mybatis教程之延遲加載詳解

<!-- 全局配置參數(shù) --> 
 
<settings> 
 
<!-- 延遲加載總開(kāi)關(guān) --> 
 
<setting name="lazyLoadingEnabled" value="true" /> 
 
<!-- 設(shè)置按需加載 --> 
 
<setting name="aggressiveLazyLoading" value="false" /> 
 
</settings> 

<!-- 一對(duì)一查詢(xún)延遲加載 
   開(kāi)始只查詢(xún)訂單，對(duì)用戶(hù)信息進(jìn)行延遲加載  
   --> 
   <select id="findOrderUserListLazyLoading" resultMap="orderCustomLazyLoading"> 
     SELECT  
     orders.* 
    FROM 
     orders 
   </select> 

<!-- 一對(duì)一查詢(xún)延遲加載 的配置 --> 
  <resultMap type="orders" id="orderCustomLazyLoading"> 
    <!-- 完成了訂單信息的映射配置 --> 
    <!-- id：訂單關(guān)聯(lián)用戶(hù)查詢(xún)的唯 一 標(biāo)識(shí) --> 
    <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" /> 
    <!-- 配置用戶(hù)信息的延遲加載 select：延遲加載執(zhí)行的sql所在的statement的id，如果不在同一個(gè)namespace需要加namespace  
      sql：根據(jù)用戶(hù)id查詢(xún)用戶(hù)信息 column：關(guān)聯(lián)查詢(xún)的列 property:將關(guān)聯(lián)查詢(xún)的用戶(hù)信息設(shè)置到Orders的哪個(gè)屬性 --> 
    <association property="user" 
      select="com.sihai.mybatis.mapper.UserMapper.findUserById" column="user_id"></association> 
 
 
  </resultMap> 

//一對(duì)一查詢(xún)，延遲加載 
  public List<Orders> findOrderUserListLazyLoading() throws Exception; 

// 一對(duì)一查詢(xún)延遲加載 
  @Test 
  public void testFindOrderUserListLazyLoading() throws Exception { 
 
    SqlSession sqlSession = sqlSessionFactory.openSession(); 
    // 創(chuàng)建mapper代理對(duì)象 
    OrdersMapperCustom ordersMapperCustom = sqlSession 
        .getMapper(OrdersMapperCustom.class); 
 
    // 調(diào)用方法 
    List<Orders> list = ordersMapperCustom.findOrderUserListLazyLoading(); 
     
    //這里執(zhí)行延遲加載，要發(fā)出sql 
    User user = list.get(0).getUser(); 
    System.out.println(user); 
     
  }