mybatis知识点

一对一映射

<mapper namespace="cn.itcast.mybatis.mapper.OrdersMapper">
	<!-- 根据id查询用户 -->
	<resultMap type="orders" id="orders">
		<result column="id" property="id"/>
		<result column="user_id" property="userId"/>
		<result column="number" property="number"/>
		<collection property="user" javaType="user">
				<result column="user_id" property="id"/>
				<result column="username" property="username" />
		</collection>
	</resultMap>
	
	<select id="findOrersByUser"
		resultMap="orders">
		select 
			o.id,o.user_id,o.number,u.username
		 from orders o left join user u on u.id=o.user_id
	</select>
</mapper>

List<Orders> findOrersByUser();

一对多

	<resultMap type="user" id="user">
		<result column="id" property="id"/>
		<result column="username" property="username"/>
		<result column="birthday" property="birthday"/>
		<result column="sex" property="sex"/>
		<result column="address" property="address"/>
		<collection property="ordersList" ofType="orders">
			<result column="oid" property="id"/>
			<result column="number" property="number"/>
		</collection>
	</resultMap>
	<!-- 根据id查询用户 	o.id,o.user_id,o.number,.o.createtime,u.username,u.address,u.sex,u.birthday-->
	<select id="findUserByOrders" resultMap="user">
		select 
			u.id,u.username,u.birthday,u.sex,u.address,o.id "oid", o.number
		 from user u  left join orders o on o.user_id = u.id
	</select>

List<User> findUserByOrders();