mybatis一对多

orders类（com.changez.sm.base.bean.Orders）主要属性：

	PRivate String id;	private String userId;	private String orderNum;	private Date createTime;	private String note;	private User user;	private Set<Ordertail> ordertails;
User类（com.changez.sm.base.bean.User）主要属性：
	private String id;	private String username;	private Date birthday;	private String sex;	private String address;
ordertail类（com.changez.sm.base.bean.Ordertail）主要属性：
	private int id;	private int orderId;	private int itemId;	private int itemNum;
一对多查询：
collection： 
property：bean中集合的属性名，
ofType：集合类型全限定名
select语句：其中的resultMap有以下两种选择： queryOrderAndDetailResultMapExtends或者queryOrderAndDetailResultMap
	<!-- 一对多查询 :查询订单及订单明细的信息 -->	<select id="queryOrderAndDetail" resultMap="queryOrderAndDetailResultMap">		SELECT 			tco.id ordersid, tco.user_id, tco.order_num, tco.create_time, 			tcd.id ordertailid, tcd.order_id, tcd.item_id, tcd.item_num, 			tcu.id userid, tcu.username, tcu.birthday, tcu.sex, tcu.address 		from 			temp_changez_orders tco, temp_changez_ordertail tcd, temp_changez_user tcu 		WHERE 			tco.id=tcd.order_id AND tco.user_id=tcu.id	</select>resultMap语句（方式一，将一对一， 一对多关系都写完整）：
<resultMap type="com.changez.sm.base.bean.Orders" id="queryOrderAndDetailResultMap">		<id column="ordersid" property="id"/>		<result column="user_id" property="userId"/>		<result column="order_num" property="orderNum"/>		<result column="create_time" property="createTime"/>		<result column="note" property="note"/>		<!-- 一对一的关系配置， 此处可以删掉，不影响一对多的配置  -->		<association property="user" javaType="com.changez.sm.base.bean.User">			<id column="userid" property="id"/>			<result column="username" property="username"/>			<result column="birthday" property="birthday"/>			<result column="address" property="address"/>			<result column="sex" property="sex"/>		</association>		<!-- 一对多的关系配置 -->		<collection property="ordertails" ofType="com.changez.sm.base.bean.Ordertail">			<id column="ordertailid" property="id"/>			<result column="order_id" property="orderId"/>			<result column="item_id" property="itemId"/>			<result column="item_num" property="itemNum"/>		</collection>	</resultMap>
resultMap语句（方式二，在一对一的关系中已经配置了orders和user的一对一关系， 可以使用extends关键字引用已有的对照关系）：
	<!-- 使用extends -->	<resultMap type="com.changez.sm.base.bean.Orders" id="queryOrderAndDetailResultMapExtends" extends="queryOrderAndUserResultMap">		<collection property="ordertails" ofType="com.changez.sm.base.bean.Ordertail">			<id column="ordertailid" property="id"/>			<result column="order_id" property="orderId"/>			<result column="item_id" property="itemId"/>			<result column="item_num" property="itemNum"/>		</collection>	</resultMap>orders和user的一对一关系配置：
	<resultMap type="com.changez.sm.base.bean.Orders" id="queryOrderAndUserResultMap">		<id column="ordersid" property="id"/>		<result column="user_id" property="userId"/>		<result column="order_num" property="orderNum"/>		<result column="create_time" property="createTime"/>		<result column="note" property="note"/>				<association property="user" javaType="com.changez.sm.base.bean.User">			<id column="userid" property="id"/>			<result column="username" property="username"/>			<result column="birthday" property="birthday"/>			<result column="address" property="address"/>			<result column="sex" property="sex"/>		</association>	</resultMap>