mybatis使用resultMap获取不到值的解决方案

目录

• mybatis resultMap获取不到值
• 问题描述
• 原因及解决方法
• Mybatis 从数据库中获取值为null ResultMap
• 要解决的问题：属性名和字段名不一致
• 解决方法

mybatis resultMap获取不到值

    <resultMap type="com.fc.model.Shop" id="employeeMap">
        <id column="shop_id" property="shopId"></id>
        <result column="name" property="name"></result>
    </resultMap> 
 
    <!-- 获取店员列表 -->
    <select id="getEmployeeList" parameterType="java.util.Map" resultMap="employeeMap">
    	select *, (  
		    6371 * acos (  
		      cos ( radians( #{latitude} ) )  
		      * cos( radians( s.latitude ) )  
		      * cos( radians( s.longitude ) - radians( #{longitude} ) )  
		      + sin ( radians( #{latitude} ) )  
		      * sin( radians( s.latitude ) )  
		    )  
		) as distance
    	from
    	<include refid="table_name"></include> as e
    	join <include refid="table_name_shop"></include> as s
    	on e.shop_id = s.shop_id
    	limit #{offset, jdbcType=INTEGER}, #{limit, jdbcType=INTEGER}
    </select>

问题描述

前端获取的接口没有得到distance字段

原因及解决方法

在实体中没有声明distance字段，在实体中声明

Mybatis 从数据库中获取值为null ResultMap

ResultMap和返回值为空的的问题

要解决的问题：属性名和字段名不一致

代码块如下：

接口：

package com.lx.dao;
import com.lx.pojo.User;
public interface UserMapper {
    User getUserById(int id);
}

穿插：

要想使用@Alias注解的话,必须要在mybatis-config.xml配置typeAlias,例如:

<typeAliases>
     <package name="com.lx.pojo"/>
</typeAliases>

实体类：

package com.lx.pojo;
import org.apache.ibatis.type.Alias;
@Alias("user")
public class User {
    private int id;
    private String name;
    private String pwd;
    public User() {
    }
    public User(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }
    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 getPwd() {
        return pwd;
    }
    public void setPwd(String pwd) {
        this.pwd = pwd;
    }
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", pwd='" + pwd + '\'' +
                '}';
    }
}

resouce目录下的数据库配置文件：

driver=com.Mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis?useSSL=false&useUnicode=true&characterEncoding=UTF-8
username=root
pwd=123456

<?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>
    <properties resource="db.properties" />
<!--    可以给实体类起别名-->
  <typeAliases>
        <package name="com.lx.pojo"/>
    </typeAliases>
   <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="passWord" value="${pwd}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com\lx\dao\UserMapper.xml"/>
    </mappers>
</configuration>

工具类：获取sqlSession

package com.lx.utils;
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 java.io.IOException;
import java.io.InputStream;
public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;
    static{
        //使用Mybatis第一步：获取sqlSessionFactory对象
        String resource = "mybatis-config.xml";
        InputStream inputStream = null;
        try {
            inputStream = Resources.getResourceAsStream(resource);
        } catch (IOException e) {
            e.printStackTrace();
        }
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    }
    //有了SqlSessionFactory ,可以从中获取SqlSession 的实例
    //SqlSession 在其中包含了面向数据库执行 SQL 命令的所有方法
    public static SqlSession getSqlSession(){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        return sqlSession;
    }
}

执行sql语句，帮定UserMapper接口的xml配置文件：

<?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">
<!--namespace=绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.lx.dao.UserMapper">
  <select id="getUserById" parameterType="int" resultType="user">
      select * from user where id= #{id}
  </select>
</mapper>

测试类：

import com.lx.dao.UserMapper;
import com.lx.pojo.User;
import com.lx.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
public class test3 {
    @Test
    public void userbyid(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = mapper.getUserById(1);
        System.out.println(user);
        sqlSession.close();
    }
}

测试结果：

pwd的值为null

mybatis会根据这些查询的列名(会将列名转化为小写,数据库不区分大小写) , 去对应的实体类中查找相应列名的set方法设值 , 由于找不到setPassword() , 所以pwd返回null ; 【自动映射】

解决方法

使用结果集映射:ResultMap

column是数据库表的列名 , property是对应实体类的属性名

<?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">
<!--namespace=绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.lx.dao.UserMapper">
<resultMap id="usermap" type="user">
    <!-- id为主键 -->
    <id column="id" property="id"/>
    <!-- column是数据库表的列名 , property是对应实体类的属性名 -->
    <result column="name" property="name"/>
    <result column="password" property="pwd"/>
</resultMap>
    <select id="getUserById" resultMap="usermap">
        select * from user where id=#{id}
    </select>
<!--  <select id="getUserById" parameterType="int" resultType="user">-->
<!--      select * from user where id= #{id}-->
<!--  </select>-->
</mapper>

测试结果：

以上为个人经验，希望能给大家一个参考，也希望大家多多支持编程界。