一对一和一对多

Mahe666

一对一

<?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.mahe666.mapper.StudentMapper">

    <!--
        思路
        1，查询所有的学生
        2，根据查询出来的学生的tid，寻找对应的老师
            因为resultType查不出来想要的teacher
            所以给这个返回的东西做点手脚，给它变为resultMap
    -->

    <select id="getStudent" resultMap="StudentAndTeacherMap">
        select * from student
    </select>

    <resultMap id="StudentAndTeacherMap" type="student">
        <result property="id" column="id"/>
        <result property="name" column="name"/>
        <!--复杂的属性我们需要单独处理-->
        <!--
            如果是个对象，我们需要使用association
            如果是个集合，我们需要使用collection
            <association property=""/>
            <collection property=""/>
        -->

        <!--property是返回类型的属性，javaType是对应的实体类-->
        <association property="teacher" column="tid" javaType="teacher" select="getTeacherByTid"/>

    </resultMap>

    <select id="getTeacherByTid" resultType="teacher">
        select * from teacher where id = #{tid}
    </select>

</mapper>

一对多

<?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.mahe666.mapper.TeacherMapper">

    <!--子查询的方式-->
    <select id="getTeacher2" resultMap="teacherAndStudentMap2">
        select * from teacher
    </select>
    <resultMap id="teacherAndStudentMap2" type="teacher">
        <result property="id" column="id"/>
        <result property="name" column="name"/>

        <collection property="studentList" column="id" javaType="ArrayList" ofType="student" select="getStudentByTid"/>
    </resultMap>

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


</mapper>

多参数传递

column="{参数名1 = 列名1},{参数名2 = 列名2}"