1. 简介

官网 https://mybatisplusjoin.com/

2. 基本用法

步骤：

1. 添加依赖

   <!--mybatis-plus-join-->
   <dependency><groupId>com.github.yulichang</groupId><artifactId>mybatis-plus-join-boot-starter</artifactId><version>1.4.5</version>
   </dependency>

2. 编辑EmpMapper.java，继承自MPJBaseMapper

   public interface EmpMapper extends MPJBaseMapper<Emp> {
   }

3. 测试

   @SpringBootTest
   class EmpMapperTest {
   ​@Resourceprivate EmpMapper empMapper;
   ​@Testpublic void selectAll(){MPJLambdaWrapper<Emp> wrapper = new MPJLambdaWrapper<Emp>().selectAll(Emp.class) // 查询Emp类的所有字段.selectAs(Dept::getName, EmpDTO::getDeptName)// 查询Dept类的name字段.leftJoin(Dept.class, Dept::getId, Emp::getDeptId) // 左连接.orderByDesc(Emp::getId);
   ​List<EmpDTO> list = empMapper.selectJoinList(EmpDTO.class, wrapper);list.forEach(System.out::println);}
   ​@Testpublic void selectByPage(){Page<EmpDTO> page = new Page<>(1, 3);
   ​empMapper.selectJoinPage(page, EmpDTO.class,new MPJLambdaWrapper<Emp>().selectAll(Emp.class).selectAs(Dept::getName, EmpDTO::getDeptName).leftJoin(Dept.class, Dept::getId, Emp::getDeptId).eq(Dept::getId, 1));
   ​page.getRecords().forEach(System.out::println);}
   ​
   }