mybatis plus一对多查询（经典案例）

傷城~ 2023-10-06 22:06 3阅读 0赞

### 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

![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5Y-r5oiR6ICB5Lyv_size_20_color_FFFFFF_t_70_g_se_x_16][]

学生student

![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5Y-r5oiR6ICB5Lyv_size_20_color_FFFFFF_t_70_g_se_x_16 1][]

### 二、代码实现 ###

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

实体类ClassInfo.java

@Data
    public class ClassInfo {
    
        private Long id;
        private String name;
        private String nameTest;
    
        private List<Student> 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">
    
    <mapper namespace="com.example.demo.mapper.ClassInfoMapper">
    
        
    
        
        <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<ClassInfo> {
    
    
        IPage<ClassInfo> listAllWithStudent(IPage<ClassInfo> page);
    
    }

ClassInfoService.java

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

ClassInfoServiceImpl.java

@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);
        }
    }

ClassInfoController.java

@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);
        }
    
    }

[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5Y-r5oiR6ICB5Lyv_size_20_color_FFFFFF_t_70_g_se_x_16]: https://img-blog.csdnimg.cn/9bd59345da1d4177b51feb4249063ea1.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBA5Y-r5oiR6ICB5Lyv,size_20,color_FFFFFF,t_70,g_se,x_16
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5Y-r5oiR6ICB5Lyv_size_20_color_FFFFFF_t_70_g_se_x_16 1]: https://img-blog.csdnimg.cn/2bb4e9235020446791d8e059b32cb8c9.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBA5Y-r5oiR6ICB5Lyv,size_20,color_FFFFFF,t_70,g_se,x_16