mybatis联合查询遇到相同字段解决办法

「爱情、让人受尽委屈。」 2021-09-23 02:48 682阅读 0赞

# 问题 #

mybatis在联合查询的时候，有时候会遇到相同的字段，前面的字段值会覆盖后面字段的值。

<?xml version="1.0" encoding="UTF-8" ?>
    
    <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
    <mapper namespace="com.hand.core.demos.mapper.DemokeyMapper">
        <resultMap id="BaseResultMap" type="com.hand.core.demos.dto.Demokey">
            <result column="id" property="id" jdbcType="DECIMAL" />
            <result column="demo_id" property="demoId" jdbcType="DECIMAL" />
            <result column="name" property="name" jdbcType="VARCHAR" />
        </resultMap>
        
        <resultMap id="WithDemoResultMap" type="com.hand.core.demos.dto.Demokey">
            <result column="id" property="id" jdbcType="DECIMAL" />
            <result column="demo_id" property="demoId" jdbcType="DECIMAL" />
            <result column="name" property="name" jdbcType="VARCHAR" />
            <association property="demos" javaType="com.hand.core.demos.dto.Demos">
                <result column="id" property="id" jdbcType="DECIMAL" />
                <result column="name" property="name" jdbcType="VARCHAR" />
            </association>
        </resultMap>
        <sql id="WithDemos_Column_List">
            k.id,k.demo_id,k.name,d.id,d.name
        </sql>
        <select id="selectWithDemos" parameterType="com.hand.core.demos.dto.Demokey" resultMap="WithDemoResultMap">
            SELECT <include refid="WithDemos_Column_List"/>
            from hap_demokey k LEFT JOIN hap_demos d on k.demo_id = d.id
        </select>
        
    </mapper>

## 之前想的是会一一的映射 ##

## k.id,k.demo\_id,k.name,d.id,d.name 会映射 Demokey.id,Demokey.demo\_id,Demokey.name,Demos.id,Demos.name ##

## 但是实际却是这样的： ##

## Demokey.id,Demokey.demo\_id,Demokey.name,Demokey.id,Demokey.name ##

# 解决办法 #

<?xml version="1.0" encoding="UTF-8" ?>
    
    <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
    <mapper namespace="com.hand.core.demos.mapper.DemokeyMapper">
        <resultMap id="BaseResultMap" type="com.hand.core.demos.dto.Demokey">
            <result column="id" property="id" jdbcType="DECIMAL" />
            <result column="demo_id" property="demoId" jdbcType="DECIMAL" />
            <result column="name" property="name" jdbcType="VARCHAR" />
        </resultMap>
        
        <resultMap id="WithDemoResultMap" type="com.hand.core.demos.dto.Demokey">
            <result column="id" property="id" jdbcType="DECIMAL" />
            <result column="demo_id" property="demoId" jdbcType="DECIMAL" />
            <result column="name" property="name" jdbcType="VARCHAR" />
            <association property="demos" javaType="com.hand.core.demos.dto.Demos">
                <result column="did" property="id" jdbcType="DECIMAL" />
                <result column="dname" property="name" jdbcType="VARCHAR" />
            </association>
        </resultMap>
        <sql id="WithDemos_Column_List">
            k.id,k.demo_id,k.name,d.id did,d.name dname
        </sql>
        <select id="selectWithDemos" parameterType="com.hand.core.demos.dto.Demokey" resultMap="WithDemoResultMap">
            SELECT <include refid="WithDemos_Column_List"/>
            from hap_demokey k LEFT JOIN hap_demos d on k.demo_id = d.id
        </select>
        
    </mapper>

## 给对应的字段起别名，在映射的结果集对象里面用别名，就ok了。 ##