使用mybatis的延遲載入，需要兩個步驟：

1.在全域性配置檔案中新增一下語句（lazyLoadingEnabled預設為false，aggressiveLazyLoading預設為true）

<settings>

    <!-- 延遲載入總開關 -->

    <setting name="lazyLoadingEnabled" value="true"/>

    <!-- 侵入式延遲 -->

    <setting name="aggressiveLazyLoading" value="false"/>

</settings>

2.寫好對映檔案

<resultMap type="User" id="CacheTest">

    <id column="id" property="id" />

    <result column="username" property="username" />

    <result column="birthday" property="birthday" />

    <result column="address" property="address" />

    <!-- column相當於傳入parameter  ofType相當於resultType -->

    <collection property="orderList" column="id" ofType="Order"

        select="resultMap.resultMapMapper.CacheTestSelect">

        <result column="number" property="number" />

        <result column="createtime" property="createtime" />

    </collection>

</resultMap>

<select id="CacheTest" resultMap="CacheTest">

    select * from user

</select>

<select id="CacheTestSelect" parameterType="int" resultType="Order">

    select * from orders where user_id = #{id}

</select>

這樣查詢一開始會執行select * from user

然後當讀取到orderList時才會執行select * from orders where user_id = #{id}