MybatisPlus入门（中）-阿里云开发者社区

MybatisPlus入门（上）+https://developer.aliyun.com/article/1492260

自动填充

创建时间、修改时间、这些个操作都是自动化完成的，我们不希望手动更新！

阿里巴巴开发手册：所有的数据库表：gmt_create、gmt_modified 几乎所有表都要配置上，且是自动化的。

方式一：数据库级别（工作中不允许操作数据库）

1、在表中新增字段 create_time、update_time

2、再次测试插入方式，需要把实体类进行同步

private Date createTime;
private Date updateTime;

3、再次更新，查看结果, 代码未更新，数据库自动发生更新

方式二：代码级别

1、删除数据库的默认值、更新操作！

2、实体类字段属性上增加注解。

package com.jay.mybatisplus.pojo;
import com.baomidou.mybatisplus.annotation.FieldFill;
import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.apache.ibatis.annotations.Insert;
import java.util.Date;
/**
 * @author : Jay
 * @description : 用户
 * @date : 2021-09-24 11:26
 **/
@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    @TableId(type = IdType.AUTO)
    private Long id;
    private String name;
    private Integer age;
    private String email;
    /**
     * 新增时填充创建时间
     */
    @TableField(fill = FieldFill.INSERT)
    private Date createTime;
    /**
     * 更新或第一次新增时填充更新时间
     */
    @TableField(fill = FieldFill.INSERT_UPDATE)
    private Date updateTime;
}

3、编写处理器来处理这个注解即可！

package com.jay.mybatisplus.handler;
import com.baomidou.mybatisplus.core.handlers.MetaObjectHandler;
import lombok.extern.slf4j.Slf4j;
import org.apache.ibatis.reflection.MetaObject;
import org.springframework.stereotype.Component;
import java.time.LocalDateTime;
/**
 * @author : Jay
 * @description : 自动填充处理器
 * @date : 2021-09-24 14:15
 **/
@Slf4j
@Component
public class MyMetaObjectHandler implements MetaObjectHandler {
    /**
     * 插入时的填充策略
     * @param metaObject 数据对象
     */
    @Override
    public void insertFill(MetaObject metaObject) {
        log.info("start insert fill...");
        this.setFieldValByName("createTime", LocalDateTime.now(), metaObject);
        this.setFieldValByName("updateTime", LocalDateTime.now(), metaObject);
    }
    /**
     * 更新时的填充策略
     * @param metaObject
     */
    @Override
    public void updateFill(MetaObject metaObject) {
        log.info("start update fill...");
        this.setFieldValByName("updateTime", LocalDateTime.now(), metaObject);
    }
}

乐观锁

当要更新一条记录的时候，希望这条记录没有被别人更新

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

举例：

1、先查询，获取当前的版本号 version = 1
-- A用户
update user set name = "jay", version = version + 1 where id = 2 and version = 1;
-- B用户 的线程抢先完成，这个时候version=2，会导致A修改失败！
update user set name = "jay", version = version + 1 where id = 2 and version = 1;

测试乐观锁插件

1、增加乐观锁字段

2、实体类加对应的字段

/**
 * 乐观锁version注解
 */
@Version
private Integer version;

3、注册组件

package com.jay.mybatisplus.config;
import com.baomidou.mybatisplus.extension.plugins.OptimisticLockerInterceptor;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.transaction.annotation.EnableTransactionManagement;
/**
 * @author : Jay
 * @description : 配置累
 * @date : 2021-09-24 14:45
 **/
//从启动类迁移到mybatisPlus的配置类
@MapperScan("com.jay.mybatisplus.mapper")
//开启事务
@EnableTransactionManagement
@Configuration
public class MyBatisPlusConfig {
    /**
     * 注册乐观锁
     */
    @Bean
    public OptimisticLockerInterceptor optimisticLockerInterceptor() {
        return new OptimisticLockerInterceptor();
    }
}

4、测试日志及结果

正常的成功：

@Test
    void testOptimisticSuccess() {
        //1-查询用户信息
        User user = userMapper.selectById(1);
        //2-修改用户信息
        user.setName("Jay123");
        user.setAge(220);
        userMapper.updateById(user);
    }

Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@44af588b] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@1870234754 wrapping com.mysql.cj.jdbc.ConnectionImpl@332bcab0] will not be managed by Spring
==>  Preparing: SELECT id,name,age,email,version,create_time,update_time FROM user WHERE id=? 
==> Parameters: 1(Integer)
<==    Columns: id, name, age, email, version, create_time, update_time
<==        Row: 1, Jone, 18, test1@baomidou.com, 1, 2021-09-24 13:49:18, null
<==      Total: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@44af588b]
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@7f9fc8bd] was not registered for synchronization because synchronization is not active
2021-09-24 14:57:26.557  INFO 2774 --- [           main] c.j.m.handler.MyMetaObjectHandler        : start update fill...
JDBC Connection [HikariProxyConnection@365201320 wrapping com.mysql.cj.jdbc.ConnectionImpl@332bcab0] will not be managed by Spring
==>  Preparing: UPDATE user SET name=?, age=?, email=?, version=?, create_time=?, update_time=? WHERE id=? AND version=? 
==> Parameters: Jay123(String), 220(Integer), test1@baomidou.com(String), 2(Integer), 2021-09-24 13:49:18.0(Timestamp), 2021-09-24 14:57:26.557(Timestamp), 1(Long), 1(Integer)
<==    Updates: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@7f9fc8bd]

