警惕Mybatis的Foreach的的副作用

来源：互联网发布：apache maven怎么安装编辑：程序博客网时间：2024/05/05 03:38

对于如下SQL：
假设有如下的mapper:

<select id=”testForeach”  parameterType=”map”  resultType=”Student”>    Select * from student    <where>     <choose>        <when test=”ID != null and ID != ‘’ ”>            ID = #{ID}        </when>        <when test=” IDArr != null and IDArr.size()>0”>            And ID IN            <foreach collection="IDArr" open="("                separator="," close=")" item="ID">                ${ID}            </foreach>        </when></choose></where>

当我们传入的IDArr时，最后产生的SQL为：
Select * from student where ID = ‘998’ AND ID IN ( ‘123’, ’234’,…..,’998’)
解决办法：
解决办法有
1）将红色的ID 换成别的名称，比如“item”。
2）这两个if 是对同一个字段判断，改为choose… when 结构

<select id=”testForeach”  parameterType=”map”  resultType=”Student”>    Select * from student    <where>     <choose>        <when test=”ID != null and ID != ‘’ ”>            ID = #{ID}        </when>        <when test=” IDArr != null and IDArr.size()>0”>            And ID IN            <foreach collection="IDArr" open="("                separator="," close=")" item="ID">                ${ID}            </foreach>        </when></choose></where>

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