Mybatis的懒加载

╰半橙微兮° 2022-12-19 06:04 165阅读 0赞

## Mybatis的懒加载 ##

1.最近在最账单加载时用到了懒加载，记录一下

#### 1.mybatis提供了懒加载 ####

1.修改配置配置文件

##### 2.resultMap支持懒加载 #####

**association**

<resultMap id="BaseResultMapLazy" type="com.ls.po.ItemLazyVo" >
        <id column="id" property="id" jdbcType="BIGINT" />
        <result column="title" property="title" jdbcType="VARCHAR" />
        <result column="sell_point" property="sellPoint" jdbcType="VARCHAR" />
        <result column="price" property="price" jdbcType="DECIMAL" />
        <result column="num" property="num" jdbcType="INTEGER" />
        <result column="brand" property="brand" jdbcType="VARCHAR" />
        <result column="barcode" property="barcode" jdbcType="VARCHAR" />
        <result column="image" property="image" jdbcType="VARCHAR" />
        <result column="cid" property="cid" jdbcType="BIGINT" />
        <result column="status" property="status" jdbcType="TINYINT" />
        <result column="created" property="created" jdbcType="TIMESTAMP" />
        <result column="updated" property="updated" jdbcType="TIMESTAMP" />
        <association property="reptile" javaType="com.ls.po.Reptile" 
        select="com.ls.dao.ReptileDao.selectById" column="id">
        </association>
      </resultMap>
      <select id="findOrdersUserLazyLoading" resultMap="BaseResultMapLazy">
        select * from tb_item
      </select>

**collection**

<mapper namespace="com.ls.dao.ReptileDao">
    
      <select id="selectById" resultType="com.ls.po.Reptile">
        select  * from reptile where id=#{id}
      </select>
    </mapper>

3.然后写Dao，我这边就不写了  
**4.测试**

@Test
      public void queryListLazy(){ 
        List<ItemLazyVo> ordersUserLazyLoading = itemDao.findOrdersUserLazyLoading();
        //遍历上边的订单列表
        for(ItemLazyVo orders : ordersUserLazyLoading) { 
          //执行getUser()去查询用户信息，这里实现按需加载
          Reptile reptile = orders.getReptile();
          System.out.println(reptile);
        }
      }

结果  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMTk4MDA0_size_16_color_FFFFFF_t_70_pic_center]  
至此已实现懒加载  
详情请参加：  
https://mybatis.org/mybatis-3/zh/index.html  
https://mybatis.org/mybatis-3/zh/sqlmap-xml.html\#cache

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMTk4MDA0_size_16_color_FFFFFF_t_70_pic_center]: /images/20221120/25e825a4cdb648a78ad351ec3c32a087.png