英文:
How do I do table locking in GORM(Golang)?
问题
在GORM（go-gorm）中如何进行表锁定？
我找到了一种进行行锁定的方法，但是找不到进行表锁定的方法。
英文:
How do I do table locking in GORM(go-gorm)?
I found a way to do row locking, but could not find a way to do table locking.
答案1
得分: 3
你可以根据gorm.io的文档使用以下代码：
行级锁模式，FOR UPDATE
db.Clauses(clause.Locking{Strength: "UPDATE"}).Find(&users)
// SELECT * FROM `users` FOR UPDATE
此外，你还可以使用其他锁模式，例如：KEY SHARE, SHARE, NO KEY UPDATE.
表级锁模式
目前我所知，Gorm没有提供直接锁定表的选项，因为在合并Clauses时，Gorm总是会添加FOR关键字。但你可以使用原始查询来实现你想要的效果：
db.Exec("LOCK TABLE table_name_here IN ACCESS EXCLUSIVE MODE")
// LOCK [ TABLE ] [ ONLY ] name [ * ] [, ...] [ IN lockmode MODE ] [ NOWAIT ]
其中lockmode可以是以下之一：
ACCESS SHARE | ROW SHARE | ROW EXCLUSIVE | SHARE UPDATE EXCLUSIVE
| SHARE | SHARE ROW EXCLUSIVE | EXCLUSIVE | ACCESS EXCLUSIVE
关于Postgres锁的更多信息，请参考这里。
添加选项
你可以使用Options来添加任何你想要的选项，这些选项将出现在Strength之后。
db.Clauses(clause.Locking{
Strength: "UPDATE",
Options: "NOWAIT",
}).Find(&users)
// SELECT * FROM `users` FOR UPDATE NOWAIT
如何解锁：
当你使用Strength: "UPDATE"时，这意味着表正在锁定（FOR UPDATE），并且在更新后将被解锁。
其他一些更新包括：
-
Strength: "SHARE"
英文:
You could use this code according to gorm.io docs:
Row-Level Lock Modes, FOR UPDATE
db.Clauses(clause.Locking{Strength: "UPDATE"}).Find(&users)
// SELECT * FROM `users` FOR UPDATE
Also, you could use other lock mode instead of UPDATE, like: KEY SHARE, SHARE, NO KEY UPDATE.
Table-Level Lock Modes
For locking a table, as far as I can see there is no option with Gorm right now, because Gorm always put FOR, when merging Clauses.
but you can use a raw query to achieve what you want:
db.Exec("LOCK TABLE table_name_here IN ACCESS EXCLUSIVE MODE")
// LOCK [ TABLE ] [ ONLY ] name [ * ] [, ...] [ IN lockmode MODE ] [ NOWAIT ]
where lockmode is one of:
ACCESS SHARE | ROW SHARE | ROW EXCLUSIVE | SHARE UPDATE EXCLUSIVE
| SHARE | SHARE ROW EXCLUSIVE | EXCLUSIVE | ACCESS EXCLUSIVE
More info on Postgres locks here
Add options
You can use Options to add any option that you want, this will be appear after the Strength.
db.Clauses(clause.Locking{
Strength: "UPDATE",
Options: "NOWAIT",
}).Find(&users)
// SELECT * FROM `users` FOR UPDATE NOWAIT
How to unlock:
When you are using Strength: "UPDATE", it means the table is Locking (FOR UPDATE) And it will be unlock after updating.
Some other updates are:
Strength: "SHARE"
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