python - 在 Model.get_by_id() 上出现 "Expected string, got None"错误

Question

运行此代码时，使用相同的 site_id:

int_id= int(self.request.get("site_id"))
site_draft = SiteDraft.get_by_id(int_id)

我收到这个错误:

INFO     2016-06-27 12:39:19,040 module.py:788] minisites: "GET /edit/5891733057437696 HTTP/1.1" 500 -
    return self.handle_exception(e, self.app.debug)
  File "C:\Program Files\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\lib\webapp2-2.3\webapp2.py", line 545, in dispatch
    return method(*args, **kwargs)
  File "C:\Users\Yuri\Documents\WiseStamp\Server\minisites\web\pages\edit_site.py", line 21, in get
    self.post(args)
  File "C:\Users\Yuri\Documents\WiseStamp\Server\minisites\web\pages\edit_site.py", line 44, in post
    site_draft = SiteDraft.get_by_id(int_id)
  File "C:\Program Files\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\google\appengine\ext\ndb\utils.py", line 160, in positional_wrapper
    return wrapped(*args, **kwds)
  File "C:\Program Files\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\google\appengine\ext\ndb\model.py", line 3602, in _get_by_id
    return cls._get_by_id_async(id, parent=parent, **ctx_options).get_result()
  File "C:\Program Files\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\google\appengine\ext\ndb\tasklets.py", line 378, in get_result
    self.check_success()
  File "C:\Program Files\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\google\appengine\ext\ndb\tasklets.py", line 425, in _help_tasklet_along
    value = gen.send(val)
  File "C:\Program Files\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\google\appengine\ext\ndb\context.py", line 765, in get
    pbs = entity._to_pb(set_key=False).SerializePartialToString()
  File "C:\Program Files\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\google\appengine\ext\ndb\model.py", line 3167, in _to_pb
    prop._serialize(self, pb, projection=self._projection)
  File "C:\Program Files\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\google\appengine\ext\ndb\model.py", line 1422, in _serialize
    values = self._get_base_value_unwrapped_as_list(entity)
  File "C:\Program Files\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\google\appengine\ext\ndb\model.py", line 1192, in _get_base_value_unwrapped_as_list
    wrapped = self._get_base_value(entity)
  File "C:\Program Files\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\google\appengine\ext\ndb\model.py", line 1180, in _get_base_value
    return self._apply_to_values(entity, self._opt_call_to_base_type)
  File "C:\Program Files\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\google\appengine\ext\ndb\model.py", line 1352, in _apply_to_values
    value[:] = map(function, value)
  File "C:\Program Files\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\google\appengine\ext\ndb\model.py", line 1234, in _opt_call_to_base_type
    value = _BaseValue(self._call_to_base_type(value))
  File "C:\Program Files\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\google\appengine\ext\ndb\model.py", line 1255, in _call_to_base_type
    return call(value)
  File "C:\Program Files\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\google\appengine\ext\ndb\model.py", line 1331, in call
    newvalue = method(self, value)
  File "C:\Program Files\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\google\appengine\ext\ndb\model.py", line 1781, in _validate
    (value,))
BadValueError: Expected string, got None

它曾经在一天前工作，但现在只有 20% 的时间工作(这也很奇怪 - 它似乎有时工作)。更奇怪的是，我提供了一个 int 作为 site_id，但它告诉我它得到了一个 None。

请指教。

Answer 1

根据要求

详细查看堆栈跟踪并注意执行的操作，

我们看到了

 _get_by_id
 get_result
 _help_tasklet_al
 get
 _to_pb
 _serialize
 _get_base_value
_get_base_value
_apply_to_values
_opt_call_to_base
_call_to_base_type
call
_validate


BadValueError: Expected string, got None

我们看到执行路径在 _get_by_id 里面，它正在处理 get_result。因此已检索到一个实体。进一步往下看，我们看到代码实际上正在验证检索到的值，但在 _validate 调用中失败并返回 BadValueError: Expected string, got None

一个人如何在现有实体中获得错误的值(value)。通常，这是由于更改模型而造成的，您要么

• 添加了一个新的必需属性并且不更新现有实体。
• 更改了现有属性的类型
• 向属性添加验证器，但不使现有实体合规。

当您更改模型时，考虑实体迁移很重要。

干杯

T