Django:如何锁定行以供阅读？

Question

我的表包含并发工作人员的“任务”。所以工作人员应该能够从表中“获取”任务，这意味着自动检查任务是否存在，如果存在，则将其删除。其他工作人员应该被锁定，直到这个原子过程完成。如何在 Django 中执行这样的锁定？

我正在使用如下代码，但行未锁定读取，两个并发工作人员都进入事务，找到相同的任务，一个成功获得它，但第二个得到 OperationalError('database is locked',)

使用SQLite

class Task(models.Model):

    @staticmethod
    def get():
        with transaction.atomic():
            task = Task.objects.select_for_update().filter(...).first()
            if task:
                task.delete()
                return task

        return None

Answer 1

SQLite 不支持行级锁，部分原因是它是基于文件的数据库:

https://www.sqlite.org/atomiccommit.html

The first step toward reading from the database file is obtaining a shared lock on the database file. A "shared" lock allows two or more database connections to read from the database file at the same time. But a shared lock prevents another database connection from writing to the database file while we are reading it.

最好的办法是切换到生产质量数据库，例如 PostgreSQL :

13.3.2. Row-level Locks

In addition to table-level locks, there are row-level locks, which are listed as below with the contexts in which they are used automatically by PostgreSQL.