一对多 一对多处理一个老师拥有多个学生（对老师而言，就是一对多的关系）1、新建实体类Teacherpackage com.sw.pojo; import lombok.Data; import java.io.Serializable; import java.util.List; /** * @Author suaxi * @Date 2020/12/13 10:55 */ @Data public class Teacher implements Serializable { private int id; private String name; //一个老师对应多个学生 private List<Student> students; } Studentpackage com.sw.pojo; import lombok.Data; import java.io.Serializable; /** * @Author suaxi * @Date 2020/12/13 10:55 */ @Data public class Student implements Serializable { private int id; private String name; private int tid; } 2、TeacherMapper.xml配置（两种方式）<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.sw.dao.TeacherMapper"> <!--按结果集嵌套处理--> <select id="findTeacherById" resultMap="TeacherStudent"> select s.id sid,s.name sname,t.id tid ,t.name tname from student s,teacher t where s.tid = t.id and t.id = #{tid}; </select> <resultMap id="TeacherStudent" type="teacher"> <result property="id" column="tid"/> <result property="name" column="tname"/> <!-- 集合使用 collection javaType="" 指定属性的类型 集合中的泛型信息，使用 ofType 获取 --> <collection property="students" ofType="Student"> <result property="id" column="sid"/> <result property="name" column="sname"/> <result property="tid" column="tid"/> </collection> </resultMap> <!--按照查询嵌套处理--> <select id="findTeacherById2" resultMap="TeacherStudent2"> select * from teacher where id = #{tid}; </select> <resultMap id="TeacherStudent2" type="Teacher"> <collection property="students" javaType="ArrayList" ofType="Student" select="findStudentByTeacherId" column="id"/> </resultMap> <select id="findStudentByTeacherId" resultType="Student"> select * from student where tid = #{tid}; </select> </mapper>注：1、关联 - association 【多对一】2、集合 - collection 【一对多】3、javaType & ofTypejavaType用来指定实体类中属性的类型ofType用来指定映射到List或者集合中的pojo类型，泛型中的约束类型