GAE錯誤：AttributeError的： 'NoneType' 對象有沒有屬性 'user_is_member'

Question

class Thread(db.Model): 
    members = db.StringListProperty() 

    def user_is_member(self, user): 
    return str(user) in self.members 

和

thread = Thread.get(db.Key.from_path('Thread', int(id))) 
is_member = thread.user_is_member(user) 

但錯誤是：

Traceback (most recent call last): 
    File "D:\Program Files\Google\google_appengine\google\appengine\ext\webapp\__init__.py", line 511, in __call__ 
    handler.get(*groups) 
    File "D:\Program Files\Google\google_appengine\google\appengine\ext\webapp\util.py", line 62, in check_login 
    handler_method(self, *args) 
    File "D:\zjm_code\forum_blog_gae\main.py", line 222, in get 
    is_member = thread.user_is_member(user) 
AttributeError: 'NoneType' object has no attribute 'user_is_member' 

爲什麼呢？

感謝

Answer 1

你試圖通過按鍵獲取的實體，但與該鍵無實體存在，因此獲得（）將返回無。你需要檢查試圖採取行動，那麼在此之前，一個有效的實體返回，就像這樣：

thread = Thread.get(db.Key.from_path('Thread', int(id))) 
if thread: 
    is_member = thread.user_is_member(user) 
else: 
    is_member = False 

或等價：

thread = Thread.get(db.Key.from_path('Thread', int(id))) 
is_member = thread.user_is_member(user) if thread else False