多对一数据查询
<!-- select s.id, s.name, s.tid, t.name as tname from student as s, Teacher as t where s.tid = t.id;-->
<!-- 方式一，按查询嵌套查询-->
<resultMap id="StudentTeacher1" type="Student">
<association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
</resultMap>
<select id="getStudent" resultMap="StudentTeacher1">
select * from student
</select>
<select id="getTeacher" resultType="Teacher">
select * from teacher where id = #{tid}
</select>
<!-- 方式二：按结果嵌套查询-->
<select id="getStudent2" resultMap="StudentTeacher2">
select s.id sid, s.name sname, s.tid tid, t.name tname
from student s, teacher t
where s.tid = t.id
order by sid asc
</select>
<resultMap id="StudentTeacher2" type="Student">
<id property="id" column="sid"/>
<result property="name" column="sname"/>
<association property="teacher" column="tid" javaType="Teacher">
<result property="id" column="tid"/>
<result property="name" column="tname"/>
</association>
</resultMap>
一堆多数据查询
<select id="getTeacherById" resultMap="TeacherStudent">
select t.id tid, t.name tname, s.id sid, s.name sname
from Student s, Teacher t
where t.id = s.tid
and t.id = #{id}
</select>
<resultMap id="TeacherStudent" type="Teacher">
<result property="id" column="tid"/>
<result property="name" column="tname"/>
<collection property="students" ofType="Student">
<result property="id" column="sid"/>
<result property="name" column="sname"/>
<result property="tid" column="tid"/>
</collection>
</resultMap>
<!-- ===================-->
<resultMap id="TeacherStudent1" type="Teacher">
<result property="id" column="id"/>
<result property="name" column="name"/>
<collection property="students" javaType="ArrayList" ofType="Student" select="getStudent" column="id"/>
</resultMap>
<select id="getTeacherById1" resultMap="TeacherStudent1">
select * from teacher t where id = #{id}
</select>
<select id="getStudent" resultType="Student">
select * from student where tid = #{tid}
</select>
