python - ProtocolBuffers 解码错误 : truncated when using ndb. key

Question

我有这段代码，它在升级 GAE Python NDB 之前可以工作:

class MyHandler(webapp2.RequestHandler):
  def get(self,urlString):
    resume = ndb.Key(urlsafe=urlString).get()

现在，我遇到了这个错误:

Traceback (most recent call last):
  File "C:\Program Files (x86)\Google\google_appengine\lib\webapp2-2.5.2\webapp2.py", line 1535, in __call__
    rv = self.handle_exception(request, response, e)
  File "C:\Program Files (x86)\Google\google_appengine\lib\webapp2-2.5.2\webapp2.py", line 1529, in __call__
    rv = self.router.dispatch(request, response)
  File "C:\Program Files (x86)\Google\google_appengine\lib\webapp2-2.5.2\webapp2.py", line 1278, in default_dispatcher
    return route.handler_adapter(request, response)
  File "C:\Program Files (x86)\Google\google_appengine\lib\webapp2-2.5.2\webapp2.py", line 1102, in __call__
    return handler.dispatch()
  File "C:\Program Files (x86)\Google\google_appengine\lib\webapp2-2.5.2\webapp2.py", line 572, in dispatch
    return self.handle_exception(e, self.app.debug)
  File "C:\Program Files (x86)\Google\google_appengine\lib\webapp2-2.5.2\webapp2.py", line 570, in dispatch
    return method(*args, **kwargs)
  File "C:\xampp\htdocs\mapjobs\main.py", line 127, in get
    resume_key = ndb.Key(urlsafe=urlString)
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\ext\ndb\key.py", line 212, in __new__
    self.__reference = _ConstructReference(cls, **kwargs)
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\ext\ndb\utils.py", line 136, in positional_wrapper
    return wrapped(*args, **kwds)
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\ext\ndb\key.py", line 642, in _ConstructReference
    reference = _ReferenceFromSerialized(serialized)
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\ext\ndb\key.py", line 774, in _ReferenceFromSerialized
    return entity_pb.Reference(serialized)
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\datastore\entity_pb.py", line 1791, in __init__
    if contents is not None: self.MergeFromString(contents)
  File "C:\Program Files (x86)\Google\google_appengine\google\net\proto\ProtocolBuffer.py", line 84, in MergeFromString
    self.MergePartialFromString(s)
  File "C:\Program Files (x86)\Google\google_appengine\google\net\proto\ProtocolBuffer.py", line 98, in MergePartialFromString
    self.TryMerge(d)
  File "C:\Program Files (x86)\Google\google_appengine\google\appengine\datastore\entity_pb.py", line 1920, in TryMerge
    d.skipData(tt)
  File "C:\Program Files (x86)\Google\google_appengine\google\net\proto\ProtocolBuffer.py", line 524, in skipData
    self.skip(4)
  File "C:\Program Files (x86)\Google\google_appengine\google\net\proto\ProtocolBuffer.py", line 499, in skip
    if self.idx + n > self.limit: raise ProtocolBufferDecodeError, "truncated"
ProtocolBufferDecodeError: truncated

亮点可能是:

File "C:\Program Files (x86)\Google\google_appengine\lib\webapp2-2.5.2\webapp2.py", line 570, in dispatch
  return method(*args, **kwargs)
File "C:\xampp\htdocs\mapjobs\main.py", line 127, in get
  resume_key = ndb.Key(urlsafe=urlString)

出了什么问题？

Answer 1

我的猜测是，您通过 Url 参数接收作为 url 安全字符串的 key ，由于浏览器中的最大 Url 长度限制，该参数会被截断。实际上，浏览器将 URL 长度限制为最大 2000 个字符。看这个问题:What is the maximum length of a URL in different browsers?

如果您的 key 包含(多个)父 key ，则可能会超过 2000 个字符。是这样吗？请在创建和接收时检查 urlsafe 编码 key 的长度。

如果是这种情况，那么解决方法是仅使用实体(或父键的情况下的实体)的 ID 并手动构造键。