11 数据库表中列与实体类属性不一致的处理方式

张创琦 2022.03.13

  1. 创建 sql 表
  1. use ssm1;
  2. DROP TABLE IF EXISTS `users`;
  3. CREATE TABLE `users` (
  4. `user_id` int NOT NULL AUTO_INCREMENT COMMENT '用户id',
  5. `user_name` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL COMMENT '用户姓名',
  6. `user_age` int NULL DEFAULT NULL COMMENT '用户年龄', PRIMARY KEY (`user_id`) USING BTREE
  7. ) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_0900_ai_ci ROW_FORMAT = Dynamic;
  9. INSERT INTO `users` VALUES (1, '贾宝玉', 14); INSERT INTO `users` VALUES (2, '林黛玉', 13); INSERT INTO `users` VALUES (3, '薛宝钗', 15);
  11. SET FOREIGN_KEY_CHECKS = 1;
  1. 创建实体类
  1. package com.kkb.pojo;
  3. public class Users {
  5.     private Integer userId;
  6.     private String userName;
  7.     private Integer userAge;
  9.     @Override
  10.     public String toString() {
  11.         return "Users{" +
  12.                 "userId=" + userId +
  13.                 ", userName='" + userName + '\'' +
  14.                 ", userAge=" + userAge +
  15.                 '}';
  16.     }
  18.        // 省略 getter 和 setter 方法
  20. }
  1. 编写 UsersMapper.java 接口类
  1. package com.kkb.mapper;
  3. import com.kkb.pojo.Users;
  5. public interface UsersMapper {
  6.     // 1 使用列别名和resultType
  7.     Users queryByID(int userId);
  8.     // 2 使用resultMap
  9.     Users queryByID2(int userId);
  11. }
  1. 编写UsersMapper.xml 配置文件

路径在：com.kkb.test 下面

  1. <?xml version="1.0" encoding="UTF-8" ?>
  2. <!DOCTYPE mapper
  3.         PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  4. <mapper namespace="com.kkb.mapper.UsersMapper">
  5.     <!--方式1：resultType中的实体类的属性作为查询语句中的别名，让别名和属性保持一致-->
  6.     <select id="queryByID" resultType="com.kkb.pojo.Users">
  7.         select user_id as userId,user_name as userName,user_age as userAge from users where user_id=#{id};
  8.     </select>
  10.     <!--方式2：通过resultMap自行映射-->
  11.     <select id="queryByID2" resultMap="baseMap">
  12.         select * from users where user_id=#{id};
  13.     </select>
  14.     <resultMap id="baseMap" type="com.kkb.pojo.Users">
  15.         <id column="user_id" property="userId"/>
  16.         <result column="user_name" property="userName"/>
  17.         <result column="user_age" property="userAge"/>
  18.     </resultMap>
  19. </mapper>
  1. 在 mybatis.xml 中配置文件映射地址
  1. <!-- 注册映射文件 -->
  2.     <mappers>
  3.         <!-- 之前注册过的 -->
  4.         <mapper resource="com/kkb/mapper/UsersMapper.xml"></mapper>
  5.     </mappers>
  1. 编写测试类
  1. package com.kkb.test;
  3. import com.kkb.mapper.UsersMapper;
  4. import com.kkb.pojo.Users;
  5. import com.kkb.utils.MybatisUtil;
  6. import org.apache.ibatis.annotations.Mapper;
  7. import org.junit.Test;
  9. public class TestUsersMapper {
  10.     private UsersMapper usersMapper= MybatisUtil.getSqlSession().getMapper(UsersMapper.class);
  12.     // 测试成功
  13.     @Test
  14.     public void test01(){
  15.         Users user = usersMapper.queryByID(1);
  16.         System.out.println(user);
  17.     }
  19.     // 测试成功
  20.     @Test
  21.     public void test02(){
  22.         Users user = usersMapper.queryByID2(1);
  23.         System.out.println(user);
  24.     }
  25. }