如何在Sqlalchemy orm会话中正确禁用缓存？ [英] How to disable caching correctly in Sqlalchemy orm session?

问题描述

我让我线程进入守护程序，该线程循环并执行以下查询：

I have I thread in a daemon, that loops and performs the following query:

    try:
        newsletter = self.session.query(models.Newsletter).\
               filter(models.Newsletter.status == 'PROCESSING').\
               limit(1).one()
    except sa.orm.exc.NoResultFound:
        self.logger.debug('No PROCESSING newsletters found. Sleeping...')
        self.sleep()
        return
    # (...) more code to do with found newsletter

其中sleep方法只是停止执行该线程在配置的时间内运行，并且return语句返回到主循环。但是我发现，如果在守护程序运行时将任何新闻通讯的状态更改为处理中，则什么也不会发生。查询仍然引发NoResultFound。但是，如果重新启动守护程序，它将找到新闻通讯。因此，我知道该查询的结果必须缓存。我该怎么做才能使缓存无效？ session.expire_all（）不起作用。我还可以在每次迭代时创建新的Session（）对象，但不知道这是否是一种有关系统资源的好方法。

Where the sleep method just stops the execution of this thread for the configured time and the return statement returns to the main loop. However I found, that if I change any newsletter's status to 'PROCESSING' while the daemon is running, nothing happens, ie. the query still raises NoResultFound. If I restart the daemon however, it will find the newsletter. So I see, that the results of this query must be cached. What can I do to invalidate the cache? session.expire_all() doesn't work. I could also create new Session() object every iteration, but don't know if it's a good approach regarding system resources.

推荐答案

SQLAlchemy 不会自行缓存。除非您明确实现了缓存，否则就是这样。

SQLAlchemy doesn't cache on itself. Unless you explicitly implemented a cache, like this one.

通过 echo = True 到您的 sessionmaker 并查看 日志记录输出。

Pass echo=True to your sessionmaker and look into the logging output.

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