Django - 回滾保存與交易原子

Question

我想創建一個視圖，我保存一個對象，但我想撤消，如果引發一些異常保存。這是我試過的：

class MyView(View): 

    @transation.atomic 
    def post(self, request, *args, **kwargs): 
     try: 
      some_object = SomeModel(...) 
      some_object.save() 

      if something: 
       raise exception.NotAcceptable() 
       # When the workflow comes into this condition, I think the previous save should be undome 
       # Whant am I missing? 

     except exception.NotAcceptable, e: 
      # do something 

我在做什麼錯？即使在引發異常時some_object仍然在DataBase中。

Answer 1

Atomicity Documentation

總之，@transaction.atomic將在數據庫上執行事務，如果您的視圖產生沒有錯誤的響應。因爲你自己捕捉異常，所以Django顯示你的視圖執行得很好。

如果趕上例外，你需要自己處理：Controlling Transactions

如果你需要產生故障的情況下適當的JSON響應：

from django.db import SomeError, transaction 

def viewfunc(request): 
    do_something() 

    try: 
     with transaction.atomic(): 
      thing_that_might_fail() 
    except SomeError: 
     handle_exception() 

    render_response() 

Answer 2

但是，如果一個例外飾有transaction.atomic功能情況，那麼你不要有什麼關係，它會rollback automatically to the savepoint created by the decorator before running the your function，爲documented：

原子允許我們創建一個塊在其中保證數據庫的原子性的代碼。如果代碼塊成功完成，則更改將提交給數據庫。如果有異常，則更改將回滾。

如果異常是在釣到除塊，那麼就應該再上調原子捕獲它，做回退，即：

try: 
     some_object = SomeModel(...) 
     some_object.save() 

     if something: 
      raise exception.NotAcceptable() 
      # When the workflow comes into this condition, I think the previous save should be undome 
      # Whant am I missing? 

    except exception.NotAcceptable, e: 
     # do something 
     raise # re-raise the exception to make transaction.atomic rollback 

另外，如果你想要更多的控制，您可以手動回滾到previously set savepoint，即：

class MyView(View): 
    def post(self, request, *args, **kwargs): 
     sid = transaction.savepoint() 
     some_object = SomeModel(...) 
     some_object.save() 

     if something: 
      transaction.savepoint_rollback(sid) 
     else: 
      try: 
       # In worst case scenario, this might fail too 
       transaction.savepoint_commit(sid) 
      except IntegrityError: 
       transaction.savepoint_rollback(sid)