失败的情况：

@Test
void testOptimisticFail() {
    //用户1查询用户信息
    User user = userMapper.selectById(1);
    user.setName("Jay");
    user.setAge(230);
    //用户2查询用户信息
    User user1 = userMapper.selectById(1);
    user1.setName("lpp");
    user1.setAge(220);
    //用户2修改用户信息
    userMapper.updateById(user1);
    //用户1更新用户信息
    userMapper.updateById(user);
}

Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@3d19d85] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@858507952 wrapping com.mysql.cj.jdbc.ConnectionImpl@633cc6b5] will not be managed by Spring
==>  Preparing: SELECT id,name,age,email,version,create_time,update_time FROM user WHERE id=? 
==> Parameters: 1(Integer)
<==    Columns: id, name, age, email, version, create_time, update_time
<==        Row: 1, Jay123, 220, test1@baomidou.com, 2, 2021-09-24 13:49:18, 2021-09-24 14:57:27
<==      Total: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@3d19d85]
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@75e09567] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@708004780 wrapping com.mysql.cj.jdbc.ConnectionImpl@633cc6b5] will not be managed by Spring
==>  Preparing: SELECT id,name,age,email,version,create_time,update_time FROM user WHERE id=? 
==> Parameters: 1(Integer)
<==    Columns: id, name, age, email, version, create_time, update_time
<==        Row: 1, Jay123, 220, test1@baomidou.com, 2, 2021-09-24 13:49:18, 2021-09-24 14:57:27
<==      Total: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@75e09567]
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@3ddeaa5f] was not registered for synchronization because synchronization is not active
2021-09-24 15:04:20.322  INFO 2817 --- [           main] c.j.m.handler.MyMetaObjectHandler        : start update fill...
JDBC Connection [HikariProxyConnection@1208702946 wrapping com.mysql.cj.jdbc.ConnectionImpl@633cc6b5] will not be managed by Spring
==>  Preparing: UPDATE user SET name=?, age=?, email=?, version=?, create_time=?, update_time=? WHERE id=? AND version=? 
==> Parameters: lpp(String), 220(Integer), test1@baomidou.com(String), 3(Integer), 2021-09-24 13:49:18.0(Timestamp), 2021-09-24 15:04:20.322(Timestamp), 1(Long), 2(Integer)
<==    Updates: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@3ddeaa5f]
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@443faa85] was not registered for synchronization because synchronization is not active
2021-09-24 15:04:20.330  INFO 2817 --- [           main] c.j.m.handler.MyMetaObjectHandler        : start update fill...
JDBC Connection [HikariProxyConnection@518290846 wrapping com.mysql.cj.jdbc.ConnectionImpl@633cc6b5] will not be managed by Spring
==>  Preparing: UPDATE user SET name=?, age=?, email=?, version=?, create_time=?, update_time=? WHERE id=? AND version=? 
==> Parameters: 刘平平(String), 230(Integer), test1@baomidou.com(String), 3(Integer), 2021-09-24 13:49:18.0(Timestamp), 2021-09-24 15:04:20.33(Timestamp), 1(Long), 2(Integer)
<==    Updates: 0
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@443faa85]
2021-09-24 15:04:20.349  INFO 2817 --- [extShutdownHook] o.s.s.concurrent.ThreadPoolTaskExecutor  : Shutting down ExecutorService 'applicationTaskExecutor'
2021-09-24 15:04:20.350  INFO 2817 --- [extShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown initiated...
2021-09-24 15:04:20.363  INFO 2817 --- [extShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown completed.
Process finished with exit code 0

查询操作

/**
 * 普通查询
 */
@Test
void selectById(){
    User user = userMapper.selectById(1);
    System.out.println(user);
}
/**
 * 批量查询
 */
@Test
void selectByList(){
    List<User> users = userMapper.selectBatchIds(Arrays.asList(1, 2, 3));
    users.forEach(System.out::println);
}
/**
 * 多条件查询
 */
@Test
void selectByMap(){
    Map<String, Object> map = new HashMap<>();
    map.put("name","断言");
    map.put("age",24);
    List<User> users = userMapper.selectByMap(map);
    users.forEach(System.out::println);
}

分页查询

分页的通常方式

1、原始的limit进行分页。

2、pageHelper第三方插件。

3、MP其实也内置来分页插件！

MybatisPlus入门（下）+https://developer.aliyun.com/article/1492264

MybatisPlus入门（中）