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<Teacher> 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=绑定一个对应的Dao/Mapper接口-->
<mapper namespace="dao.TeacherMapper">

    <!--第一种-->
    <!--按结果嵌套查询-->
    <resultMap id="TS" type="Teacher">
        <result property="id" column="tid"/>
        <result property="name" column="tname"/>
        <!--一对多使用collection-->
        <!--集合使用ofType-->
        <collection property="student" ofType="Student">
            <result property="id" column="sid"/>
            <result property="name" column="sname"/>
            <result property="tid" column="tid"/>

        </collection>
    </resultMap>

    <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>
    <!--==================================================-->

    <resultMap id="TS2" type="Teacher">
        <collection property="student"  javaType="ArrayList" ofType="Student" select="getStudent" column="id">

        </collection>

    </resultMap>

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

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


</mapper>

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