一对多和多对一处理

MegaDataFlowers2026-03-16 11:39

参考视频：【狂神说Java】Mybatis最新完整教程IDEA版通俗易懂 点击观看

文章目录

数据库设计

sql 复制代码 
CREATE TABLE `teacher` (
  `id` INT(10) NOT NULL,
  `name` VARCHAR(30) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8;
INSERT INTO teacher(`id`, `name`) VALUES (1, '秦老师');
CREATE TABLE `student` (
  `id` INT(10) NOT NULL,
  `name` VARCHAR(30) DEFAULT NULL,
  `tid` INT(10) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `fktid` (`tid`),
  CONSTRAINT `fktid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8;
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('1', '小明', '1');
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('2', '小红', '1');
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('3', '小张', '1');
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('4', '小李', '1');
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('5', '小王', '1');
select * from teacher;
select * from student;

核心配置文件

xml 复制代码 
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<!--configuration核心配置文件-->
<configuration>
    <!--引入外部配置文件-->
    <properties resource="db.properties"/>
    <settings>
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>
    <!--给实体类起别名-->
    <typeAliases>
        <typeAlias type="com.findx.pojo.Teacher" alias="Teacher"/>
        <typeAlias type="com.findx.pojo.Student" alias="Student"/>
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <!-- MySQL 8 驱动类：多了 .cj -->
                <property name="driver" value="${driver}"/>
                <!-- MySQL 8 URL：增加了 serverTimezone 参数 -->
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper class="com.findx.dao.TeacherMapper"/>
        <mapper class="com.findx.dao.StudentMapper"/>
    </mappers>
</configuration>

多对一的处理

多个学生对应一个老师

实体类

java 复制代码 
package com.findx.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Student {
    private int id;
    private String name;
    //学生需要关联一个老师
    //private int tid;
    private Teacher teacher;
}
java 复制代码 
package com.findx.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Teacher {
    private int id;
    private String name;
}

按照查询嵌套处理

1、StudentMapper和TeacherMapper接口

java 复制代码 
package com.findx.dao;

import com.findx.pojo.Student;
import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface StudentMapper {
    //查询所有的学生信息以及对应的老师信息
    //select s.id,s.name,t.name from student s,teacher t where s.tid = t.id;
    public List<Student> getStudent();
}
java 复制代码 
package com.findx.dao;

import com.findx.pojo.Teacher;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;

public interface TeacherMapper {
    @Select("select * from mybatis.teacher where id = #{tid}")
    Teacher getTeacher(@Param("tid") int id);
}

2、StudentMapper.xml文件

xml 复制代码 
<?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">
<!--configuration核心配置文件-->
<mapper namespace="com.findx.dao.StudentMapper">
    <!--
    查询所有学生信息以及对应的老师信息
    select s.id,s.name,t.name from student s,teacher t where s.tid = t.id;
    1):查询所有的学生信息
    2):根据查询出来的学生的tid寻找对应的老师
    -->
    <select id="getStudent" resultMap="StudentTeacher">
        select * from mybatis.student;
    </select>
    <resultMap id="StudentTeacher" type="Student">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <!--复杂的属性需要单独处理-->
        <!--如果是一个对象使用association-->
        <association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
        <!--如果一个集合使用collection-->
    </resultMap>
    <select id="getTeacher" resultType="Teacher">
        select * from mybatis.teacher where id = #{id}
    </select>
</mapper>

3、测试代码

java 复制代码 
package com.findx.dao;

import com.findx.pojo.Student;
import com.findx.pojo.Teacher;
import com.findx.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class MapperTest {
    @Test
    public void getTeacher() {
        //获取SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //执行方法
        TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
        Teacher teacher = mapper.getTeacher(1);
        System.out.println(teacher);
        //关闭SqlSession
        sqlSession.close();
    }
    @Test
    public void getStudent() {
        //获取SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //执行方法
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        List<Student> studentList = mapper.getStudent();
        for (Student student : studentList) {
            System.out.println(student);
        }
        //关闭SqlSession
        sqlSession.close();
    }
}

按照结果嵌套处理

1、StudentMapper接口

java 复制代码 
package com.findx.dao;

import com.findx.pojo.Student;
import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface StudentMapper {
    //查询所有的学生信息以及对应的老师信息
    //select s.id,s.name,t.name from student s,teacher t where s.tid = t.id;
    public List<Student> getStudent();
    public List<Student> getStudent2();
}

2、StudentMapper.xml文件

xml 复制代码 
<?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">
<!--configuration核心配置文件-->
<mapper namespace="com.findx.dao.StudentMapper">
    <!--
    查询所有学生信息以及对应的老师信息
    select s.id,s.name,t.name from student s,teacher t where s.tid = t.id;
    1):查询所有的学生信息
    2):根据查询出来的学生的tid寻找对应的老师
    -->
    <select id="getStudent" resultMap="StudentTeacher">
        select * from mybatis.student;
    </select>
    <resultMap id="StudentTeacher" type="Student">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <!--复杂的属性需要单独处理-->
        <!--如果是一个对象使用association-->
        <association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
        <!--如果一个集合使用collection-->
    </resultMap>
    <select id="getTeacher" resultType="Teacher">
        select * from mybatis.teacher where id = #{id}
    </select>

    <!--按照结果嵌套处理-->
    <select id="getStudent2" resultMap="StudentTeacher2">
        select s.id sid,s.name sname,t.name tname
        from student s,teacher t
        where s.tid = t.id;
    </select>
    <resultMap id="StudentTeacher2" type="Student">
        <id property="id" column="sid"/>
        <result property="name" column="sname"/>
        <association property="teacher" javaType="Teacher">
            <result property="name" column="tname"/>
        </association>
    </resultMap>
</mapper>

