public class User{

private Card card_one;

private List<Card> card_many;

}

public class Card implements Serializable{
 private Integer id;
 private String code;
//省略set和get方法.
}

public class Person implements Serializable{
 private Integer id;
 private String name;
 private String sex;
 private Integer age;
 //人和身份證是一對(duì)一的關(guān)系
 private Card card;
//省略set/get方法.
}

package com.glj.mapper;

import com.glj.poji.Card;

public interface CardMapper {
 Card selectCardById(Integer id);
}

<?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.glj.mapper.CardMapper">
 <select id="selectCardById" parameterType="int" resultType="com.glj.poji.Card">
 select * from tb_card where id = #{id} 
 </select>
</mapper>

package com.glj.mapper;
 
import com.glj.poji.Person;
 
public interface PersonMapper {
 Person selectPersonById(Integer id);
}

<?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.glj.mapper.PersonMapper">
 <resultMap type="com.glj.poji.Person" id="personMapper">
 <id property="id" column="id"/>
 <result property="name" column="name"/>
 <result property="sex" column="sex"/>
 <result property="age" column="age"/>
 <association property="card" column="card_id" 
  select="com.glj.mapper.CardMapper.selectCardById"
  javaType="com.glj.poji.Card">
 </association>
 </resultMap>
 <select id="selectPersonById" parameterType="int" resultMap="personMapper">
 select * from tb_person where id = #{id}
 </select>
</mapper>

package com.glj.pojo;
 
import java.io.Serializable;
import java.util.List;
 
public class Clazz implements Serializable{
 private Integer id;
 private String code;
 private String name;
    //班級(jí)與學(xué)生是一對(duì)多的關(guān)系
 private List<Student> students;
//省略set/get方法
}

package com.glj.pojo;

import java.io.Serializable;

public class Student implements Serializable {
 private Integer id;
 private String name;
 private String sex;
 private Integer age;
    //學(xué)生與班級(jí)是多對(duì)一的關(guān)系
 private Clazz clazz;
//省略set/get方法
}

<?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.glj.mapper.ClazzMapper">
 <select id="selectClazzById" parameterType="int" resultMap="clazzResultMap">
 select * from tb_clazz where id = #{id}
 </select>
 <resultMap type="com.glj.pojo.Clazz" id="clazzResultMap">
 <id property="id" column="id"/>
 <result property="code" column="code"/>
 <result property="name" column="name"/>
 <!-- property: 指的是集合屬性的值, ofType：指的是集合中元素的類(lèi)型 -->
 <collection property="students" ofType="com.glj.pojo.Student"
 column="id" javaType="ArrayList"
 fetchType="lazy" select="com.glj.mapper.StudentMapper.selectStudentByClazzId">
  <id property="id" column="id"/>
  <result property="name" column="name"/>
  <result property="sex" column="sex"/>
  <result property="age" column="age"/>
 </collection>
 </resultMap>
</mapper>

package com.glj.mapper;

import com.glj.pojo.Clazz;

public interface ClazzMapper {
 Clazz selectClazzById(Integer id);
}

<?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.glj.mapper.StudentMapper">
 <select id="selectStudentById" parameterType="int" resultMap="studentResultMap">
 select * from tb_clazz c,tb_student s where c.id = s.id and s.id = #{id}
 </select>
 <select id="selectStudentByClazzId" parameterType="int" resultMap="studentResultMap">
 select * from tb_student where clazz_id = #{id}
 </select>
 <resultMap type="com.glj.pojo.Student" id="studentResultMap">
 <id property="id" column="id"/>
 <result property="name" column="name"/>
 <result property="sex" column="sex"/>
 <result property="age" column="age"/>
 <association property="clazz" javaType="com.glj.pojo.Clazz">
  <id property="id" column="id"/>
  <result property="code" column="code"/>
  <result property="name" column="name"/>
 </association>
 </resultMap>
</mapper>

package com.glj.mapper;

import com.glj.pojo.Student;

public interface StudentMapper {
 Student selectStudentById(Integer id); 
}