mybatis：一对多

Posted 2022-03-29 小布丁value

mybatis： 一对多和多对一

多对一

1.搭建环境

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');

可以改动一下mybatis.config.xml
配置Teacher.xml



测试成功

2.查询一对多信息

问题：查找所有学生的信息以及学生对应的老师信息

按照嵌套查询处理

用resultType查不出来Teacher，怎么办呢？用resultMap

<resultMap id="StudentTeacher" type="Student">
        <result property="id" column="id"/>

        <result property="name" column="name"/>
        <association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
    </resultMap>
    <select id="getStudent" resultMap="StudentTeacher">
        select * from student
    </select>
    <select id="getTeacher" resultType="Teacher">
        select * from teacher where id=#id
    </select>

按照结果嵌套处理

<!--按照结果嵌套处理-->
    <select id="getStudent" resultMap="StudentTeacher2">
    select s.id  sid,s.name sname,t.name  tname, t.id tid from student s,teacher t where s.tid = t.id;
    </select>

    <resultMap id="StudentTeacher2" type="Student">
        <result property="id" column="sid"/>
        <result property="name" column="sname"/>
        <association property="teacher" javaType="Teacher">
            <result property="name" column="tname"/>
            <result property="id" column="tid"/>

        </association>
    </resultMap>