mybatis使用resultMap获取不到值的解决方案_Java教程

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使用resultMap获取不到值的解决方案

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：

mybatis使用resultMap获取不到值的解决方案

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】

mybatis使用resultMap获取不到值的解决方案

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：

mybatis使用resultMap获取不到值的解决方案