在Python的Django框架的视图中使用Session的方法
SessionMiddleware 激活后，每个传给视图(view)函数的第一个参数``HttpRequest`` 对象都有一个 session 属性，这是一个字典型的对象。 你可以象用普通字典一样来用它。 例如，在视图(view)中你可以这样用：
# Set a session value: request.session["fav_color"] = "blue" # Get a session value -- this could be called in a different view, # or many requests later (or both): fav_color = request.session["fav_color"] # Clear an item from the session: del request.session["fav_color"] # Check if the session has a given key: if "fav_color" in request.session: ...
其他的映射方法，如 keys() 和 items() 对 request.session 同样有效：
下面是一些有效使用Django sessions的简单规则：
用正常的字符串作为key来访问字典 request.session ， 而不是整数、对象或其它什么的。
Session字典中以下划线开头的key值是Django内部保留key值。 框架只会用很少的几个下划线 开头的session变量，除非你知道他们的具体含义，而且愿意跟上Django的变化，否则，最好 不要用这些下划线开头的变量，它们会让Django搅乱你的应用。
比如，不要象这样使用`` _fav_color`` 会话密钥(session key)：
request.session['_fav_color'] = 'blue' # Don't do this!
不要用一个新对象来替换掉 request.session ，也不要存取其属性。 可以像Python中的字典那样使用。 例如：
request.session = some_other_object # Don't do this! request.session.foo = 'bar' # Don't do this!
我们来看个简单的例子。 这是个简单到不能再简单的例子：在用户发了一次评论后将has_commented设置为True。 这是个简单（但不很安全）的、防止用户多次评论的方法。
def post_comment(request):
if request.method != 'POST':
raise Http404('Only POSTs are allowed')
if 'comment' not in request.POST:
raise Http404('Comment not submitted')
if request.session.get('has_commented', False):
return HttpResponse("You've already commented.")
c = comments.Comment(comment=request.POST['comment'])
c.save()
request.session['has_commented'] = True
return HttpResponse('Thanks for your comment!')
下面是一个很简单的站点登录视图(view)：
def login(request):
if request.method != 'POST':
raise Http404('Only POSTs are allowed')
try:
m = Member.objects.get(username=request.POST['username'])
if m.password == request.POST['password']:
request.session['member_id'] = m.id
return HttpResponseRedirect('/you-are-logged-in/')
except Member.DoesNotExist:
return HttpResponse("Your username and password didn't match.")
下面的例子将登出一个在上面已通过`` login()`` 登录的用户：
def logout(request):
try:
del request.session['member_id']
except KeyError:
pass
return HttpResponse("You're logged out.")
注意
在实践中，这是很烂的用户登录方式，稍后讨论的认证(authentication )框架会帮你以更健壮和有利的方式来处理这些问题。 这些非常简单的例子只是想让你知道这一切是如何工作的。 这些实例尽量简单，这样你可以更容易看到发生了什么
设置测试Cookies
就像前面提到的，你不能指望所有的浏览器都可以接受cookie。 因此，为了使用方便，Django提供了一个简单的方法来测试用户的浏览器是否接受cookie。 你只需在视图(view)中调用 request.session.set_test_cookie()，并在后续的视图(view)、而不是当前的视图(view)中检查 request.session.test_cookie_worked() 。
虽然把 set_test_cookie() 和 test_cookie_worked() 分开的做法看起来有些笨拙，但由于cookie的工作方式，这无可避免。 当设置一个cookie时候，只能等浏览器下次访问的时候，你才能知道浏览器是否接受cookie。
检查cookie是否可以正常工作后，你得自己用 delete_test_cookie() 来清除它，这是个好习惯。 在你证实了测试cookie已工作了之后这样操作。
这是个典型例子：
def login(request):
# If we submitted the form...
if request.method == 'POST':
# Check that the test cookie worked (we set it below):
if request.session.test_cookie_worked():
# The test cookie worked, so delete it.
request.session.delete_test_cookie()
# In practice, we'd need some logic to check username/password
# here, but since this is an example...
return HttpResponse("You're logged in.")
# The test cookie failed, so display an error message. If this
# were a real site, we'd want to display a friendlier message.
else:
return HttpResponse("Please enable cookies and try again.")
# If we didn't post, send the test cookie along with the login form.
request.session.set_test_cookie()
return render_to_response('foo/login_form.html')
注意
再次强调，内置的认证函数会帮你做检查的。
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