此交易方法是否有效？ [英] Will this transaction method work?

问题描述

我试图为应用引擎数据存储区编写一个事务性方法，但很难测试它是否正常工作，所以我试图首先验证我的方法。我有一个post请求，检查一个属性是否为true，如果不是true，则执行其他操作并将其设置为true。

I'm trying to write a transactional method for the app engine datastore but it's hard to test if it's working so I'm trying to validate my approach first. I have a post request that checks if a property is true, and if not true then do something else and set it to true.

def post(self):
    key = self.request.get('key')
    obj = db.get(key)
    if obj.property is False:
        update_obj(ojb.key()) // transactional method to update obj and set value to True

    if obj.property is True:
        // do something else

推荐答案

def post(self):
    key = self.request.get('key')
    # this gets the most recent entity using the key
    obj = db.get(key)
    if not obj.property:
        # You should do the most recent check inside the transaction. 
        # After the above if-check the property might have changed by 
        # a faster request.
        update_obj(ojb.key()) # transactional method to update obj and set value to True

    if obj.property:
       # do something else

将交易视为一组实体上的所有执行或全部失败的操作。

Consider transactions as a group of actions on an entity that will all execute or all fail.

交易确保其内的任何内容都将保持一致。如果某件事情改变了一个实体，并且变得与以前不同，交易将会失败，然后再次重复。

Transactions ensure that anything inside them will remain consistent. If something alters an entity and becomes different than it was, the transaction will fail and then repeat again.

如果我理解您需要的是另一种方法：

Another approach if I understand what you need:

def post(self):
    key = self.request.get('key')
    self.check_obj_property(key)
    # continue your logic

@db.transctional
def check_obj_property(key):
    obj = db.get(key)
    if obj.property:
        #it's set already continue with other logic
        return
    # Its not set so set it and increase once the counter. 
    obj.property = True
    # Do something else also?
    obj.count += 1
    # Save of course
    obj.put()

正如您所看到的，我已将所有支票放入交易中。
上面的代码，如果同时运行，只会增加一次一次。
假设它像一个计数器，它计数 obj.property 已被设置为 True

As you see I've put all my checks inside a transaction. The above code, if run concurrently, will only increase the count once. Imagine it like a counter that counts how many times the obj.property has been set to True

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