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;//班级与学生是一对多的关系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;//学生与班级是多对一的关系private Clazz clazz;
//省略set/get方法
}

package com.glj.mapper;import com.glj.pojo.Clazz;public interface ClazzMapper {Clazz selectClazzById(Integer id);
}

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapperPUBLIC "-//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: 指的是集合属性的值, ofType：指的是集合中元素的类型 --><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.Student;public interface StudentMapper {Student selectStudentById(Integer id);
}

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapperPUBLIC "-//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>