3、测试代码

java 复制代码 
package com.findx.dao;

import com.findx.pojo.Student;
import com.findx.pojo.Teacher;
import com.findx.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class MapperTest {
    @Test
    public void getTeacher() {
        //获取SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //执行方法
        TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
        Teacher teacher = mapper.getTeacher(1);
        System.out.println(teacher);
        //关闭SqlSession
        sqlSession.close();
    }
    @Test
    public void getStudent() {
        //获取SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //执行方法
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        List<Student> studentList = mapper.getStudent();
        for (Student student : studentList) {
            System.out.println(student);
        }
        //关闭SqlSession
        sqlSession.close();
    }
    @Test
    public void getStudent2() {
        //获取SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //执行方法
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        List<Student> studentList = mapper.getStudent2();
        for (Student student : studentList) {
            System.out.println(student);
        }
        //关闭SqlSession
        sqlSession.close();
    }
}

一对多的处理

一个老师拥有多个学生

实体类

java 复制代码 
package com.findx.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Student {
    private int id;
    private String name;
    private int tid;
}
java 复制代码 
package com.findx.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.util.List;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Teacher {
    private int id;
    private String name;
    // 老师需要关联多个学生
    private List<Student> students;
}

按照查询或结果嵌套处理

java 复制代码 
package com.findx.dao;

import com.findx.pojo.Teacher;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface TeacherMapper {
    //获取所有的老师
    //List<Teacher> getTeacher();
    //获取指定老师下的所有学生及老师的信息
    Teacher getTeacherStudent(@Param("tid") int id);
    Teacher getTeacherStudent2(@Param("tid") int id);

}
xml 复制代码 
<?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">
<!--configuration核心配置文件-->
<mapper namespace="com.findx.dao.TeacherMapper">

<!--    <select id="getTeacher" resultType="Teacher">-->
<!--        select * from mybatis.teacher-->
<!--    </select>-->
    <!--按照结果来嵌套处理-->
    <select id="getTeacherStudent" resultMap="TeacherStudent">
        select s.id sid,s.name sname,t.name tname,t.id tid
        from student s,teacher t
        where s.tid = t.id and t.id = #{tid};
    </select>
    <resultMap id="TeacherStudent" type="Teacher">
        <id property="id" column="tid"/>
        <result property="name" column="tname"/>
        <collection property="students" ofType="Student">
            <id property="id" column="sid"/>
            <result property="name" column="sname"/>
            <result property="tid" column="tid"/>
        </collection>
    </resultMap>
    <!--按照查询来嵌套处理-->
    <select id="getTeacherStudent2" resultMap="TeacherStudent2">
        select * from mybatis.teacher where id=#{tid}
    </select>
    <resultMap id="TeacherStudent2" type="Teacher">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <collection property="students" column="id" javaType="ArrayList" ofType="Student" select="getStudent"></collection>
    </resultMap>
    <!--查询指定tid的全部学生-->
     <select id="getStudent" resultType="Student">
        select * from mybatis.student where tid=#{tid}
    </select>
</mapper>
java 复制代码 
package com.findx.dao;

import com.findx.pojo.Student;
import com.findx.pojo.Teacher;
import com.findx.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class MapperTest {
//    @Test
//    public void getTeacher() {
//        //获取SqlSession对象
//        SqlSession sqlSession = MybatisUtils.getSqlSession();
//        //执行方法
//        TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
//        List<Teacher> teachers = mapper.getTeacher();
//        for (Teacher teacher : teachers){
//            System.out.println(teacher);
//        }
//        //关闭SqlSession
//        sqlSession.close();
//    }
    @Test
    public void getTeacherStudent() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
        Teacher teacherStudent = mapper.getTeacherStudent2(1);
        System.out.println(teacherStudent);
        sqlSession.close();
    }
}

注意事项

复制代码 
JavaType和ofType都是用来指定对象类型的：
JavaType是用来指定pojo中属性的类型
ofType指定的是映射到list集合属性中pojo的类型。


关联-association
集合-collection

association是用于一对一和多对一 ，而collection是用于一对多的关系。

相关推荐
zzb158014 小时前
RAG from Scratch-优化-query
java·数据库·人工智能·后端·spring·mybatis
zzb15801 天前
RAG from Scratch-优化-routing
java·前端·网络·人工智能·后端·python·mybatis
MegaDataFlowers1 天前
使用注解开发
mybatis
常利兵1 天前
Spring Boot + MyBatis，给数据穿上“隐形盔甲”
java·spring boot·mybatis
Java程序之猿2 天前
SpringBoot + camel+IBM MQ实现消息队列处理
java·spring boot·mybatis
罗小爬EX2 天前
MyBatis Interceptor执行顺序详解（plugin机制、责任链模式）
mybatis·interceptor
weixin_704266052 天前
Spring整合MyBatis（一）
java·spring·mybatis
寻见9032 天前
10 分钟吃透 MyBatis 核心｜从底层原理到实战技巧，Java 开发者必藏（无废话干货）
java·mysql·mybatis
TTc_2 天前
对于子查询语句多条sql报错排查
数据库·sql·mybatis
热门推荐
01GitHub 镜像站点02Qwen3.5 开源全解析：从 0.8B 到 397B，代际升级 + 全场景选型指南03OpenClaw 使用和管理 MCP 完全指南04本地部署 OpenClaw + DeepSeek-R1 完全指南05OpenClaw macOS 完整安装与本地模型配置教程（实战版）06UV安装并设置国内源07Openclow安装保姆级教程08OpenClaw Control UI安全上下文访问配置09OpenClaw 飞书机器人不回复消息？3 小时踩坑总结10在 Windows 上配置 Claude Code从安装到解决网络问题