在shebang路径(path in shebang)

 第一 
 
 正如文档所述 
 
 
 
 原子性是数据库事务的定义属性。 atomic允许我们创建一个代码块，在该代码块中保证数据库的原子性。 如果代码块成功完成，则更改将提交到数据库。 如果存在异常，则回滚更改。 
 
 
 在您的示例中，如果emit_event正在执行某些操作，则需要使用atomic ，并且只有在所有emit_event函数调用和queryset.update成功完成时才需要执行此更新。 但是如果emit_event状态不会影响你的业务更新逻辑，那么atomic就是多余的，因为正如你所说的那样， update具有内部atomic 。 
 
 第二 
 
 查询集很懒惰。 这意味着当您迭代查询集时，将对其进行评估。 所以你需要做这样的事情。 回答最新评论 
 
try:
    queryset = Model.objects.filter(a=1)
    item_ids = list(queryset.values_list('id', flat=True)) # store ids for later
    if item_ids: # optimzing here instead of queryset.count() so there won't be hit to DB
        with transaction.atomic():
            queryset.update(a=2) # queryset will [] after this.
            for item in Model.objects.filter(id__in=item_ids):  # <- new queryset which gets only updated objects
                item.emit_event('Updated')
except:
    logger.info('Exception')
 
 看到我们在迭代它时获取新的查询集以获取更新的项目 

First
 
As docs state
 
 
 
Atomicity is the defining property of database transactions. atomic allows us to create a block of code within which the atomicity on the database is guaranteed. If the block of code is successfully completed, the changes are committed to the database. If there is an exception, the changes are rolled back.
 
 
In your example you would need atomic if emit_event is doing something and you want this update to be done only if all emit_event function calls and queryset.update are successfull. But if states of emit_event does not affect your business logic of update, atomic here would be redundant because as you said yourself update has internal atomic.
 
Second
 
Querysets are lazy. Which means evaluation of queryset will be done when you are iterating over it. So you need to do something like this. Answering latest comment
 
try:
    queryset = Model.objects.filter(a=1)
    item_ids = list(queryset.values_list('id', flat=True)) # store ids for later
    if item_ids: # optimzing here instead of queryset.count() so there won't be hit to DB
        with transaction.atomic():
            queryset.update(a=2) # queryset will [] after this.
            for item in Model.objects.filter(id__in=item_ids):  # <- new queryset which gets only updated objects
                item.emit_event('Updated')
except:
    logger.info('Exception')
 
See there we make new queryset when iterating over it to get updated items