Question

以下代码

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

会产生以下错误：

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

如何规避这一限制？

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 )

Answer 2

提供不同的集合名称

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

默认情况下，每个db.ReferenceProperty都会在引用的模型中创建一个名为referencedmodelname_set的集合。

例如：

class OwnedCar(db.Model):
   brand  =  db.StringProperty(required=True)
   owner  =  db.ReferenceProperty(Human, required=True)

class Human(db.Model):
    name    = db.StringProperty(required=True)
    drives  = db.ReferenceProperty(reference_class=Car)

默认情况下，每个人都有一个名为ownedcar_set的属性。如果您两次引用同一个模型，则会创建collection_name冲突。因此，您应该添加collection_name来区分集合。

更多参考此处

Answer 3

为它们提供不同的集合名称：

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

友情链接