一、条件
查询班级表 返回所有学生信息 （一对多问题）
二、数据库
班级class_info

学生student

二、代码实现

<!--        多对一  或者 一对一   -->
<!--        <association property=""-->

<!--        一对多 返回集合-->
<!- -  <collection  property=""- ->

实体类ClassInfo.java

@Data
public class ClassInfo {
 
    private Long id;
    private String name;
    private String nameTest;
 
    private List studentList;
}

ClassInfoMapper.xml

<?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>

关联StudentMapper.xml中的子查询

 <select id="listByClassInfoId" resultType="com.example.demo.entity.Student">
        SELECT
           *
        FROM
            student s
        where class_info_id = #{id1} or name = #{name}
    </select>

ClassInfoMapper.java

public interface ClassInfoMapper extends BaseMapper {
 
 
    IPage listAllWithStudent(IPage page);
 
}

ClassInfoService.java

public interface ClassInfoService extends IService {
 
    IPage listAllWithStudent(IPage page);
 
}

ClassInfoServiceImpl.java

@Service
public class ClassInfoServiceImpl extends ServiceImpl implements ClassInfoService {
    @Autowired
    private StudentService studentService;
    @Override
    public IPage listAllWithStudent(IPage page) {
        return this.baseMapper.listAllWithStudent(page);
    }
}

ClassInfoController.java

@Controller
@RequestMapping("classInfo")
public class ClassInfoController {
 
    @Autowired
    private ClassInfoService classInfoService;
 
    @RequestMapping("listAllWithStudent")
    @ResponseBody
    public IPage listAllWithStudent(Integer pageNo,Integer pageSize){
        Page page = new Page<>(pageNo,pageSize);
        return classInfoService.listAllWithStudent(page);
    }
 
}