Question

遇到错误

BadValueError: Virtual property is read-only

我在文档中没有找到有关此错误的任何内容。这是什么意思？这是代码的相关部分。它一直有效，直到最近的SDK更新。

date = dt.datetime.strptime(self.json['birthday'],"%Y-%m-%d").date()
if self.json.has_key('avatar'):
    img = base64.b64decode(self.json['avatar'])
else:
    img = None
    log.info('No avatar')
user = db.User(
    name=self.json['name'], 
    password=self.json['password'], 
    full_name=self.json['full_name'],
    email = self.json['email'],
    birthday = date,
    avatar = img)
user.put()

服务器日志

  File "/api/tornado/web.py", line 1064, in _execute
    getattr(self, self.request.method.lower())(*args, **kwargs)
  File "user.py", line 31, in post
    avatar = img)
  File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/ext/db/__init__.py", line 970, in __init__
    prop.__set__(self, value)
  File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/ext/db/__init__.py", line 615, in __set__
    setattr(model_instance, self._attr_name(), value)
  File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/ext/db/__init__.py", line 3874, in __set__
    raise BadValueError('Virtual property is read-only')
BadValueError: Virtual property is read-only
INFO     2013-06-08 07:44:37,776 server.py:585] default: "POST /api/user/create HTTP/1.1" 500 93

数据库模型

class User(db.Model):
    name = db.StringProperty(required=True)
    password = db.StringProperty(required=True)
    email = db.StringProperty(required=True)
    full_name = db.StringProperty()    
    birthday = db.DateProperty()
    avatar = db.BlobProperty()

如果我删除

avatar = img

然后是上面一行的错误。

Answer 1

您错过了以下文档：

Blob is for binary data, such as images. **It takes a str value**, but this value
is stored as a byte string and is not encoded as text. Use a Text instance for 
large text data.

您需要做的是通过以下教程上传blob：https://developers.google.com/appengine/docs/python/blobstore

并在您的模型中：

 avatar = db.BlobProperty() <-- you store the key to the uploaded avatar.

因此，在您的模型中，您只需将密钥存储到blob引用而不是blob本身。我希望这很清楚。

另外看看下面的教程，这个教程对我有很大的帮助：https://gist.github.com/348025/d4fc873bda4a650210559f881738cc55a667ff2a

Answer 2

该异常来自_ReverseReferenceProperty类。当您的模型指向db.ReferenceProperty时，似乎会使用此选项。您没有提供足够的详细信息，但我怀疑您有另一个使用db.ReferenceProperty的模型，并且您将collection_name设置为与User的现有属性之一相同的名称。

例如，如果您有这样的模型：

class Email(db.Model):
  user = db.ReferenceProperty(User, collection_name=email)

User.email将变为只读，当您尝试设置它时，您会看到该异常。搜索其他模型以查看是否存在db.ReferenceProperty(User, collection_name=...)。

avatar = img)上的错误略有误导。这只是多行声明的最后一行。它可能是该陈述的任何部分。

错误BadValueError：虚拟属性是只读的

2 个答案: