resultMap结果集映射

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resultMap结果集是用来定义sql查询的结果与java对象的映射关系。它主要解决2大问题：

1）可以解决POJO属性名和表结构的字段名不一致问题(甚至是不是标准的驼峰命名法)

2）可以完成高级查询，例如：一对一，一对多，多对多

其中还有一个比较重要的属性：autoMapping自动映射默认为true。

注意：1.如果true，并且列名称和字段名称一致，是可以完成映射。

2.如果为true，名称不一致，但是符合驼峰命名，但必须开启驼峰命名匹配。

下面简单介绍一个案列：

接口：UserMapper.java

package com.inter;

import java.util.List;

import org.apache.ibatis.annotations.Param;

import com.pojo.User;

public interface UserMapper {

//    查询数据

    public List<User> selectAll();

}

Mybatis配置文件：Mybatis-config.xml

<?xml version="1.0" encoding="UTF-8"?>

 <!DOCTYPE configuration

    PUBLIC "-//mybatis.org//DTD Config 3.0//EN"

    "http://mybatis.org/dtd/mybatis-3-config.dtd">

  <configuration>

      <!-- 加载外部配置文件 -->

      <properties resource="jdbc.properties"></properties>

      
/*

      <settings>

      <!--开启驼峰命名法-->

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

     </settings>

*/   
 

      <!-- 起别名 -->

     <typeAliases>

       <typeAlias alias="User" type="com.pojo.User"/>

     </typeAliases>

   <environments default="development">

     <environment id="development">

       <transactionManager type="JDBC"/>

       <dataSource type="POOLED">

         <property name="driver" value="${jdbc.driver}"/>

         <property name="url" value="${jdbc.url}"/>

         <property name="username" value="${jdbc.username}"/>

         <property name="password" value="${jdbc.password}"/>

       </dataSource>

     </environment>

   </environments>

   <!-- 指定mapper的配置文件 -->

   <mappers>

     <mapper resource="UserMapper.xml"/>

   </mappers>

 </configuration>

映射文件：UserMapper.xml

<?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.inter.UserMapper">

   <resultMap type="User" id="userResult" autoMapping="true">

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

   </resultMap>

   <!-- 查询所有的数据 -->

   <select id="selectAll" resultMap="userResult">

           select * from tb_user

   </select>

 </mapper>

实体类：User.java

package com.pojo;

public class User {

    private int id;

    private String name;

    private String age;

    private String sex;

    public int getId() {

        return id;

    }

    public void setId(int id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public String getAge() {

        return age;

    }

    public void setAge(String age) {

        this.age = age;

    }

    public String getSex() {

        return sex;

    }

    public void setSex(String sex) {

        this.sex = sex;

    }

    @Override

    public String toString() {

        return "User [id=" + id + ", name=" + name + ", age=" + age + ", sex=" + sex + "]";

    }

}

测试类：

package com.test;

import static org.junit.Assert.*;

import java.io.InputStream;

import java.util.List;

import org.apache.ibatis.io.Resources;

import org.apache.ibatis.session.SqlSession;

import org.apache.ibatis.session.SqlSessionFactory;

import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import org.junit.Before;

import org.junit.Test;

import com.inter.UserMapper;

import com.pojo.User;

public class TestMybatisoneTest {

     private UserMapper userMapper;

     InputStream inputStream;

     SqlSessionFactory sqlSessionFactory;

     SqlSession sqlSession;

    @Before

    public void setUp() throws Exception {

            String resource = "mybatis-config.xml";     

            inputStream = Resources.getResourceAsStream(resource);

            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

            sqlSession = sqlSessionFactory.openSession();

//            动态代理实现

            userMapper = sqlSession.getMapper(UserMapper.class);

    }

    @Test

    public void test4(){

        List<User> list = userMapper.selectAll();

        for (User user : list) {

            System.out.println(user+"   ");

        }

    }

}