|
|
|
|
messages.add_message(request, messages.INFO, 'Over 9000!',
|
|
extra_tags='dragonball')
|
|
messages.error(request, 'Email box full', extra_tags='email')
|
|
|
|
Extra tags are added before the default tag for that level and are space
|
|
separated.
|
|
|
|
Failing silently when the message framework is disabled
|
|
-------------------------------------------------------
|
|
|
|
If you're writing a reusable app (or other piece of code) and want to include
|
|
messaging functionality, but don't want to require your users to enable it
|
|
if they don't want to, you may pass an additional keyword argument
|
|
``fail_silently=True`` to any of the ``add_message`` family of methods. For
|
|
example::
|
|
|
|
messages.add_message(request, messages.SUCCESS, 'Profile details updated.',
|
|
fail_silently=True)
|
|
messages.info(request, 'Hello world.', fail_silently=True)
|
|
|
|
.. note::
|
|
Setting ``fail_silently=True`` only hides the ``MessageFailure`` that would
|
|
otherwise occur when the messages framework disabled and one attempts to
|
|
use one of the ``add_message`` family of methods. It does not hide failures
|
|
that may occur for other reasons.
|
|
|
|
Adding messages in Class Based Views
|
|
------------------------------------
|
|
|
|
.. class:: views.SuccessMessageMixin
|
|
|
|
Adds a success message attribute to
|
|
:class:`~django.views.generic.edit.FormView` based classes
|
|
|
|
.. method:: get_success_message(cleaned_data)
|
|
|
|
``cleaned_data`` is the cleaned data from the form which is used for
|
|
string formatting
|
|
|
|
**Example views.py**::
|
|
|
|
from django.contrib.messages.views import SuccessMessageMixin
|
|
from django.views.generic.edit import CreateView
|
|
from myapp.models import Author
|
|
|
|
class AuthorCreate(SuccessMessageMixin, CreateView):
|
|
model = Author
|
|
success_url = '/success/'
|
|
success_message = "%(name)s was created successfully"
|
|
|
|
The cleaned data from the ``form`` is available for string interpolation using
|
|
the ``%(field_name)s`` syntax. For ModelForms, if you need access to fields
|
|
from the saved ``object`` override the
|
|
:meth:`~django.contrib.messages.views.SuccessMessageMixin.get_success_message`
|
|
method.
|
|
|
|
**Example views.py for ModelForms**::
|
|
|
|
from django.contrib.messages.views import SuccessMessageMixin
|
|
from django.views.generic.edit import CreateView
|
|
from myapp.models import ComplicatedModel
|
|
|
|
class ComplicatedCreate(SuccessMessageMixin, CreateView):
|
|
model = ComplicatedModel
|
|
success_url = '/success/'
|
|
success_message = "%(calculated_field)s was created successfully"
|
|
|
|
def get_success_message(self, cleaned_data):
|
|
return self.success_message % dict(cleaned_data,
|
|
calculated_field=self.object.calculated_field)
|
|
|
|
Expiration of messages
|
|
======================
|
|
|
|
The messages are marked to be cleared when the storage instance is iterated
|
|
(and cleared when the response is processed).
|
|
|
|
To avoid the messages being cleared, you can set the messages storage to
|
|
``False`` after iterating::
|
|
|
|
storage = messages.get_messages(request)
|
|
for message in storage:
|
|
do_something_with(message)
|
|
storage.used = False
|
|
|
|
Behavior of parallel requests
|
|
=============================
|
|
|
|
Due to the way cookies (and hence sessions) work, **the behavior of any
|
|
backends that make use of cookies or sessions is undefined when the same
|
|
client makes multiple requests that set or get messages in parallel**. For
|
|
example, if a client initiates a request that creates a message in one window
|
|
(or tab) and then another that fetches any uniterated messages in another
|
|
window, before the first window redirects, the message may appear in the
|
|
second window instead of the first window where it may be expected.
|
|
|
|
In short, when multiple simultaneous requests from the same client are
|
|
involved, messages are not guaranteed to be delivered to the same window that
|
|
created them nor, in some cases, at all. Note that this is typically not a
|
|
problem in most applications and will become a non-issue in HTML5, where each
|
|
window/tab will have its own browsing context.
|
|
|
|
Settings
|
|
========
|
|
|
|
A few :ref:`settings<settings-messages>` give you control over message
|
|
behavior:
|
|
|
|
* :setting:`MESSAGE_LEVEL`
|
|
* :setting:`MESSAGE_STORAGE`
|
|
* :setting:`MESSAGE_TAGS`
|
|
|
|
.. versionadded:: 1.7
|
|
|
|
For backends that use cookies, the settings for the cookie are taken from
|
|
the session cookie settings:
|
|
|
|
* :setting:`SESSION_COOKIE_DOMAIN`
|
|
* :setting:`SESSION_COOKIE_SECURE`
|
|
* :setting:`SESSION_COOKIE_HTTPONLY`
|