问题描述
在我的Django应用程序中，我经常需要做类似于 get_or_create（）的事情。例如
In my Django app very often I need to do something similar to get_or_create(). E.g.,
$ c> get_or_create（）看起来不是线程安全的。线程A检查和查找记录X不存在。然后线程B检查并发现记录X不存在。现在线程A和线程B都将创建一个新的记录X.
But looking into the doc for get_or_create() it looks like it's not threadsafe. Thread A checks and finds Record X does not exist. Then Thread B checks and finds that Record X does not exist. Now both Thread A and Thread B will create a new Record X.
这是一个很常见的情况。如何以线程安全的方式处理它？
This must be a very common situation. How do I handle it in a threadsafe way?
推荐答案
是的。
SQL中的标准解决方案是简单地尝试创建记录。如果它工作，这是好的。继续。
The "standard" solution in SQL is to simply attempt to create the record. If it works, that's good. Keep going.
如果尝试创建记录从RDBMS获取重复异常，则执行SELECT并继续。
If an attempt to create a record gets a "duplicate" exception from the RDBMS, then do a SELECT and keep going.
然而，Django有一个ORM层，它有自己的缓存。所以逻辑被反转，使常见的情况下直接和快速工作，而不常见的情况（副本）引发罕见的异常。
Django, however, has an ORM layer, with it's own cache. So the logic is inverted to make the common case work directly and quickly and the uncommon case (the duplicate) raise a rare exception.
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