mybatis一对多的配置

基本配置与onetoone的类似，不同的是一对多用到了两个新的标签

下面是一个一对多的例子：

<!--方式一: 嵌套结果: 使用嵌套结果映射来处理重复的联合结果的子集
SELECT * FROM class c, teacher t,student s WHERE c.teacher_id=t.t_id AND c.C_id=s.class_id AND  c.c_id=1
-->
<select id="getClass3" parameterType="int" resultMap="ClassResultMap3">
select  *  from  class  c,  teacher  t,student  s  where  c.teacher_id=t.t_id  and  c.C_id=s.class_id  and
c.c_id=#{id}
</select>
<resultMap type="_Classes" id="ClassResultMap3">
<id property="id" column="c_id"/>
<result property="name" column="c_name"/>
<association property="teacher" column="teacher_id" javaType="_Teacher">
<id property="id" column="t_id"/>
<result property="name" column="t_name"/>
</association>
<!-- ofType 指定 students 集合中的对象类型 -->
<collection property="students" ofType="_Student">
<id property="id" column="s_id"/>
<result property="name" column="s_name"/>
</collection>
</resultMap>
<!--方式二：嵌套查询：通过执行另外一个 SQL 映射语句来返回预期的复杂类型
SELECT * FROM class WHERE c_id=1;
SELECT * FROM teacher WHERE t_id=1  //1 是上一个查询得到的 teacher_id 的值
SELECT * FROM student WHERE class_id=1  //1 是第一个查询得到的 c_id 字段的值
-->
<select id="getClass4" parameterType="int" resultMap="ClassResultMap4">
select * from class where c_id=#{id}
</select>
<resultMap type="_Classes" id="ClassResultMap4">
<id property="id" column="c_id"/>
<result property="name" column="c_name"/>
<association  property="teacher"  column="teacher_id"  javaType="_Teacher"
select="getTeacher2"></association>
<collection property="students" ofType="_Student" column="c_id" select="getStudent"></collection>
</resultMap>
<select id="getTeacher2" parameterType="int" resultType="_Teacher">
SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id}
</select>
<select id="getStudent" parameterType="int" resultType="_Student">
SELECT s_id id, s_name name FROM student WHERE class_id=#{id}
</select>

sql映射文件一定要记得到conf.xml中注册，有设置别名的记得到到conf.xml里设置