看完这篇，不信你还能不会用 MyBatis-Plus(一）

DROP TABLE IF EXISTS user;
CREATE TABLE user
(
 id BIGINT(20) NOT NULL COMMENT '主键ID',
 name VARCHAR(30) NULL DEFAULT NULL COMMENT '姓名',
 age INT(11) NULL DEFAULT NULL COMMENT '年龄',
 email VARCHAR(50) NULL DEFAULT NULL COMMENT '邮箱',
 PRIMARY KEY (id)
);

INSERT INTO user (id, name, age, email) VALUES
(1, 'Jone', 18, 'test1@baomidou.com'),
(2, 'Jack', 20, 'test2@baomidou.com'),
(3, 'Tom', 28, 'test3@baomidou.com'),
(4, 'Sandy', 21, 'test4@baomidou.com'),
(5, 'Billie', 24, 'test5@baomidou.com');

<dependency>
      <groupId>com.baomidou</groupId>
      <artifactId>mybatis-plus-boot-starter</artifactId>
      <version>Latest Version</version>
</dependency>

spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
#mysql 8 需要配置时区，不然会出现启动报错的情况   serverTimezone=GMT%2B8
spring.datasource.url=jdbc:mysql://localhost:3306/mybatis_plus?serverTimezone=GMT%2B8&useSSL=true&useUnicode=true&characterEncoding=utf8
spring.datasource.username=root
spring.datasource.password=233031

/*用户实体类*/
public class User {
    private Long id;
    private String name;
    private Integer age;
    private String email;
    //构造方法
    //GET、Set方法
}

/*在对应的Mapper上面继承基本的类 BaseMapper*/
@Repository
public interface UserMapper extends BaseMapper<User> {
    /*所有的CRUD已经编写完成*/
}
//写@Repository注解，需要在主类添加MapperScan扫描mapper包
//写@Mapper则不需要

#配置日志
mybatis-plus.configuration.log-impl=org.apache.ibatis.logging.stdout.StdOutImpl

//测试插入
@Test
public void testInsert(){
    User user = new User();
    user.setName("派大星学Java");
    user.setAge(16);
    user.setEmail("none-j@qq.com");
    int insert = userMapper.insert(user);//帮我们自动生成id
    System.out.println(insert);//受影响的行数
    System.out.println(user);//发现，id会自动回填
}

public enum IdType{
    AUTO(0),//数据库id自增
    NONE(1),//未设置主键 
    INPUT(2),//手动输入   一旦手动输入id之后，就需要自己设置id了
    ID_WORKER(3),//默认的全局唯一id
    UUID(4),//全局唯一id UUID
    ID_WORKER_STR(5),//ID_WORKER 字符串表示法
}

//更新操作
@Test
public void updateTest(){
    User user = new User();
    user.setId(5L);
    user.setName("我想创建公众号");
    user.setAge(16);
    int i = userMapper.updateById(user);
    System.out.println(i);
}

private Date createTime;
private Date updateTime;

//字段添加填充内容
@TableField(fill = FieldFill.INSERT)
private Date createTime;
@TableField(fill = FieldFill.INSERT_UPDATE)
private Date updateTime;

@Slf4j//日志
@Component
public class MyDateObjectHandler implements MetaObjectHandler {
    //插入时的填充策略
    @Override
    public void insertFill(MetaObject metaObject) {
        this.setFieldValByName("createTime",new Date(),metaObject);
        this.setFieldValByName("updateTime",new Date(),metaObject);
    }
    //更新时的填充策略
    @Override
    public void updateFill(MetaObject metaObject) {
        this.setFieldValByName("updateTime",new Date(),metaObject);
    }
}

--A
update user set name = "wumao",version = version + 1
where id = 2 and version = 1
--B  线程抢先完成，这个时候 version = 2，会导致A修改失败
update user set name = "wumao",version = version + 1
where id = 2 and version = 1

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

@MapperScan("com.pdx.mapper")//扫描mapper文件夹
@EnableTransactionManagement
@Configuration//配置类
public class MyBatisPlusConfig  {
    @Bean
    public OptimisticLockerInterceptor optimisticLockerInterceptor() {
        return new OptimisticLockerInterceptor();
    }
}

//测试乐观锁
//成功案例
@Test
public void versionTest(){
    User user = userMapper.selectById(1L);
    user.setName("派大星");
    user.setEmail("admin@qq.com");
    userMapper.updateById(user);
}
//乐观锁失败案例----多线程
@Test
public void OptimisticLockerTest(){
    User user = userMapper.selectById(1L);
    user.setName("派大星111");
    user.setEmail("admin@qq.com");
    //模拟另外一个线程执行了插队操作
    User user2 = userMapper.selectById(1L);
    user.setName("派大星222");
    user.setEmail("admin@qq.com");
    userMapper.updateById(user2);
    userMapper.updateById(user);
}

//查询操作
@Test
public void testSelect(){
    User user = userMapper.selectById(1L);
    System.out.println(user);
}
//批量查询
@Test
public void testBatchList(){
    List<User> users = userMapper.selectBatchIds(Arrays.asList(1, 2, 3));
    users.forEach(System.out::println);
}
//按条件查询 map操作
@Test
public void testSelectMap(){
    HashMap<String, Object> map = new HashMap<>();
    map.put("name","派大星");
    map.put("age",16);
    List<User> users = userMapper.selectByMap(map);
    users.forEach(System.out::println);
}