mybatis association與collection的區別

<resultMap type="cn.itcast.mybatis.po.Orders" id="OrdersUserResultMap">
        <!-- 配置映射的訂單信息 -->
        <id column="id" property="id" />
        <result column="user_id" property="userId" />
        <result column="number" property="number" />
        <result column="createtime" property="createTime" />
        <result column="note" property="note" />
        <!-- 配置關聯的用戶信息 -->

        <association property="user" javaType="cn.itcast.mybatis.po.User">
            <id column="user_id" property="id" />
            <result column="username" property="username" />
            <result column="sex" property="sex" />
            <result column="address" property="address" />
        </association>

    </resultMap>

    <resultMap type="cn.itcast.mybatis.po.Orders" id="OrdersAndOrdersDetail" extends="OrdersUserResultMap">

        

        <!-- 配置訂單詳細信息 一個訂單關聯查出了多條明細,要使用collection進行映射 collection:對關聯查到的多條記錄映射到集合對象中 
            property:將關聯查詢到多條記錄映射到對象的某個屬性中 ofType 指定映射集合屬性的的pojo對象的類型 -->
        <collection property="orderdetails" ofType="cn.itcast.mybatis.po.Orderdetail">
             <!-- id：訂單明細惟 一標識
             property:要將訂單明細的惟 一標識 映射到cn.itcast.mybatis.po.Orderdetail的哪一個屬性
               -->
             <id column="orderdetail_id" property="id"/>
             <result column="items_id" property="itemsId"/>
             <result column="items_num" property="itemsNum"/>
             <result column="orders_id" property="ordersId"/>
        
        </collection>

    </resultMap>