Django：如何做get_or_create（）以线程安全的方式？ [英] Django: how to do get_or_create() in a threadsafe way?

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.,

用户提交标签。需要看看是否
该标签已经在数据库中。
如果没有，为它创建一个新记录。如果
，它只是更新现有的
记录。

User submits a tag. Need to see if that tag already is in the database. If not, create a new record for it. If it is, just update the existing record.

$ 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

这必须是很常见的情况。如何以线程安全的方式处理它？<​​/ p>

This must be a very common situation. How do I handle it in a threadsafe way?

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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