选择更新查询：锁定等待超时超出错误

为了避免竞争条件，我需要在查询数据库时使用 select for update 功能，以便锁定行直到事务结束。由于Django 1.3中不存在select_for_update查询，所以我通过使用一个通过执行一个原始sql查询返回查询集的类方法来完成一个解决方法。

To avoid race conditions, I need to use select for update functionality while querying database so that it locks the row until the end of the transaction. Since select_for_update query is not present in Django 1.3, I have done a workaround it by using a class method which returns query sets by doing a raw sql query.

#models.py
class AccountDetails(models.Model):
    user = models.OneToOneField(User)
    amount = models.IntegerField(max_length=15,null=True,blank=True)

    @classmethod
    def get_locked_for_update(cls,userid):
        accounts = cls.objects.raw("SELECT * FROM b2b_accountdetails WHERE user_id ="+str(userid)+" FOR UPDATE")
        return accounts[0]

如何在视图中使用。

account = AccountDetails.get_locked_for_update(userid)
account.amount = account.amount - fare
account.save()

在最后一行我收到此错误：
OperationalError：（1205，超过锁定等待超时;尝试重新启动事务）

On the last line I'm getting this error: OperationalError: (1205, 'Lock wait timeout exceeded; try restarting transaction')

I n dbshel​​l，运行 save（）行：

In dbshell, after running the save() line:

mysql> SHOW FULL PROCESSLIST;
+-----+------+-----------+-----------+---------+------+----------+-----------------------------------------------------------------------------------------------------+
| Id  | User | Host      | db     | Command | Time | State    | Info                                                                                                |
+-----+------+-----------+-----------+---------+------+----------+--------------------------    ---------------------------------------------------------------------------+
|  51 | root | localhost | dbname | Query   |    0 | NULL     | SHOW FULL PROCESSLIST                                                                               |
| 767 | root | localhost | dbname | Sleep   |   59 |          | NULL                                                                                                |
| 768 | root | localhost | dbname | Query   |   49 | Updating | UPDATE `b2b_accountdetails` SET `user_id` = 1, `amount` = 68906 WHERE `appname_accountdetails`.`id` = 1 |
+-----+------+-----------+-----------+---------+------+----------+--------------------------    ---------------------------------------------------------------------------+

根据我的理解，应该在第一个数据更改查询（如更新，删除等）上发布锁。

According to my understanding the lock should be released on the first data-altering query like update, delete etc.

但是， save（） / code>语句被阻止并保持等待。任何想法为什么会发生这种情况？当我打电话 account.save（）时，我认为是没有选择由更新查询选择开始的上一个事务。

But the save() statement is getting blocked and is kept on wait. Any idea why this is happening? What I think is when I'm calling account.save() it's not picking up the previous transaction started by select for update query.

我错过了一些明显的东西吗？请帮助。

Am I missing something obvious? Kindly help.