为什么这个会失败？（谷歌App Engine数据存储，Python）

Question

  1 from google.appengine.ext import webapp
  2 from google.appengine.ext.webapp.util import run_wsgi_app
  3 from google.appengine.ext import db
  4 
  5 a = db.GqlQuery('SELECT * FROM Store WHERE count = True').count
  6 
  7 print 'Content-Type: text/plain'
  8 print ''
  9 print str(a)+'blah blah'

表格 'Store' 是存在的。

错误是：

Traceback (most recent call last):
  File "/opt/google-appengine/google/appengine/tools/dev_appserver.py", line 3245, in _HandleRequest
    self._Dispatch(dispatcher, self.rfile, outfile, env_dict)
  File "/opt/google-appengine/google/appengine/tools/dev_appserver.py", line 3186, in _Dispatch
    base_env_dict=env_dict)
  File "/opt/google-appengine/google/appengine/tools/dev_appserver.py", line 531, in Dispatch
    base_env_dict=base_env_dict)
  File "/opt/google-appengine/google/appengine/tools/dev_appserver.py", line 2410, in Dispatch
    self._module_dict)
  File "/opt/google-appengine/google/appengine/tools/dev_appserver.py", line 2320, in ExecuteCGI
    reset_modules = exec_script(handler_path, cgi_path, hook)
  File "/opt/google-appengine/google/appengine/tools/dev_appserver.py", line 2216, in ExecuteOrImportScript
    exec module_code in script_module.__dict__
  File "/home/jck/bitsconv/bitsconv.py", line 5, in <module>
    a = db.GqlQuery('SELECT * FROM Store WHERE count = True').count()
  File "/opt/google-appengine/google/appengine/ext/db/__init__.py", line 2298, in __init__
    model_class = class_for_kind(self._proto_query._entity)
  File "/opt/google-appengine/google/appengine/ext/db/__init__.py", line 266, in class_for_kind
    raise KindError('No implementation for kind \'%s\'' % kind)
KindError: No implementation for kind 'Store'

Answer 1

你需要为“商店”定义一个模型。即使你已经成功把数据存入数据库作为商店的记录，如果没有这个模型类，程序还是会出错。

我通过把一个正常工作的应用中的模型类重命名来验证这一点，那个应用里已经存有这种类型的数据。结果也抛出了同样的错误，所以我猜这也是你遇到问题的原因。把下面这段代码加到你的应用中，看看错误是否有所改变：

class Store(db.Model):
    pass

另外，这个错误不是由这个引起的，但count其实是一个方法。你应该使用下面的代码：

a = db.GqlQuery('SELECT * FROM Store WHERE count = True').count()