<resultMap type="Classes" id="classesMap">
    <id property="id" column="c_id" javaType="int"/>
    <result property="name" column="c_name" javaType="String"/>
<!--  <association property="teacher" javaType="Teacher" >
      <id property="id" column="t_id" javaType="int"/>
      <result property="name" column="t_name" javaType="String"/>
      <result property="age" column="t_age" javaType="int"/>
    </association> -->
    <association property="teacher" javaType="Teacher" resultMap="com.lsj.test.mybatis.mapper.TeacherMapper.teacherMap" ></association>
    <collection property="studentList" ofType="Student" resultMap="com.lsj.test.mybatis.mapper.StudentMapper.studentMap" ></collection>   
  </resultMap>
  <sql id="selectAllClassesSql">
    SELECT 
        c.id as c_id,c.name as c_name,teacher_id,
        t.id as t_id,t.name as t_name,t.age as t_age,
        s.id as stu_id,s.name as stu_name,s.classes_id 
    from classes c,teacher t,student s
  </sql>

 <resultMap type="Teacher" id="teacherMap">
    <id property="id" column="t_id" javaType="int"/>
    <result property="name" column="t_name" javaType="String"/>
    <result property="age" column="t_age" javaType="int"/> 
  </resultMap>