====================== The messages framework ====================== .. module:: django.contrib.messages :synopsis: Provides cookie- and session-based temporary message storage. Django provides full support for cookie- and session-based messaging, for both anonymous and authenticated clients. 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``). .. versionadded:: 1.2 The messages framework was added. Enabling messages ================= Messages are implemented through a :doc:`middleware ` class and corresponding :doc:`context processor `. To enable message functionality, do the following: * Edit the :setting:`MIDDLEWARE_CLASSES` setting and make sure it contains ``'django.contrib.messages.middleware.MessageMiddleware'``. If you are using a :ref:`storage backend ` that relies on :doc:`sessions ` (the default), ``'django.contrib.sessions.middleware.SessionMiddleware'`` must be enabled and appear before ``MessageMiddleware`` in your :setting:`MIDDLEWARE_CLASSES`. * Edit the :setting:`TEMPLATE_CONTEXT_PROCESSORS` setting and make sure it contains ``'django.contrib.messages.context_processors.messages'``. * Add ``'django.contrib.messages'`` to your :setting:`INSTALLED_APPS` setting The default ``settings.py`` created by ``django-admin.py startproject`` has ``MessageMiddleware`` activated and the ``django.contrib.messages`` app installed. Also, the default value for :setting:`TEMPLATE_CONTEXT_PROCESSORS` contains ``'django.contrib.messages.context_processors.messages'``. If you don't want to use messages, you can remove the ``MessageMiddleware`` line from :setting:`MIDDLEWARE_CLASSES`, the ``messages`` context processor from :setting:`TEMPLATE_CONTEXT_PROCESSORS` and ``'django.contrib.messages'`` from your :setting:`INSTALLED_APPS`. Configuring the message engine ============================== .. _message-storage-backends: Storage backends ---------------- The messages framework can use different backends to store temporary messages. To change which backend is being used, add a `MESSAGE_STORAGE`_ to your settings, referencing the module and class of the storage class. For example:: MESSAGE_STORAGE = 'django.contrib.messages.storage.cookie.CookieStorage' The value should be the full path of the desired storage class. Four storage classes are included: ``'django.contrib.messages.storage.session.SessionStorage'`` This class stores all messages inside of the request's session. It requires Django's ``contrib.sessions`` application. ``'django.contrib.messages.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 4096 bytes. ``'django.contrib.messages.storage.fallback.FallbackStorage'`` This class first uses CookieStorage for all messages, falling back to using SessionStorage for the messages that could not fit in a single cookie. Since it is uses SessionStorage, it also requires Django's ``contrib.sessions`` application. To write your own storage class, subclass the ``BaseStorage`` class in ``django.contrib.messages.storage.base`` and implement the ``_get`` and ``_store`` methods. 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 `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 `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 ===================================== 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.') Displaying messages ------------------- In your template, use something like:: {% if messages %} {% 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. 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 `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) Internally, Django uses this functionality in the create, update, and delete :doc:`generic views ` so that they work even if the message framework is disabled. .. 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. 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 :doc:`Django settings ` give you control over message behavior: MESSAGE_LEVEL ------------- Default: ``messages.INFO`` This sets the minimum message that will be saved in the message storage. See `Message levels`_ above for more details. .. admonition:: Important If you override ``MESSAGE_LEVEL`` in your settings file and rely on any of the built-in constants, you must import the constants module directly to avoid the potential for circular imports, e.g.:: from django.contrib.messages import constants as message_constants MESSAGE_LEVEL = message_constants.DEBUG If desired, you may specify the numeric values for the constants directly according to the values in the above :ref:`constants table `. MESSAGE_STORAGE --------------- Default: ``'django.contrib.messages.storage.user_messages.FallbackStorage'`` Controls where Django stores message data. Valid values are: * ``'django.contrib.messages.storage.fallback.FallbackStorage'`` * ``'django.contrib.messages.storage.session.SessionStorage'`` * ``'django.contrib.messages.storage.cookie.CookieStorage'`` See `Storage backends`_ for more details. MESSAGE_TAGS ------------ Default:: {messages.DEBUG: 'debug', messages.INFO: 'info', messages.SUCCESS: 'success', messages.WARNING: 'warning', messages.ERROR: 'error',} This sets the mapping of message level to message tag, which is typically rendered as a CSS class in HTML. If you specify a value, it will extend the default. This means you only have to specify those values which you need to override. See `Displaying messages`_ above for more details. .. admonition:: Important If you override ``MESSAGE_TAGS`` in your settings file and rely on any of the built-in constants, you must import the ``constants`` module directly to avoid the potential for circular imports, e.g.:: from django.contrib.messages import constants as message_constants MESSAGE_TAGS = {message_constants.INFO: ''} If desired, you may specify the numeric values for the constants directly according to the values in the above :ref:`constants table `. SESSION_COOKIE_DOMAIN --------------------- Default: ``None`` The storage backends that use cookies -- ``CookieStorage`` and ``FallbackStorage`` -- use the value of :setting:`SESSION_COOKIE_DOMAIN` in setting their cookies. See the :doc:`settings documentation ` for more information on how this works and why you might need to set it. .. _Django settings: ../settings/