<?xml version="1.0" encoding="utf8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.abc.mapper.StudentMapper">
<select id="getById" parameterType="int" resultMap="studentResultMap">
select s.id s_id,
s.name s_name,
s.gender s_gender,
s.major s_major,
s.grade s_grade,
t.id t_id,
t.name t_name,
t.gender t_gender,
t.title t_title,
t.research_area t_research_area
from student s left join teacher t
on s.supervisor_id = t.id
where s.id=#{id}
</select>
<resultMap id="studentResultMap" type="Student">
<id property="id" column="s_id"/>
<result property="name" column="s_name"/>
<result property="gender" column="s_gender"/>
<result property="major"  column="s_major"/>
<result property="grade"  column="s_grade"/>
<!--使用resultMap属性引用下面的教师实体映射-->
<association property="supervisor" javaType="Teacher"
resultMap="supervisorResultMap"/>
</resultMap>
<!--教师实体映射-->
<resultMap id="supervisorResultMap" type="Teacher">
<id property="id" column="t_id"/>
<result property="name" column="t_name"/>
<result property="gender" column="t_gender"/>
<result property="researchArea" column="t_research_area"/>
<result property="title" column="t_title"/>
</resultMap>
</mapper>

<?xml version="1.0" encoding="utf8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.abc.mapper.StudentMapper">
<select id="getById" parameterType="int" resultMap="studentResultMap">
select id,name,gender,major,grade,supervisor_id from student where id=#{id}
</select>
<select id="selectSupervisor" parameterType="int" resultMap="supervisorResultMap">
select id,name,gender,title,research_area
from teacher where id=#{id}
</select>
<resultMap id="studentResultMap" type="Student">
<id property="id" column="id"/>
<result property="name" column="name"/>
<result property="gender" column="gender"/>
<result property="major"  column="major"/>
<result property="grade"  column="grade"/>
<!--column="supervisor_id"不能少。此列的值作为参数
传递给要引用的select语句，用来查询相应学生的指导教师
的信息。select属性指定要引用的select语句-->
<association property="supervisor" javaType="Teacher"
column="supervisor_id" select="selectSupervisor"/>
</resultMap>
<!--教师实体映射-->
<resultMap id="supervisorResultMap" type="Teacher">
<id property="id" column="id"/>
<result property="name" column="name"/>
<result property="gender" column="gender"/>
<result property="researchArea" column="research_area"/>
<result property="title" column="title"/>
</resultMap>
</mapper>