MybatisPlus实现对象嵌套关联查询一对多List集合查询

@Data

@TableName ( "tb_user" )

public class User {

    @TableId (type= IdType.INPUT)

    private String id;

    @TableField ( "user_name" )

    private String username;

    private String password;

    private String name;

    private String email;

    private int age;

    private ArrayList<Authority> list;

}

@Data

@TableName

public class Authority {

    @TableId (type = IdType.INPUT)

    @TableField ( "aid" )

    private int id;

    @TableId ( "aname" )

    private String name;

}

  @Test

    public void ManyToMany(){

        User user = userMapper.selectAuthorityById( 1 );

        ArrayList <Authority> list = user.getList();

        System.out.println(user);

        for (Authority authority : list) {

            System.out.println( "所对应权限为" +authority.getName());

        }

    }

        < dependency >

        < groupId >org.springframework.boot</ groupId >

        < artifactId >spring-boot-starter</ artifactId >

    </ dependency >

        < dependency >

        < groupId >mysql</ groupId >

        < artifactId >mysql-connector-java</ artifactId >

        < version >5.1.26</ version >

    </ dependency >

        < dependency >

        < groupId >org.projectlombok</ groupId >

        < artifactId >lombok</ artifactId >

        < optional >true</ optional >

    </ dependency >

        < dependency >

        < groupId >org.springframework.boot</ groupId >

        < artifactId >spring-boot-starter-test</ artifactId >

        < scope >test</ scope >

    </ dependency >

        <!--mybatis plus 起步依赖-->

        < dependency >

        < groupId >com.baomidou</ groupId >

        < artifactId >mybatis-plus-boot-starter</ artifactId >

        < version >3.4.0</ version >

    </ dependency >

< mapper namespace = "com.itheima.mybatisplus.mapper.UserMapper" >

    <!--返回的对象为authority-->

    < resultMap id = "authority" type = "com.itheima.mybatisplus.domain.User" >

        < id column = "id" property = "id" />

        < id column = "password" property = "password" />

        < id column = "age" property = "age" />

        < id column = "email" property = "email" />

        < id column = "name" property = "name" />

        < id column = "user_name" property = "username" />

      < collection property = "list"

                  ofType = "com.itheima.mybatisplus.domain.Authority" >

          < id property = "id" column = "aid" />

          < id property = "name" column = "aname" />

      </ collection >

     < select id = "selectAuthorityById" parameterType = "int" resultMap = "authority" >

        SELECT * FROM

          authority a,tb_user t,user_authority ua

          WHERE a.aid=ua.authority_id

          AND t.id=ua.user_id

          AND t.id=#{id}

    </ select >

<!--        多对一  或者 一对一   -->

<!--        <association property=""-->

<!--        一对多 返回集合-->

<!- -  < collection   property = "" - ->

@Data

public class ClassInfo {

     private Long id;

     private String name;

     private String nameTest;

     private List<Student> studentList;

}

<? 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">

<!--名称空间：对应mapper层某个接口的包的全名称-->

< mapper namespace = "com.example.demo.mapper.ClassInfoMapper" >

     <!--    查询班级 返回所有学生的信息   一对多-->

     <!--    自定义映射规则-->

     < resultMap id = "OneToMany" type = "com.qcby.zsgc.entity.ClassInfo" >

         < result column = "name" jdbcType = "VARCHAR" property = "nameTest" />

         < collection   column = "{id1=id,name=name}"

                      property = "studentList"

                      select = "com.example.demo.mapper.StudentMapper.listByClassInfoId" >                 </ collection >

     </ resultMap >

     < select id = "listAllWithStudent" resultMap = "OneToMany" >

         select * from class_info

     </ select >

< select id = "listByClassInfoId" resultType = "com.example.demo.entity.Student" >

        SELECT

           *

        FROM

            student s

        where class_info_id = #{id1} or name = #{name}

    </ select >

public interface ClassInfoMapper extends BaseMapper<ClassInfo> {  

    IPage<ClassInfo> listAllWithStudent(IPage<ClassInfo> page); 

}

public interface ClassInfoService extends IService<ClassInfo> { 

    IPage<ClassInfo> listAllWithStudent(IPage<ClassInfo> page); 

}

@Service

public class ClassInfoServiceImpl extends ServiceImpl<ClassInfoMapper, ClassInfo> implements ClassInfoService {

    @Autowired

    private StudentService studentService;

    @Override

    public IPage<ClassInfo> listAllWithStudent(IPage<ClassInfo> page) {

        return this .baseMapper.listAllWithStudent(page);

    }

}

@Controller

@RequestMapping ( "classInfo" )

public class ClassInfoController {

    @Autowired

    private ClassInfoService classInfoService;

    @RequestMapping ( "listAllWithStudent" )

    @ResponseBody

    public IPage<ClassInfo> listAllWithStudent(Integer pageNo,Integer pageSize){

        Page<ClassInfo> page = new Page<>(pageNo,pageSize);

        return classInfoService.listAllWithStudent(page);

    } 

}