1.一对一关联查询（在ordermapper.xml中配置）：
<resultMap type="order" id="order_user_map">
<!-- <id>用于映射主键 -->
<id property="id" column="id"/>
<!-- 普通字段用result映射 -->
<result property="userId" column="user_id"/>
<result property="number" column="number"/>
<result property="createtime" column="createtime"/>
<result property="note" column="note"/>
<!-- aociation用于配置一对一关系
property:order里面的user属性
JAVAtYPE:user的数据类型，支持别名
-->
<association property="User" javaType="com.itheima.mybatis.pojo.User">
<id property="id" column="user_id"/>
<!-- 普通字段用result映射 -->
<result property="username" column="username"/>
<result property="address" column="address"/>
<result property="birthday" column="birthday"/>
<result property="sex" column="sex"/>
</association>
</resultMap>
<select id="getOrderUserMap" resultMap="order_user_map">
select
o.`id`,
o.`user_id` userId,
o.`number`,
o.`createtime`,
o.`note`,
u.username,
u.address,
u.birthday,
u.sex
from `order` o
left join user u
on u.id=o.user_id
</select>
2.一对多关联查询
<resultMap type="com.itheima.mybatis.pojo.User" id="user_order_map">
<!-- <id>用于映射主键 -->
<id property="id" column="id"/>
<!-- 普通字段用result映射 -->
<result property="username" column="username"/>
<result property="address" column="address"/>
<result property="birthday" column="birthday"/>
<result property="sex" column="sex"/>
<!-- collection用于对应一对多关联
property：user中order的属性
oftype：order的数据类型 支持别名
-->
<collection property="orders" ofType="com.itheima.mybatis.pojo.Order">
<id property="id" column="oid"/>
<result property="number" column="number"/>
<result property="createtime" column="createtime"/>
<result property="note" column="note"/>
</collection>
</resultMap>
<select id="getUserOrderMap" resultMap="user_order_map">
select
o.`id` oid,
o.`user_id` userId,
o.`number`,
o.`createtime`,
o.`note`,
u.username,
u.address,
u.birthday,
u.sex
from `user` u
left join `order` o
on u.id=o.user_id
</select>