MyBatisPlus（七）乐观锁

使用乐观锁的意图是：当要更新一条记录的时候，希望这条记录没有被别人更新。那么需要在表中增加一个字段version来实现。

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

而MyBatisPlus已经封装好了乐观锁的实现，我们来配置使用即可

乐观锁配置

配置乐观锁需要2步：

1. 在mybatisPlusInterceptor()配置中，增加一行乐观锁插件配置即可：interceptor.addInnerInterceptor(new OptimisticLockerInnerInterceptor());

@Bean
public MybatisPlusInterceptor mybatisPlusInterceptor() {
   
    MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
    interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL)); // 分页插件
    interceptor.addInnerInterceptor(new OptimisticLockerInnerInterceptor()); // 乐观锁插件
    return interceptor;
}

1. 在实体类version字段中增加注解@Version

@Version
private Integer version;

测试代码

我们来试一下，将部门根据ID查询出来，修改其名称，并根据ID进行更新操作

@Test
public void testUpdateById() {
   
    Dept dept = deptMapper.selectById("4b0e878b5bfc2f22f44f1a3691403116");
    dept.setName("Lilei");
    int result = deptMapper.updateById(dept);
    System.out.println(result);
}

执行日志：

JDBC Connection [HikariProxyConnection@233271858 wrapping com.mysql.cj.jdbc.ConnectionImpl@62628e78] will not be managed by Spring
==>  Preparing: SELECT id,name,deleted,version,create_time,update_time FROM dept WHERE id=? AND deleted=0
==> Parameters: 4b0e878b5bfc2f22f44f1a3691403116(String)
<==    Columns: id, name, deleted, version, create_time, update_time
<==        Row: 4b0e878b5bfc2f22f44f1a3691403116, Lilei, 0, 6, null, null
<==      Total: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@511505e7]
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@743c6ce4] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@532297836 wrapping com.mysql.cj.jdbc.ConnectionImpl@62628e78] will not be managed by Spring
==>  Preparing: UPDATE dept SET name=?, version=? WHERE id=? AND version=? AND deleted=0
==> Parameters: Lilei(String), 7(Integer), 4b0e878b5bfc2f22f44f1a3691403116(String), 6(Integer)
<==    Updates: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@743c6ce4]
1

从执行日志中可以看出会增加 set version = newVersion where version = oldVersion，表示乐观锁成功使用。为了进一步验证，我们模拟一个错误的执行

    @Test
    public void testUpdateById2() {
   
        Dept dept1 = deptMapper.selectById("4b0e878b5bfc2f22f44f1a3691403116");
        dept1.setName("Lilei1");

        Dept dept2 = deptMapper.selectById("4b0e878b5bfc2f22f44f1a3691403116");
        dept2.setName("Lilei2");

        int result = deptMapper.updateById(dept1);
        System.out.println(result);

        int result2 = deptMapper.updateById(dept2);
        System.out.println(result2);
    }

执行日志：

JDBC Connection [HikariProxyConnection@1491623023 wrapping com.mysql.cj.jdbc.ConnectionImpl@a137d7a] will not be managed by Spring
==>  Preparing: SELECT id,name,deleted,version,create_time,update_time FROM dept WHERE id=? AND deleted=0
==> Parameters: 4b0e878b5bfc2f22f44f1a3691403116(String)
<==    Columns: id, name, deleted, version, create_time, update_time
<==        Row: 4b0e878b5bfc2f22f44f1a3691403116, Lilei, 0, 7, null, null
<==      Total: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@2a389173]
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@3bbf9027] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@281151050 wrapping com.mysql.cj.jdbc.ConnectionImpl@a137d7a] will not be managed by Spring
==>  Preparing: SELECT id,name,deleted,version,create_time,update_time FROM dept WHERE id=? AND deleted=0
==> Parameters: 4b0e878b5bfc2f22f44f1a3691403116(String)
<==    Columns: id, name, deleted, version, create_time, update_time
<==        Row: 4b0e878b5bfc2f22f44f1a3691403116, Lilei, 0, 7, null, null
<==      Total: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@3bbf9027]
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@108d55c4] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@404152906 wrapping com.mysql.cj.jdbc.ConnectionImpl@a137d7a] will not be managed by Spring
==>  Preparing: UPDATE dept SET name=?, version=? WHERE id=? AND version=? AND deleted=0
==> Parameters: Lilei1(String), 8(Integer), 4b0e878b5bfc2f22f44f1a3691403116(String), 7(Integer)
<==    Updates: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@108d55c4]
1
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@7ee3d262] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@60221145 wrapping com.mysql.cj.jdbc.ConnectionImpl@a137d7a] will not be managed by Spring
==>  Preparing: UPDATE dept SET name=?, version=? WHERE id=? AND version=? AND deleted=0
==> Parameters: Lilei2(String), 8(Integer), 4b0e878b5bfc2f22f44f1a3691403116(String), 7(Integer)
<==    Updates: 0
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@7ee3d262]
0

从日志中我们可以看出，第一个update语句执行了，而第二个没有执行，验证成功。

特别说明

乐观锁特别说明：

• 支持的数据类型只有:int,Integer,long,Long,Date,Timestamp,LocalDateTime
• 整数类型下 newVersion = oldVersion + 1
• newVersion 会回写到 entity 中
• 仅支持 updateById(id) 与 update(entity, wrapper) 方法
• 在 update(entity, wrapper) 方法下, wrapper 不能复用!!!

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