django - 在没有太多复制/粘贴的情况下很好地重定向错误？

Question

如果我有处理 friend 管理的 View ，则意味着有一个 View 可以处理添加，删除，阻止，取消阻止以及接受/拒绝成为 friend 的邀请。我遇到的问题是，当我尝试向最终以不应该使用的URL结尾的用户提供有意义的错误时。

例如，如果 User1 和 User2 已经是 friend ，并且 User1 转到将 User2 作为 friend 添加的URL，而不是像他们不是 friend 一样显示表单，并且unique_together = (('user_from', 'user_to'),)上显示的表单失败警告消息，并在显示表单之前将它们重定向到适当的页面。

像这样

def add_friend(request, username):
    try:
        user = User.objects.get(username=username)
    except User.DoesNotExist:
        messages.error(request, 'A user with the username %s does not exist. \
            Try searching for the user below.' % username)
        return HttpResponseRedirect(reverse('friends_find_friend'))

    if Friend.objects.are_friends(request.user, user):
        messages.error(request, 'You are already friends with %s' % user)
        return HttpResponseRedirect(reverse('profiles_profile_detail', args=[user]))

如果没有这样的用户，它还包括检查和有意义的错误消息(而不是404)。

这很容易处理，但是随着其他检查的发展，

def add_friend(request, username):
    try:
        user = User.objects.get(username=username)
    except User.DoesNotExist:
        messages.error(request, 'A user with the username %s does not exist. \
            Try searching for the user below.' % username)
        return HttpResponseRedirect(reverse('friends_find_friend'))

    if user == request.user:
        messages.error(request, 'You are already friends with yourself')
        return HttpResponseRedirect(reverse('friends_find_friend'))

    if Enemy.objects.is_blocked(request.user, user):
        messages.error(request, '%s has blocked you from adding them as a friend' % user)
        return HttpResponseRedirect(reverse('friends_find_friend'))

    if Enemy.objects.has_blocked(request.user, user):
        messages.error(request, 'You have blocked %s so you cannot add them as a friend' % user)
        return HttpResponseRedirect(reverse('profiles_profile_detail', args=[user]))

    if Friend.objects.are_friends(request.user, user):
        messages.error(request, 'You are already friends with %s' % user)
        return HttpResponseRedirect(reverse('profiles_profile_detail', args=[user]))

    if FriendRequest.objects.invitation_sent(request.user, user):
        messages.error(request, 'You already sent %s a request. You need to \
            wait for them to reply to it.' % user)
        return HttpResponseRedirect(reverse('friends_pending'))

    if FriendRequest.objects.invitation_received(request.user, user):
        messages.error(request, '%s already sent you a request and is waiting \
            for you to respond to them.' % user)
        return HttpResponseRedirect(reverse('friends_pending'))

所有这些都在重复

remove_friend

block_user

unblock_user

未决邀请

如果在 shell 中绕过 View 并且独立使用表单，则还会进一步复制为表单验证错误。

我要问的是，是否有一种更Python的方式来完成此任务，而又不会过度复制和粘贴？

编辑:

我一直在试图解决这个问题，并且想知道这样的事情是否是个好方法。

tests = ((Enemy.objects.is_blocked, 'This user has blocked you', reverse('friends_find_friend')),
         (Enemy.objects.has_blocked, 'You have blocked this user', reverse('profiles_profile_detail', args=[user])),)

for test in tests:
    if test[0](request.user, user):
        messages.error(request, test[1])
        return HttpResponseRedirect(test[2])

测试将在类似于url模式的另一个文件中定义，并且装饰器将包装view函数以运行所有测试，如果一切失败，则重定向，如果一切正常，最后将其传递给view函数。这将是一种有效的方法，而不会阻塞数百行样板代码的 View 文件吗？

Edit2 :

我也很想看看别人如何做类似的事情。我怀疑我是第一个想要向用户显示消息而不是仅仅抛出404页面的人。

Answer 1

Python装饰器是完美的选择。

定义您在装饰器中执行的所有验证，并以此装饰所有add_friend，remove_friend等。

更新:

对于您的情况，它将看起来像这样:

def do_friending_validation(fun):
    def validate_function(*args,**kwargs):
        try:
            user = User.objects.get(username=username)
        except User.DoesNotExist:
            messages.error(request, 'A user with the username %s does not exist. \
                Try searching for the user below.' % username)
            return HttpResponseRedirect(reverse('friends_find_friend'))

        if user == request.user:
        messages.error(request, 'You are already friends with yourself')
        return HttpResponseRedirect(reverse('friends_find_friend'))

        if Enemy.objects.is_blocked(request.user, user):
        messages.error(request, '%s has blocked you from adding them as a friend' % user)
        return HttpResponseRedirect(reverse('friends_find_friend'))

        if Enemy.objects.has_blocked(request.user, user):
        messages.error(request, 'You have blocked %s so you cannot add them as a friend' % user)
        return HttpResponseRedirect(reverse('profiles_profile_detail', args=[user]))

        if Friend.objects.are_friends(request.user, user):
        messages.error(request, 'You are already friends with %s' % user)
        return HttpResponseRedirect(reverse('profiles_profile_detail', args=[user]))

        if FriendRequest.objects.invitation_sent(request.user, user):
        messages.error(request, 'You already sent %s a request. You need to \
            wait for them to reply to it.' % user)
        return HttpResponseRedirect(reverse('friends_pending'))

        if FriendRequest.objects.invitation_received(request.user, user):
        messages.error(request, '%s already sent you a request and is waiting \
            for you to respond to them.' % user)
        return HttpResponseRedirect(reverse('friends_pending'))
        fun(*args,**kwargs)

    return validate_function

@do_friending_validation
def add_friend(request, username):

    #Do your stuff here

@do_friending_validation    
def remove_friend(request, username):

    #Do your stuff here