4_多对多关联查询

4_多对多关联查询

根据项目编号查询项目信息,以及参与到该项目之中的所有的员工信息

实体类

1. @NoArgsConstructor
2. @AllArgsConstructor
3. @Data
4. public class Project implements Serializable {
5. private Integer pid;
6. private String pname;
7. private Integer money;
8. // 组合一个ProjectRecord对象集合作为属性
9. private List projectRecords;
10. }
11. @Data
12. @AllArgsConstructor
13. @NoArgsConstructor
14. public class ProjectRecord implements Serializable {
15. private Integer empno;
16. private Integer pid;
17. // 组合一个Emp对象作为属性
18. private Emp emp;
19. }

接口

1. package com.msb.mapper;
2. import com.msb.pojo.Emp;
3. import com.msb.pojo.Project;
4. /**
5. • @Author: Ma HaiYang
6. • @Description: MircoMessage:Mark_7001
7. */
8. public interface ProjectMapper {
9. /**
10. * 根据项目编号查询一个项目信息及参与该项目的所有员工信息
11. * @param pid 项目编号
12. * @return 所有信息封装的Project对象
13. */
14. Project findProjectJoinEmpsByPid(int pid);
15. }

映射文件

3. PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
4. "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
28. select * from project p left join projectrecord pr on p.pid = pr.pid left join emp e on e.empno = pr.empno where p.pid= #

测试代码

1. @Test
2. public void testManyToMany() throws ParseException {
3. ProjectMapper mapper = sqlSession.getMapper(ProjectMapper.class);
4. Project project = mapper.findProjectJoinEmpsByPid(2);
5. System.out.println(project.getPid());
6. System.out.println(project.getPname());
7. System.out.println(project.getMoney());
8. List projectRecords = project.getProjectRecords();
9. for (ProjectRecord projectRecord : projectRecords) {
10. Emp emp = projectRecord.getEmp();
11. System.out.println(emp);
12. }
13. }

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