mybatis一对多操作数据库

TeacherMapper.java

package dao;

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

import java.util.List;

public interface    TeacherMapper {

    //test环境
//    public List getTeacher();

    //获取指定老师下的学生

    public Teacher getTeacher(@Param("tid") int id);


    public Teacher getTeacher2(@Param("tid") int id);
}

TeacherMapper.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">

namespace="dao.TeacherMapper">

    
    
    "TS" type="Teacher">
        "id" column="tid"/>
        "name" column="tname"/>
        
        
        "student" ofType="Student">
            "id" column="sid"/>
            "name" column="sname"/>
            "tid" column="tid"/>

        
    

    <select id="getTeacher" resultMap="TS">
        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>
    

    "TS2" type="Teacher">
        "student"  javaType="ArrayList" ofType="Student" select="getStudent" column="id">

        

    

    <select id="getTeacher2" resultMap="TS2">
        select * from teacher where id = #{tid}

    select>
    <select id="getStudent" resultType="Student">
        select * from  student where tid = #{id}
    select>

MyTset.java

package dao;

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

import java.util.List;

public class MyTest {
    @Test
    public void getTeacher()
    {
        SqlSession sqlSession= MybatisUtils.getSqlSession();
        TeacherMapper teacherMapper=sqlSession.getMapper(TeacherMapper.class);
        Teacher teacher=teacherMapper.getTeacher(1);
        System.out.println(teacher);
        sqlSession.close();
    }
    @Test
    public void getTeacher2()
    {
        SqlSession sqlSession= MybatisUtils.getSqlSession();
        TeacherMapper teacherMapper=sqlSession.getMapper(TeacherMapper.class);
        Teacher teacher=teacherMapper.getTeacher2(1);
        System.out.println(teacher);
        sqlSession.close();
    }
}

今天的第一种和昨天的第二种是同一类型的查询方式，个人比较喜欢第二种，喜欢SQL语句复杂一些，而不是套娃复杂一些