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MyBatis-plus的介绍
MyBatis-plus是MyBatis的增强工具，在MyBatis的基础上做出加强，只要MyBatis有的功能MyBatis-plus都有。
MyBatis-plus的上手
添加依赖
在我们创建项目的时候，我们需要添加MyBatis-plus和mysql的依赖
MyBatis-plus的依赖
<dependency><groupId>com.baomidou</groupId><artifactId>mybatis-plus-boot-starter</artifactId><version>3.5.7</version></dependency>Mysql的依赖
<dependency><groupId>com.mysql</groupId><artifactId>mysql-connector-j</artifactId><scope>runtime</scope></dependency>配置数据库
spring:datasource:url: jdbc:mysql://127.0.0.1:3306/mybatis_test?characterEncoding=utf8&useSSL=false&allowPublicKeyRetrieval=true&serverTimezone=Asia/Shanghaiusername: rootpassword: 123456driver-class-name: com.mysql.cj.jdbc.Drivermybatis-plus:configuration:log-impl: org.apache.ibatis.logging.stdout.StdOutImplmapper-locations: "classpath*:/mapper/**.xml" # Mapper.xml首先我们创建UserInfo类
实体类中的属性和表中的字段要一一对应。
@Data
@TableName("user_info")
public class UserInfo {@TableId("id" )private Integer id;@TableField("username")private String username;private String password;private Integer age;private Integer gender;private String phone;private Integer deleteFlag;private Date createTime;private Date updateTime;
}编写一个Mapper接口
@Mapper
public interface UserInfoMapper extends BaseMapper<UserInfo> {MyBatis-plus提供一个基础的BaseMapper接口，已经实现了单表的增删改查，我们自己的Mapper接口只需要继承这个BaseMapper接口，就可以实现单表的增删改查了
CRUD
我们来简单的测试一下MyBatis-plus的CRUD
@SpringBootTest
class UserInfoMapperTest {@Autowiredprivate UserInfoMapper userInfoMapper;@Testvoid select() {userInfoMapper.selectById(1);}@Testvoid update() {UserInfo userInfo = new UserInfo();userInfo.setId(1);userInfo.setAge(12);userInfo.setPassword("5556666");userInfoMapper.updateById(userInfo);}@Testvoid insert() {UserInfo userInfo = new UserInfo();userInfo.setId(27);userInfo.setAge(3);userInfo.setPassword("3");userInfo.setUsername("123333");userInfoMapper.insert(userInfo);}@Testvoid delete() {userInfoMapper.deleteById(8);
}@TableName
修改实体类名UserInfo为Userinfo
我们可以用@TableName来标识实体类对应的表
@Data@TableName("user_info")public class Userinfo {private Integer id;private String username;private String password;private Integer age;private Integer gender;private String phone;private Integer deleteFlag;private Date createTime;private Date updateTime;}@TableField
修改属性名deleteFlag为deleteflag
@TableField("delete_flag")private Integer deleteflag;@TableId
修改属性名id为userId
我们可以通过@TableId来指定对应的主键
@TableId("id")private Integer userId;
条件构造器
QueryWrapper
⽤于构造查询条件,在AbstractWrapper的基础上拓展了⼀个select⽅法,允许指定查询字段，QueryWrapper并不只用于查询语句，无论是修改，删除，查询都可以使用QueryWrapper来构造条件
Select
SELECT id,username,password,age FROM user_info WHERE age = 18 AND username
"%min%" void selectByCondition() {QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>().select("username", "password", "id", "age").eq("age", 18).like("username", "min");List<UserInfo> userInfos = userInfoMapper.selectList(queryWrapper);userInfos.forEach(x -> System.out.println(x));}Update
