18 <!--
19 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
20 封装联表查询的数据(去除重复的数据)
21 select * from class c, teacher t where c.teacher_id=t.t_id and c.c_id=1
22 -->
23 <select id="getClass" parameterType="int" resultMap="ClassResultMap">
24 select * from class c, teacher t where c.teacher_id=t.t_id and c.c_id=#{id}
25 </select>
26 <!-- 使用resultMap映射实体类和字段之间的一一对应关系 -->
27 <resultMap type="me.gacl.domain.Classes" id="ClassResultMap">
28 <id property="id" column="c_id"/>
29 <result property="name" column="c_name"/>
30 <association property="teacher" javaType="me.gacl.domain.Teacher">
31 <id property="id" column="t_id"/>
32 <result property="name" column="t_name"/>
33 </association>
34 </resultMap>
35
36 <!--
37 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
38 SELECT * FROM class WHERE c_id=1;
39 SELECT * FROM teacher WHERE t_id=1 //1 是上一个查询得到的teacher_id的值
40 -->
41 <select id="getClass2" parameterType="int" resultMap="ClassResultMap2">
42 select * from class where c_id=#{id}
43 </select>
44 <!-- 使用resultMap映射实体类和字段之间的一一对应关系 -->
45 <resultMap type="me.gacl.domain.Classes" id="ClassResultMap2">
46 <id property="id" column="c_id"/>
47 <result property="name" column="c_name"/>
48 <association property="teacher" column="teacher_id" select="getTeacher"/>
49 </resultMap>
50
51 <select id="getTeacher" parameterType="int" resultType="me.gacl.domain.Teacher">
52 SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id}
53 </select>
