python - 从 Django 1.4 升级到 1.6 后在管理中保存对象时列出索引超出范围错误

Question

我最近将 1.4 项目升级到 1.6，在解决了一些弃用问题后，我遇到了另一个我无法解决的问题。

每次我尝试保存新对象或编辑现有对象时，我都会收到 list index out of range错误。我理解错误的含义，但不知道 django 如何设置 obj 的值它的值应该是 obj[3]回溯将我发送到这里:django/contrib/messages/storage/cookie.py in process_messages, line 38

完整回溯:

   Traceback:
File "/Users/user/Development/virtual_environments/demo/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response
  201.                 response = middleware_method(request, response)
File "/Users/user/Development/virtual_environments/demo/lib/python2.7/site-packages/django/contrib/messages/middleware.py" in process_response
  23.             unstored_messages = request._messages.update(response)
File "/Users/user/Development/virtual_environments/demo/lib/python2.7/site-packages/django/contrib/messages/storage/base.py" in update
  140.             messages = self._loaded_messages + self._queued_messages
File "/Users/user/Development/virtual_environments/demo/lib/python2.7/site-packages/django/contrib/messages/storage/base.py" in _loaded_messages
  91.             messages, all_retrieved = self._get()
File "/Users/user/Development/virtual_environments/demo/lib/python2.7/site-packages/django/contrib/messages/storage/fallback.py" in _get
  24.             messages, all_retrieved = storage._get()
File "/Users/user/Development/virtual_environments/demo/lib/python2.7/site-packages/django/contrib/messages/storage/cookie.py" in _get
  70.         messages = self._decode(data)
File "/Users/user/Development/virtual_environments/demo/lib/python2.7/site-packages/django/contrib/messages/storage/cookie.py" in _decode
  154.                     return json.loads(value, cls=MessageDecoder)
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/__init__.py" in loads
  339.     return cls(encoding=encoding, **kw).decode(s)
File "/Users/user/Development/virtual_environments/demo/lib/python2.7/site-packages/django/contrib/messages/storage/cookie.py" in decode
  49.         return self.process_messages(decoded)
File "/Users/user/Development/virtual_environments/demo/lib/python2.7/site-packages/django/contrib/messages/storage/cookie.py" in process_messages
  41.             return [self.process_messages(item) for item in obj]
File "/Users/user/Development/virtual_environments/demo/lib/python2.7/site-packages/django/contrib/messages/storage/cookie.py" in process_messages
  38.                     print 'OBJECT 3: {0}'.format(obj[3])

来自 cookies.py 的代码。问题在于试图获取 obj[3]obj 的值为:[u'__json_message', 20, u'The Player "Goodman" was changed successfully.']

class MessageDecoder(json.JSONDecoder):                            
    """                                                            
    Decodes JSON that includes serialized ``Message`` instances.   
    """                                                            

    def process_messages(self, obj):                               
        if isinstance(obj, list) and obj:                          
            if obj[0] == MessageEncoder.message_key:               
                if obj[1]:                                         
                    print obj                                      
                    print 'OBJECT 3: {0}'.format(obj[3])           
                    obj[3] = mark_safe(obj[3])                     
                return Message(*obj[2:])                           
            return [self.process_messages(item) for item in obj]   
        if isinstance(obj, dict):                                  
            return dict([(key, self.process_messages(value))       
                         for key, value in six.iteritems(obj)])    
        return obj                                                 

    def decode(self, s, **kwargs):                                 
        decoded = super(MessageDecoder, self).decode(s, **kwargs)  
        return self.process_messages(decoded)                      

Answer 1

该错误是由“messages”cookie 格式的更改引起的，导致 Django 1.6 无法反序列化 Django 1.4 消息 cookie。

Django 1.5 包含一个修复程序，使其支持两种格式，但此修复程序尚未出现在 Django 1.6 中。

我已报告 issue为此。

同时，您可以使用以下中间件来删除旧格式的 cookie:

from django.contrib.messages.storage.cookie import CookieStorage
class FixMessageMiddleware(object):
    """
        The message cookie format has changed from Django 1.4 to
        Django 1.5. Django 1.5 probably supported both formats,
        but if you move from 1.4.x to 1.6.x directly, you will run into
        an IndexError:

        Exception Type: IndexError
        Exception Value:
        list index out of range
        Exception Location: (...) django/contrib/messages/storage/cookie.py in process_messages, line 37

        This small piece of middleware will track those cookies and destroy
        them (leaving new-style in tact)

        https://code.djangoproject.com/ticket/22426

        DISCLAIMER:
        This middleware will not attempt to rewrite the messages! You may
        miss important notifications because of this!
    """
    def process_request(self, request):
        data = request.COOKIES.get("messages")
        storage = CookieStorage(request)
        try:
            storage._decode(data)
        except IndexError:
            del request.COOKIES['messages']

我也 blogged关于这个问题(这就是上面的中间件的来源)