11.8-一对多多对一

一对多以及多对一:

package com.study.pojo;
import lombok.Data;
@Data
public class Student {
    private int id;
    private String name;
    private int tid;
}

package com.study.pojo;

import lombok.Data;

import java.util.List;

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

    //一对多
    List<Student> students;
}

• Xml配置

• <?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.study.dao.TeacherMapper">
     <select id="getStudent" resultMap="TeacherStudent">
         select t.id tid, t.name tname, s.id sid, s.name sname
        from student s join teacher t on s.tid = t.id and t.id = #{tid};
     </select>
  
    <resultMap id="TeacherStudent" type="Teacher">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <collection property="students" ofType="Student">
            <id property="id" column="sid"/>
            <result property="name" column="sname"/>
            <result property="tid" column="tid"/>
        </collection>
    </resultMap>
  </mapper>
  

Mysql引擎

InnoDB底层原理

索引

索引优化!