MyBatis中的 One to One

1需求：根据id查询学生的身份证信息

学生实体Bean

public class Student {
    private Integer id;
    private String name;
    private Card card;  //关联的身份证对象

学生的Mapper（注意当学生类中包含其他类的bean对象时映射的写法！！ 学生类中包含了 Card对象）

<?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.cn.entity2.Student" >
    <resultMap id="studentMapper" type="com.cn.entity2.Student">
        <id property="id" column="id"></id>
        <result property="name" column="name"></result>      

        <association property="card" resultMap="com.cn.entity2.Card.cardMapper"></association>
    </resultMap>


    <select id="findByid" parameterType="int" resultMap="studentMapper">
        select s.id,s.name,c.cid,c.cunm
        from
        student s inner join cards c
        on s.scid = c.cid and s.id = #{id}
    </select>

</mapper>

身份证Bean

public class Card {
    private Integer cid;
    private String cunm;

身份证Mapper

<?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.cn.entity2.Card" >
    <resultMap id="cardMapper" type="com.cn.entity2.Card">
        <id property="cid" column="cid"></id>
        <result property="cunm" column="cunm"></result>
    </resultMap>
</mapper>