UPDATE user_info SET delete_flag=? WHERE age < 20@Testvoid updateByCondition() {UserInfo userInfo = new UserInfo();userInfo.setDeleteFlag(1);QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>().lt("age", 20);userInfoMapper.update(userInfo, queryWrapper);}Delete
DELETE FROM user_info WHERE age = 18@Testvoid deleteByCondition(){QueryWrapper<UserInfo> queryWrapper =new QueryWrapper<UserInfo>().eq("age",18);userInfoMapper.delete(queryWrapper);}UpdateWrapper
对于更新,我们也可以直接使⽤UpdateWrapper,在不创建实体对象的情况下,直接设置更新字段和条件
UPDATE user_info SET delete_flag=0, age=5 WHERE id IN (1,2,3)@Testvoid updateByCondition2(){UpdateWrapper<UserInfo> updateWrapper=new UpdateWrapper<UserInfo>().set("delete_flag",0).set("age",5).in("id",List.of(1,2,3));userInfoMapper.update(updateWrapper);}
UPDATE user_info SET age = age+10 WHERE id IN (1,2,3)@Testvoid updateByCondition3(){UpdateWrapper<UserInfo> updateWrapper=new UpdateWrapper<UserInfo>().setSql("age=age+10").in("id",List.of(1,2,3));userInfoMapper.update(updateWrapper);}LambdaQueryWrapper
QueryWrapper和UpdateWrapper存在⼀个问题,就是需要写死字段名,如果字段名发⽣变更,可能会 因为测试不到位酿成事故。
MyBatis-Plus 给我们提供了⼀种基于Lambda表达式的条件构造器,它通过Lambda表达式来引⽤实体类的属性，从⽽避免了硬编码字段名,也提⾼了代码的可读性和可维护性。
@Testvoid selectByLambdaCondition() {QueryWrapper<UserInfo> queryWrapper=new QueryWrapper<UserInfo>();queryWrapper.lambda().select(UserInfo::getUsername,UserInfo::getPassword).eq(UserInfo::getAge,18);userInfoMapper.selectList(queryWrapper);}
LambdaUpdateWrapper
@Testvoid updateByLambdaCondition(){UpdateWrapper<UserInfo> updateWrapper=new UpdateWrapper<UserInfo>();updateWrapper.lambda().set(UserInfo::getUsername,"123").set(UserInfo::getAge,12).in(UserInfo::getId,List.of(1,2,3));userInfoMapper.update(updateWrapper);}
⾃定义SQL
在实际的开发中，MyBatis-plus提供的操作不能满足我们的实际需求，MyBatis-plus也提供了自定义SQL的功能，我们可以用Wrapper构造查询条件，结合Mapper编写SQL
select id,username,password,age FROM user_info WHERE username = "admin" @Select("select * from user_info ${ew.customSqlSegment}")List<UserInfo> queryUserByCustom(@Param(Constants.WRAPPER)Wrapper wrapper);@Testvoid testQueryUserByCustom(){QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>().eq("username","admin");userInfoMapper.queryUserByCustom(queryWrapper).forEach(System.out::println);}注：
参数命名：在⾃定义SQL时,传递Wrapper对象作为参数时,参数名必须为 ew 或者使⽤注解 ${ew.customSqlSegment}，明确指定参数为Wrapper对象
使用 ${ew.customSqlSegment} ：在SQL语句中，使⽤ ${ew.customSqlSegment}来引⽤Wrapper对象⽣成的SQL⽚段.
不⽀持基于entity的where语句：⾃定义SQL时，Wrapper对象不会基于实体类⾃动⽣成 where⼦句，你需要⼿动编写完整的SQL语句
MyBatis-plus也支持xml的方式
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.blame.mybatisplus.mapper.UserInfoMapper"><select id="queryUserByCustom2" resultType="com.blame.mybatisplus.model.UserInfo">select id,username,password,age FROM user_info ${ew.customSqlSegment}</select></mapper>List<UserInfo> queryUserByCustom2(@Param(Constants.WRAPPER)Wrapper<UserInfo> wrapper); @Testvoid testQueryUserByCustom2(){QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>().eq("username","admin");userInfoMapper.queryUserByCustom2(queryWrapper).forEach(System.out::println);}如果需要查看更多关于MyBatis-plus 的资料，点击
简介 | MyBatis-Plus
https://baomidou.com/introduce/
希望能对大家有所帮助！！！！！
