mybatis 关联映射

<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >

<mapper>

    <resultMap id="studentResultMap" type="com.demo.domain.Student">

        <id property="id" column="id"/>

        <result property="name" column="name"/>

        <result property="sex" column="sex"/>

        <result property="age" column="age"/>

        <!-- 关联映射：一个学生关联一个班级 -->

        <association property="clazz" column="clazz_id" javaType="com.demo.domain.Clazz" select="selectClazzWithId"/>

    </resultMap>

    <!-- 查询关联班级 -->

    <select id="selectClazzWithId" resultType="com.demo.domain.Clazz">

        SELECT * FROM TB_CLAZZ WHERE id = #{id}

    </select>

    <!-- 查询学生 -->

    <select id="selectStudent" resultMap="studentResultMap">

        SELECT * FROM TB_STUDENT

    </select>

</mapper>

<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >

<mapper>

    <resultMap id="clazzResultMap" type="com.demo.domain.Clazz">

        <id property="id" column="id"/>

        <result property="code" column="code"/>

        <!-- 关联映射：一个班级有多个学生，返回一个 List 集合 -->

        <collection property="students" javaType="ArrayList" column="id" ofType="com.demo.domain.Student" select="selectStudentWithId"/>

    </resultMap>

    <!-- 查询关联的学生 -->

    <select id="selectStudentWithId" resultType="com.demo.domain.Student">

        SELECT * FROM TB_STUDENT WHERE clazz_id = #{id}

    </select>

    <!-- 查询班级 -->

    <select id="selectClazz" resultMap="clazzResultMap">

        SELECT * FROM TB_CLAZZ

    </select>

</mapper>