覆盖使用django-mptt的模型的save（）方法

Question

我一直在我的项目中使用django-mptt一段时间，这很棒。最近，我发现需要重写使用MPTT模型的save（）方法，当我尝试保存模型的新实例，我得到一个错误：

Exception Type: ValueError at /admin/scrivener/page/add/ 
Exception Value: Cannot use None as a query value 

我假设这是事实的结果，即实例还没有陷入树中，但我不知道如何去解决这个问题。我在这个项目的追踪器上添加了一个关于它的评论，但我希望这里的某个人能够让我更快地走上正确的轨道。

这是回溯。

Environment: 

Request Method: POST 
Request URL: http://localhost:8000/admin/scrivener/page/add/ 
Django Version: 1.2 rc 1 SVN-13117 
Python Version: 2.6.4 
Installed Applications: 
['django.contrib.auth', 
'django.contrib.contenttypes', 
'django.contrib.sessions', 
'django.contrib.sites', 
'django.contrib.admin', 
'django.contrib.sitemaps', 
'mptt', 
'filebrowser', 
'south', 
'haystack', 
'django_static', 
'etc', 
'scrivener', 
'gregor', 
'annunciator'] 
Installed Middleware: 
('django.middleware.common.CommonMiddleware', 
'django.contrib.sessions.middleware.SessionMiddleware', 
'django.contrib.auth.middleware.AuthenticationMiddleware') 


Traceback: 
File "B:\django-apps\3rd Party Source\django\core\handlers\base.py" in get_response 
    100.      response = callback(request, *callback_args, **callback_kwargs) 
File "B:\django-apps\3rd Party Source\django\contrib\admin\options.py" in wrapper 
    239.     return self.admin_site.admin_view(view)(*args, **kwargs) 
File "B:\django-apps\3rd Party Source\django\utils\decorators.py" in _wrapped_view 
    74.      response = view_func(request, *args, **kwargs) 
File "B:\django-apps\3rd Party Source\django\views\decorators\cache.py" in _wrapped_view_func 
    69.   response = view_func(request, *args, **kwargs) 
File "B:\django-apps\3rd Party Source\django\contrib\admin\sites.py" in inner 
    190.    return view(request, *args, **kwargs) 
File "B:\django-apps\3rd Party Source\django\utils\decorators.py" in _wrapper 
    21.    return decorator(bound_func)(*args, **kwargs) 
File "B:\django-apps\3rd Party Source\django\utils\decorators.py" in _wrapped_view 
    74.      response = view_func(request, *args, **kwargs) 
File "B:\django-apps\3rd Party Source\django\utils\decorators.py" in bound_func 
    17.     return func(self, *args2, **kwargs2) 
File "B:\django-apps\3rd Party Source\django\db\transaction.py" in _commit_on_success 
    299.      res = func(*args, **kw) 
File "B:\django-apps\3rd Party Source\django\contrib\admin\options.py" in add_view 
    795.     self.save_model(request, new_object, form, change=False) 
File "B:\django-apps\3rd Party Source\django\contrib\admin\options.py" in save_model 
    597.   obj.save() 
File "B:\django-apps\scrivener\models.py" in save 
    205.  self.url = self.get_absolute_url() 
File "B:\django-apps\3rd Party Source\django\utils\functional.py" in _curried 
    55.   return _curried_func(*(args+moreargs), **dict(kwargs, **morekwargs)) 
File "B:\django-apps\3rd Party Source\django\db\models\base.py" in get_absolute_url 
    940.  return settings.ABSOLUTE_URL_OVERRIDES.get('%s.%s' % (opts.app_label, opts.module_name), func)(self, *args, **kwargs) 
File "B:\django-apps\3rd Party Source\django\db\models\__init__.py" in inner 
    31.   bits = func(*args, **kwargs) 
File "B:\django-apps\scrivener\models.py" in get_absolute_url 
    194.  for ancestor in self.get_ancestors(): 
File "B:\django-apps\3rd Party Source\mptt\models.py" in get_ancestors 
    23.   opts.tree_id_attr: getattr(self, opts.tree_id_attr), 
File "B:\django-apps\3rd Party Source\django\db\models\manager.py" in filter 
    141.   return self.get_query_set().filter(*args, **kwargs) 
File "B:\django-apps\3rd Party Source\django\db\models\query.py" in filter 
    550.   return self._filter_or_exclude(False, *args, **kwargs) 
File "B:\django-apps\3rd Party Source\django\db\models\query.py" in _filter_or_exclude 
    568.    clone.query.add_q(Q(*args, **kwargs)) 
File "B:\django-apps\3rd Party Source\django\db\models\sql\query.py" in add_q 
    1131.        can_reuse=used_aliases) 
File "B:\django-apps\3rd Party Source\django\db\models\sql\query.py" in add_filter 
    1000.     raise ValueError("Cannot use None as a query value") 

Exception Type: ValueError at /admin/scrivener/page/add/ 
Exception Value: Cannot use None as a query value 

Answer 1

解决了这个问题，添加了一个我自定义的保存方法。假如将其从

def save(self, *args, **kwargs): 
    self.url = self.get_absolute_url() 
    super(Page, self).save(*args, **kwargs) 

更改此设置：

def save(self, *args, **kwargs): 
    if not self.id: 
     Page.tree.insert_node(self, self.parent) 
    self.url = self.get_absolute_url() 
    super(Page, self).save(*args, **kwargs) 

Answer 2

改变也应该工作的顺序，因为对象应在保存和save() - 方法”不是个返回任何东西得到一个ID！

def save(self, *args, **kwargs): 
    super(Page, self).save(*args, **kwargs)  
    self.url = self.get_absolute_url()