mybatis 一对一、一对多和多对多查询实例代码

  <select id="getClass" parameterType="int" resultMap="ClassesResultMap">  
    select * from class c,teacher t where c.teacher_id=t.t_id and c.c_id=#{id}  
  </select>  
  <resultMap type="com.lcb.user.Classes" id="ClassesResultMap">  
    <id property="id" column="c_id"/>  
    <result property="name" column="c_name"/>  
    <association property="teacher" javaType="com.lcb.user.Teacher">  
      <id property="id" column="t_id"/>  
      <result property="name" column="t_name"/>  
    </association>  
  </resultMap>  

<resultMap type="Teacher" id="teacherMaps">  
    <id column="id" property="id"/>  
    <result column="name" property="name"/>  
    <result column="class_name" property="className"/>  
    <collection property="students" ofType="Student" select="getStudents" column="id">  
    </collection>  
  </resultMap>  
  <!-- 查询所有的老师级各自的所有学生 -->  
  <select id="getAllTeacher" parameterType="Teacher" resultMap="teacherMaps">  
    SELECT  
      t.id,  
      t.NAME,  
      t.class_name  
    FROM  
      teacher t  
  </select>  
  <select id="getStudents" parameterType="int" resultType="Student">  
    select   
      s.id,  
      s. NAME,  
      s.class_name as className  
    from student s  
    where teacher_id = #{id}  
  </select> 

<select id="selectCountry" resultType="Country">  
  select cid,cname from country where cid=#{ooo}  
</select>  
<resultMap type="People" id="peopleMapper2">  
  <id column="pid" property="pid"/>  
  <result column="pname" property="pname"/>  
  <association property="country"   
         javaType="Country"  
         select="selectCountry"  
         column="countryId" />  
</resultMap>  
  <select id="selectById2" resultMap="peopleMapper2">  
  select pid,pname,countryId from people where pid = #{xxx}  
</select>