Mybatis怎么实现ResultMap结果集

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Mybatis怎么实现ResultMap结果集

今天小编给大家分享一下Mybatis怎么实现ResultMap结果集的相关知识点，内容详细，逻辑清晰，相信大部分人都还太了解这方面的知识，所以分享这篇文章给大家参考一下，希望大家阅读完这篇文章后有所收获，下面我们一起来了解一下吧。

数据库中的字段

新建一个项目，拷贝之前的，测试实体类字段不一致的情况

1.新建一个mybatis-03

2.新建db.properties配置文件

driver=com.mysql.jdbc.Driverurl=jdbc:mysql://localhost:3306/mybatis?useSSL=false&useEncoding=false&characterEncoding=UTF-8&serverTimezone=GMTusername=rootpassword=root

3.新建mybatis-config.xml配置文件

<?xmlversion="1.0"encoding="UTF-8"?><!DOCTYPEconfigurationPUBLIC"-//mybatis.org//DTDConfig3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd"><configuration><propertiesresource="db.properties"/><environmentsdefault="development"><environmentid="development"><transactionManagertype="JDBC"/><dataSourcetype="POOLED"><propertyname="driver"value="${driver}"/><propertyname="url"value="${url}"/><propertyname="username"value="${username}"/><propertyname="password"value="${password}"/></dataSource></environment></environments><mappers><mapperresource="com/kuang/dao/UserMapper.xml"/></mappers></configuration>

4.创建com.kuang.utils包，包下创建MybatisUtils工具类

packagecom.kuang.utils;importorg.apache.ibatis.io.Resources;importorg.apache.ibatis.session.SqlSession;importorg.apache.ibatis.session.SqlSessionFactory;importorg.apache.ibatis.session.SqlSessionFactoryBuilder;importjava.io.IOException;importjava.io.InputStream;//sqlSessionFactory用来构建sqlSessionpublicclassMybatisUtils{//提升SqlSessionFactory的作用域privatestaticSqlSessionFactorysqlSessionFactory;static{try{//使用Mybatis第一步获取sqlSessionFactory对象Stringresource="mybatis-config.xml";//通过Resources读取配置文件InputStreaminputStream=Resources.getResourceAsStream(resource);//通过SqlSessionFactoryBuilder加载一个流，构建一个sqlSession工厂sqlSessionFactory=newSqlSessionFactoryBuilder().build(inputStream);}catch(IOExceptione){e.printStackTrace();}}//既然有了SqlSessionFactory，顾名思义，我们可以从中获得SqlSession的实例。//SqlSession提供了在数据库执行SQL命令所需的所有方法。publicstaticSqlSessiongetSqlSession(){returnsqlSessionFactory.openSession();}}

5.创建com.kuang.pojo包，里面存储实体类对象User

packagecom.kuang.pojo;publicclassUser{privateintid;privateStringname;privateStringpassword;publicUser(intid,Stringname,Stringpassword){this.id=id;this.name=name;this.password=password;}publicUser(){}publicintgetId(){returnid;}publicvoidsetId(intid){this.id=id;}publicStringgetName(){returnname;}publicvoidsetName(Stringname){this.name=name;}publicStringgetPassword(){returnpassword;}publicvoidsetPassword(Stringpassword){this.password=password;}@OverridepublicStringtoString(){return"User{"+"id="+id+",name='"+name+'\''+",password='"+password+'\''+'}';}}

6.创建com.kuang.dao包，里面存放接口UserMapper以及接口实现类UserMapper.xml

UserMapper

packagecom.kuang.dao;importcom.kuang.pojo.User;importjava.util.List;importjava.util.Map;publicinterfaceUserMapper{//根据用户id查询用户信息UsergetUserById(Integerid);}

UserMapper.xml

<?xmlversion="1.0"encoding="UTF8"?><!DOCTYPEmapperPUBLIC"-//mybatis.org//DTDMapper3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mappernamespace="com.kuang.dao.UserMapper"><selectid="getUserById"resultType="com.kuang.pojo.User"parameterType="Integer">select*fromuserwhereid=#{id}</select></mapper>

7.创建测试类

packagecom.kuang.dao;importcom.kuang.pojo.User;importcom.kuang.utils.MybatisUtils;importorg.apache.ibatis.session.SqlSession;importorg.junit.Test;importjava.util.HashMap;importjava.util.List;importjava.util.Map;publicclassUserDaoTest{@TestpublicvoidtestGetUserById(){//第一步：获取SqlSession对象SqlSessionsqlSession=MybatisUtils.getSqlSession();//执行Sql//方式一：getMapper（推荐使用）UserMapperuserDao=sqlSession.getMapper(UserMapper.class);Useruser1=userDao.getUserById(1);System.out.println(user1);//关闭sqlSessionsqlSession.close();}}

8测试结果及问题分析

8.1解决方案一：在sql查询语句中为pwd字段起别名起别名

将原sql语句

selectid,name,pwdaspasswordfromuserwhereid=#{id}

改为

selectid,name,pwdaspasswordfromuserwhereid=#{id}

8.2 resultMap 结果集映射

字段名：id name pwd
属性名：id name password

<resultMapid="UserMap"type="com.kuang.pojo.User"><resultcolumn="id"property="id"/><resultcolumn="name"property="name"/><resultcolumn="pwd"property="password"/></resultMap><selectid="getUserById"resultMap="UserMap">select*fromuserwhereid=#{id}</select>