十、resultMap 的关联方式实现多表查询(多对一)

<association>用于关联一个对象

•  property: 指定要关联的属性名
•  select: 设定要继续引用的查询, namespace+id
•  column: 查询时需要传递的列

 

<?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">
<mapper namespace="com.mapper.StudentMapper">
    <resultMap id="sMap" type="student">
        <id property="id" column="sid"/>
        <result property="name" column="sname"/>
        <result property="age" column="age"/>
        <result property="gender" column="gender"/>
        <result property="cid" column="cid"/>
        <association property="clazz" javaType="clazz">
            <id property="id" column="cid"/>
            <result property="name" column="cname"/>
            <result property="room" column="room"/>
        </association>
    </resultMap>
    <select id="selAll" resultMap="sMap">
        SELECT
        s.id sid,s.name sname,s.age,s.gender,c.id cid,c.name cname,c.room
        from t_student s
        LEFT JOIN t_class c
        on s.cid = c.id;
    </select>
</mapper>