Question

I’m playing with the project appengine-rest-server to create the REST webservices for all the existing models. I got a strange error, the first time I query the browser: http://localhost:8080/rest/metadata/user, it gives me the result:

      <xs:schema>
      −
      <xs:element name="user">
      −
      <xs:complexType>
      −
      <xs:sequence>
      <xs:element maxOccurs="1" minOccurs="0" name="key" type="xs:normalizedString"/>
      <xs:element maxOccurs="1" minOccurs="0" name="surname" type="xs:string"/>
      <xs:element maxOccurs="1" minOccurs="0" name="firstname" type="xs:string"/>
      <xs:element maxOccurs="1" minOccurs="0" name="ages" type="xs:long"/>
      <xs:element maxOccurs="1" minOccurs="0" name="sex" type="xs:boolean"/>
      <xs:element maxOccurs="1" minOccurs="0" name="updatedDate" type="xs:dateTime"/>
      <xs:element maxOccurs="1" minOccurs="0" name="createdDate" type="xs:dateTime"/>
      </xs:sequence>
      </xs:complexType>
      </xs:element>
      </xs:schema>

But refreshing the page, gives me this error:

  Traceback (most recent call last):
    File "/Users/foo/Documents/AppEngine/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 3185, in _HandleRequest
      self._Dispatch(dispatcher, self.rfile, outfile, env_dict)
    File "/Users/foo/Documents/AppEngine/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 3128, in _Dispatch
      base_env_dict=env_dict)
    File "/Users/foo/Documents/AppEngine/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 515, in Dispatch
      base_env_dict=base_env_dict)
    File "/Users/foo/Documents/AppEngine/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 2387, in Dispatch
      self._module_dict)
    File "/Users/foo/Documents/AppEngine/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 2297, in ExecuteCGI
      reset_modules = exec_script(handler_path, cgi_path, hook)
    File "/Users/foo/Documents/AppEngine/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/dev_appserver.py", line 2195, in ExecuteOrImportScript
      script_module.main()
    File "/Users/foo/Documents/AppEngine/helloworld/main.py", line 48, in main
      rest.Dispatcher.add_models({"user": UserModel})
    File "/Users/foo/Documents/AppEngine/helloworld/rest/__init__.py", line 845, in add_models
      cls.add_model(model_name, model_type)
    File "/Users/foo/Documents/AppEngine/helloworld/rest/__init__.py", line 863, in add_model
      raise KeyError("name %s already used" % model_name)
  KeyError: 'name user already used'

Can someone give me the explanation on why it happens? Restarting the server, run on the browser again I get the xml result, but refreshing causes the error. Is it a bug in the appengine-rest-server application or it is in my code? My helloworld application is available for download here.

Answer 1

Since you have a main() function, the App Engine caches your module and imports. Hence within the same runtime, you may call add_models() more than once. If you move the rest initialization code to module level (or into a function that gets called once during module initialization, not during every call to main()) it should work.