Question

The following code

class Translation(db.Model):
    origin = db.ReferenceProperty(Expression, required=True)
    target = db.ReferenceProperty(Expression, required=True)

produces the following error:

Traceback (most recent call last):
File “C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\dev_appserver.py”, line 4053, in _HandleRequest
self._Dispatch(dispatcher, self.rfile, outfile, env_dict)
File “C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\dev_appserver.py”, line 3977, in _Dispatch
base_env_dict=env_dict)
File “C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\dev_appserver.py”, line 588, in Dispatch
base_env_dict=base_env_dict)
File “C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\dev_appserver.py”, line 3050, in Dispatch
self._module_dict)
File “C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\dev_appserver.py”, line 2954, in ExecuteCGI
reset_modules = exec_script(handler_path, cgi_path, hook)
File “C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\dev_appserver.py”, line 2834, in ExecuteOrImportScript
exec module_code in script_module.dict
File “D:\svn\language\Web\src\controller.py”, line 5, in
from model import *
File “C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\dev_appserver.py”, line 1505, in Decorate
return func(self, *args, **kwargs)
File “C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\dev_appserver.py”, line 2450, in load_module
return self.FindAndLoadModule(submodule, fullname, search_path)
File “C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\dev_appserver.py”, line 1505, in Decorate
return func(self, *args, **kwargs)
File “C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\dev_appserver.py”, line 2339, in FindAndLoadModule
description)
File “C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\dev_appserver.py”, line 1505, in Decorate
return func(self, *args, **kwargs)
File “C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\dev_appserver.py”, line 2282, in LoadModuleRestricted
description)
File “D:\svn\language\Web\src\model.py”, line 24, in
class Translation(db.Model):
File “C:\Program Files (x86)\Google\google_appengine\google\appengine\ext\db__init__.py”, line 500, in init
_initialize_properties(cls, name, bases, dct)
File “C:\Program Files (x86)\Google\google_appengine\google\appengine\ext\db__init__.py”, line 415, in _initialize_properties
attr.property_config(model_class, attr_name)
File “C:\Program Files (x86)\Google\google_appengine\google\appengine\ext\db__init__.py”, line 3461, in property_config
self.collection_name))
DuplicatePropertyError: Class Expression already has property translation_set

How to circumvent this limitation?

Answer 1

class Translation(db.Model):
    origin = db.ReferenceProperty(Expression, required=True, collection_name='translation_origins')
    target = db.ReferenceProperty(Expression, required=True, collection_name='translation_targets')