MyBatis-Plus 实现乐观锁_mybatisplus 锁定记录

1 主要适用场景

当要更新一条记录的时候，希望这条记录无法被别人更新，也就是说实现线程安全的数据更新。

2 乐观锁实现方式

取出记录时，获取当前 version

更新时，带上这个version

执行更新时， set version = newVersion where version = oldVersion

如果 version 不对，就更新失败

3 图例

张三和李四更新同一条记录，如果不加乐观锁，谁后更新以谁的数据为准。加上乐观锁后，谁先抢到乐观锁，就以谁的更新为准，其他用户更新无效。

二 实战

1 主要流程见下图

2 数据库 

CREATE TABLE `user` (
  `id` bigint(20) NOT NULL DEFAULT '0' COMMENT '主键ID',
  `NAME` varchar(30) DEFAULT NULL COMMENT '姓名',
  `age` int(11) DEFAULT NULL COMMENT '年龄',
  `email` varchar(50) DEFAULT NULL COMMENT '邮箱',
  `create_time` datetime DEFAULT NULL,
  `update_time` datetime DEFAULT NULL,
  `version` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

 3 实体类

@Data
public class User {
    @TableId(type = IdType.ASSIGN_ID)
    private Long id;
 
    private String name;
    private Integer age;
    private String email;
 
    @TableField(fill = FieldFill.INSERT)
    private Date createTime;  // create_time
 
    @TableField(fill = FieldFill.INSERT_UPDATE)
    private Date updateTime; // update_time
 
    @Version
    @TableField(fill = FieldFill.INSERT)
    private Integer version;
}

4 配置乐观锁

@Configuration
@MapperScan("com.cakin.demomptest.mapper")
public class MpConfig {
    /**
     * 乐观锁插件
     */
    @Bean
    public OptimisticLockerInterceptor optimisticLockerInterceptor() {
        return new OptimisticLockerInterceptor();
    }
}

5 插入时，让版本的默认值为1

// mp执行添加操作，这个方法执行
@Override
public void insertFill(MetaObject metaObject) {
    this.setFieldValByName("createTime",new Date(),metaObject);
    this.setFieldValByName("updateTime",new Date(),metaObject);
    this.setFieldValByName("version",1,metaObject);
}

6 测试

先添加一条数据

// 添加一条数据
@Test
public void testAdd() {
    User user = new User();
    user.setName("乐观锁");
    user.setAge(20);
    user.setEmail("1243@qq.com");
    int insert = userMapper.insert(user);
    System.out.println(insert);
}

添加后数据库如下

mysql> select * from user;
+---------------------+--------------+------+--------------------+---------------------+---------------------+---------+
| id                  | NAME         | age  | email              | create_time         | update_time         | version |
+---------------------+--------------+------+--------------------+---------------------+---------------------+---------+
|                   0 | auto         |   20 | 1243@qq.com        | NULL                | NULL                |    NULL |
|                   1 | Jone         |   18 | test1@baomidou.com | NULL                | NULL                |    NULL |
|                   2 | Jack         |   20 | test2@baomidou.com | NULL                | NULL                |    NULL |
|                   3 | Tom          |   28 | test3@baomidou.com | NULL                | NULL                |    NULL |
|                   4 | Sandy        |   21 | test4@baomidou.com | NULL                | NULL                |    NULL |
|                   5 | Billie       |   24 | test5@baomidou.com | NULL                | NULL                |    NULL |
| 1443158688033337346 | lucymaryupup |   20 | 1243@qq.com        | NULL                | 2021-09-30 08:51:12 |    NULL |
| 1443378040145903617 | ASSIGN_ID    |   20 | 1243@qq.com        | 2021-09-30 08:51:56 | 2021-09-30 08:51:56 |    NULL |
| 1444192337759502338 | 乐观锁       |   20 | 1243@qq.com        | 2021-10-02 14:47:40 | 2021-10-02 14:47:40 |       1 |
+---------------------+--------------+------+--------------------+---------------------+---------------------+---------+
9 rows in set (0.00 sec)

执行乐观锁的测试

// 测试乐观锁
@Test
public void testOptimisticLocker() {
    // 根据id查询
    User user = userMapper.selectById(1444192337759502338L);
    // 修改
    user.setName("zhangsan");
    userMapper.updateById(user);
}

执行后数据库如下

mysql> select * from user;
+---------------------+--------------+------+--------------------+---------------------+---------------------+---------+
| id                  | NAME         | age  | email              | create_time         | update_time         | version |
+---------------------+--------------+------+--------------------+---------------------+---------------------+---------+
|                   0 | auto         |   20 | 1243@qq.com        | NULL                | NULL                |    NULL |
|                   1 | Jone         |   18 | test1@baomidou.com | NULL                | NULL                |    NULL |
|                   2 | Jack         |   20 | test2@baomidou.com | NULL                | NULL                |    NULL |
|                   3 | Tom          |   28 | test3@baomidou.com | NULL                | NULL                |    NULL |
|                   4 | Sandy        |   21 | test4@baomidou.com | NULL                | NULL                |    NULL |
|                   5 | Billie       |   24 | test5@baomidou.com | NULL                | NULL                |    NULL |
| 1443158688033337346 | lucymaryupup |   20 | 1243@qq.com        | NULL                | 2021-09-30 08:51:12 |    NULL |
| 1443378040145903617 | ASSIGN_ID    |   20 | 1243@qq.com        | 2021-09-30 08:51:56 | 2021-09-30 08:51:56 |    NULL |
| 1444192337759502338 | zhangsan     |   20 | 1243@qq.com        | 2021-10-02 14:47:40 | 2021-10-02 14:55:10 |       2 |
+---------------------+--------------+------+--------------------+---------------------+---------------------+---------+
9 rows in set (0.00 sec)