=================== How to use sessions =================== Django provides full support for anonymous sessions. The session framework lets you store and retrieve arbitrary data on a per-site-visitor basis. It stores data on the server side and abstracts the sending and receiving of cookies. Cookies contain a session ID -- not the data itself. Enabling sessions ================= Session functionality is enabled by default. You can turn session functionality on and off by editing the ``MIDDLEWARE_CLASSES`` setting. To activate sessions, make sure ``MIDDLEWARE_CLASSES`` contains ``"django.contrib.sessions.middleware.SessionMiddleware"``. If you don't want to use sessions, you might as well remove the ``SessionMiddleware`` line from ``MIDDLEWARE_CLASSES``. It'll save you a small bit of overhead. Using sessions in views ======================= Each ``HttpRequest`` object -- the first argument to any Django view function -- has a ``session`` attribute, which is a dictionary-like object. You can read it and write to it. It implements the following standard dictionary methods: * ``__contains__(key)`` Example: ``'fav_color' in request.session`` * ``__getitem__(key)`` Example: ``fav_color = request.session['fav_color']`` * ``__setitem__(key, value)`` Example: ``request.session['fav_color'] = 'blue'`` * ``__delitem__(key)`` Example: ``del request.session['fav_color']``. This raises ``KeyError`` if the given ``key`` isn't already in the session. * ``get(key, default=None)`` Example: ``fav_color = request.session.get('fav_color', 'red')`` * ``keys()`` **New in Django development version.** * ``items()`` **New in Django development version.** It also has these three methods: * ``set_test_cookie()`` Sets a test cookie to determine whether the user's browser supports cookies. Due to the way cookies work, you won't be able to test this until the user's next page request. See "Setting test cookies" below for more information. * ``test_cookie_worked()`` Returns either ``True`` or ``False``, depending on whether the user's browser accepted the test cookie. Due to the way cookies work, you'll have to call ``set_test_cookie()`` on a previous, separate page request. See "Setting test cookies" below for more information. * ``delete_test_cookie()`` Deletes the test cookie. Use this to clean up after yourself. You can edit ``request.session`` at any point in your view. You can edit it multiple times. Session object guidelines ------------------------- * Use normal Python strings as dictionary keys on ``request.session``. This is more of a convention than a hard-and-fast rule. * Session dictionary keys that begin with an underscore are reserved for internal use by Django. * Don't override ``request.session`` with a new object, and don't access or set its attributes. Use it like a Python dictionary. Examples -------- This simplistic view sets a ``has_commented`` variable to ``True`` after a user posts a comment. It doesn't let a user post a comment more than once:: def post_comment(request, new_comment): if request.session.get('has_commented', False): return HttpResponse("You've already commented.") c = comments.Comment(comment=new_comment) c.save() request.session['has_commented'] = True return HttpResponse('Thanks for your comment!') This simplistic view logs in a "member" of the site:: def login(request): m = members.get_object(username__exact=request.POST['username']) if m.password == request.POST['password']: request.session['member_id'] = m.id return HttpResponse("You're logged in.") else: return HttpResponse("Your username and password didn't match.") ...And this one logs a member out, according to ``login()`` above:: def logout(request): try: del request.session['member_id'] except KeyError: pass return HttpResponse("You're logged out.") Setting test cookies ==================== As a convenience, Django provides an easy way to test whether the user's browser accepts cookies. Just call ``request.session.set_test_cookie()`` in a view, and call ``request.session.test_cookie_worked()`` in a subsequent view -- not in the same view call. This awkward split between ``set_test_cookie()`` and ``test_cookie_worked()`` is necessary due to the way cookies work. When you set a cookie, you can't actually tell whether a browser accepted it until the browser's next request. It's good practice to use ``delete_test_cookie()`` to clean up after yourself. Do this after you've verified that the test cookie worked. Here's a typical usage example:: def login(request): if request.POST: if request.session.test_cookie_worked(): request.session.delete_test_cookie() return HttpResponse("You're logged in.") else: return HttpResponse("Please enable cookies and try again.") request.session.set_test_cookie() return render_to_response('foo/login_form') Using sessions out of views =========================== Internally, each session is just a normal Django model. The ``Session`` model is defined in ``django/contrib/sessions/models.py``. Because it's a normal model, you can access sessions using the normal Django database API:: >>> from django.contrib.sessions.models import Session >>> s = Session.objects.get_object(pk='2b1189a188b44ad18c35e113ac6ceead') >>> s.expire_date datetime.datetime(2005, 8, 20, 13, 35, 12) Note that you'll need to call ``get_decoded()`` to get the session dictionary. This is necessary because the dictionary is stored in an encoded format:: >>> s.session_data 'KGRwMQpTJ19hdXRoX3VzZXJfaWQnCnAyCkkxCnMuMTExY2ZjODI2Yj...' >>> s.get_decoded() {'user_id': 42} When sessions are saved ======================= By default, Django only saves to the session database when the session has been modified -- that is if any of its dictionary values have been assigned or deleted:: # Session is modified. request.session['foo'] = 'bar' # Session is modified. del request.session['foo'] # Session is modified. request.session['foo'] = {} # Gotcha: Session is NOT modified, because this alters # request.session['foo'] instead of request.session. request.session['foo']['bar'] = 'baz' To change this default behavior, set the ``SESSION_SAVE_EVERY_REQUEST`` setting to ``True``. If ``SESSION_SAVE_EVERY_REQUEST`` is ``True``, Django will save the session to the database on every single request. Note that the session cookie is only sent when a session has been created or modified. If ``SESSION_SAVE_EVERY_REQUEST`` is ``True``, the session cookie will be sent on every request. Similarly, the ``expires`` part of a session cookie is updated each time the session cookie is sent. Settings ======== A few `Django settings`_ give you control over session behavior: SESSION_COOKIE_AGE ------------------ Default: ``1209600`` (2 weeks, in seconds) The age of session cookies, in seconds. SESSION_COOKIE_DOMAIN --------------------- Default: ``None`` The domain to use for session cookies. Set this to a string such as ``".lawrence.com"`` for cross-domain cookies, or use ``None`` for a standard domain cookie. SESSION_COOKIE_NAME ------------------- Default: ``'sessionid'`` The name of the cookie to use for sessions. This can be whatever you want. SESSION_SAVE_EVERY_REQUEST -------------------------- Default: ``False`` Whether to save the session data on every request. If this is ``False`` (default), then the session data will only be saved if it has been modified -- that is, if any of its dictionary values have been assigned or deleted. .. _Django settings: http://www.djangoproject.com/documentation/settings/ Technical details ================= * The session dictionary should accept any pickleable Python object. See `the pickle module`_ for more information. * Session data is stored in a database table named ``core_sessions`` . * Django only sends a cookie if it needs to. If you don't set any session data, it won't send a session cookie. .. _`the pickle module`: http://www.python.org/doc/current/lib/module-pickle.html Session IDs in URLs =================== The Django sessions framework is entirely, and solely, cookie-based. It does not fall back to putting session IDs in URLs as a last resort, as PHP does. This is an intentional design decision. Not only does that behavior make URLs ugly, it makes your site vulnerable to session-ID theft via the "Referer" header.