mybatis中的延迟加载

<!-- 延迟加载用户信息 -->

<resultMap type="Order" id="OrderUserMapLazy" autoMapping="true">

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

<!-- 对用户延迟加载 -->

<!-- select负责引用需要延迟加载的语句

用户表信息需要传入id 需要订单表负责传递

开启延迟加载

-->

<association property="user" javaType="User" select="queryUser"

column="user_id">

</association>

</resultMap>

<!-- 查询订单信息 -->

<select id="findOrderUserByNumberLazy" resultMap="OrderUserMapLazy">

select * from tb_order where order_number = #{number}

</select>

<!-- 延迟加载用户信息 -->

<select id="queryUser" resultType="User">

select * from tb_user where id=#{id}

</select>

1.在核心配置文件中开启延迟加载

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

2.出现CGLIB(缺少CGLIB依赖)

<dependency>

<groupId>cglib</groupId>

<artifactId>cglib</artifactId>

<version>3.1</version>

</dependency>

3.关闭延迟加载属性

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

延迟加载  一对一  一对多 多对多  例子

   <!-- 延迟加载用户信息 -->
  <resultMap type="Order" id="OrderUserMapLazy" autoMapping="true">
  <id column="id" property="id"/>
  <!-- 对用户延迟加载 -->
  <!-- select负责引用需要延迟加载的语句 
             用户表信息需要传入id   需要订单表负责传递
      开启延迟加载
  -->
  <association property="user" javaType="User" select="queryUser"
                                        column="user_id">
 
  </association>
  </resultMap>
  <!-- 查询订单信息 -->
  <select id="findOrderUserByNumberLazy" resultMap="OrderUserMapLazy">
     select * from tb_order where order_number = #{number}
  </select>
  <!-- 延迟加载用户信息 -->
  <select id="queryUser" resultType="User">
  select * from tb_user where id=#{id}
  </select>
 
  <!-- 一对多延迟加载订单详情 -->
  <resultMap type="Order" id="OrderUserDetailMapLazy" autoMapping="true">
     <id column="id" property="id"/>
     <!-- 延时加载用户信息 -->
  <association property="user" javaType="User" select="query_User"
  column="user_id">
  </association>
  <!-- 延时加载订单详情 订单详情的id和订单表中的id重复  所以起别名-->
  <collection property="orderdetail" javaType="List" ofType="Orderdetail" 
  select="query_Detail" column="detail_id">
  </collection>
  </resultMap>
  <!-- sql语句 -->
  <select id="findOrderUserDetailByNumberLazy" resultMap="OrderUserDetailMapLazy">
  select *,id as detail_id from tb_order where order_number = #{number}
  </select>
  <!-- queryUser -->
  <select id="query_User" resultType="User">
  select * from tb_user where id=#{id}
  </select>
  <!-- 延时加载订单详情 -->
  <select id="query_Detail" resultType="Orderdetail">
  select * from tb_orderdetail where id=#{id}
  </select>


  <!-- 多对多延迟加载 -->
  <!-- 定义订单的resultmap -->
  <resultMap type="Order" id="OrderUserDetailItemMapLazy1" autoMapping="true">
  <id column="id" property="id"/>
  <!-- 对用户信息进行延迟加载 -->
  <association property="user" javaType="User" select="query_User2"
  column="user_id">
  </association>
  <collection property="orderdetail" javaType="List" ofType="Orderdetail"
  select="query_Detail2" column="detail_id">
  </collection>
  </resultMap>
  <resultMap type="orderdetail" id=""></resultMap>
  <select id="findOrderUserDetailItemByNumberLazy" resultMap="OrderUserDetailItemMapLazy1">
  select *,id as detail_id from tb_order where order_number=#{number}
  </select>
  <!-- query_User2 -->
  <select id="query_User2" resultType="User">
  select * from tb_user where id=#{id}
  </select>
  <!-- query_Detail2 -->
  <select id="query_Detail2" parameterType="ItemMap1">
  select * from tb_orderdetail where id=#{id}
  </select>

1. 面试题：#和$符号的区别

1、#是预编译的方式，$是直接拼接；

2、#不需要关注数据类型，mybatis实现自动数据类型转换；$不做数据类型转换，需要自行判断数据类型；

3、#可以防止sql注入；$不能防止sql注入；

如果只有一个参数，默认情况下，#{}中可以写任意的名字；${}中只能用value来接收