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【原】后端技术：mybatis中resultMap用法示例笔记

 IT技术分享社区 2022-10-20 发布于江苏

1、概念

resultMap属于mybatis返回操作结果的一个标签，可以用来映射select查询出来结果的集合，主要作用是将实体类中的字段与数据库表中的字段进行关联映射。并且支持复杂的返回结果类型。

2、使用场景

2.1 属性映射

当数据库字段和项目中的实体属性不一致时，可以使resultMap进行数据库字段和实体类属性的映射关系
比如：
     column="id" jdbcType="integer" property="id" />         column="user_name" jdbcType="VARCHAR" property="userName" />

说明：如果数据库字段和实体类属性一致的情况下，可以省略不写。

2.2 实现Java复杂实体类用法

a.初始化脚本


DROP TABLE IF EXISTS `t_user`;CREATE TABLE `t_user` (  `id` int(11) NOT NULL AUTO_INCREMENT,  `user_name` varchar(255) CHARACTER SET armscii8 DEFAULT NULL,  `password` varchar(255) CHARACTER SET armscii8 DEFAULT NULL,  `last_login_time` datetime DEFAULT NULL,  `sex` tinyint(4) DEFAULT NULL,  PRIMARY KEY (`id`)) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8;

-- ------------------------------ Records of t_user-- ----------------------------INSERT INTO `t_user` VALUES ('1', 'xiaoxin', '123', '2019-07-27 16:01:21', '1');INSERT INTO `t_user` VALUES ('2', 'jack jo', '123', '2019-07-24 16:01:37', '1');INSERT INTO `t_user` VALUES ('4', 'landengdeng', '123', '2019-07-24 16:01:37', '1');INSERT INTO `t_user` VALUES ('5', 'max', '123', '2019-07-24 16:01:37', '1');INSERT INTO `t_user` VALUES ('6', 'liua11', '123456', null, '1');INSERT INTO `t_user` VALUES ('7', 'xiaozhang', '888888', null, '1');DROP TABLE IF EXISTS `t_hobby`;CREATE TABLE `t_hobby` (  `id` int(11) NOT NULL,  `hobbyName` varchar(50) CHARACTER SET utf8 DEFAULT NULL,  `userId` int(11) DEFAULT NULL,  PRIMARY KEY (`id`)) ENGINE=InnoDB DEFAULT CHARSET=latin1;

-- ------------------------------ Records of t_hobby-- ----------------------------INSERT INTO `t_hobby` VALUES ('0', '音乐', '2');INSERT INTO `t_hobby` VALUES ('1', '篮球', '1');INSERT INTO `t_hobby` VALUES ('2', '读书', '1');

b.定义实体类

定义实体 UserDO.java

public class UserDO {private Integer id;private String userName;private String password;private Integer sex;private Date lastLoginTime;

public Integer getId() {return id;    }

public void setId(Integer id) {this.id = id;    }

public String getUserName() {return userName;    }

public void setUserName(String userName) {this.userName = userName;    }

public String getPassword() {return password;    }

public void setPassword(String password) {this.password = password;    }

public Integer getSex() {return sex;    }

public void setSex(Integer sex) {this.sex = sex;    }

public Date getLastLoginTime() {return lastLoginTime;    }

public void setLastLoginTime(Date lastLoginTime) {this.lastLoginTime = lastLoginTime;    }

@Override    public String toString() {return "UserDO{" +"id=" + id +", userName='" + userName + '\'' +", password='" + password + '\'' +", sex=" + sex +", lastLoginTime=" + lastLoginTime +'}';    }

定义实体类 HobbyDO.java

public class HobbyDO {private Integer id;private String hobbyName;private Integer userId;

public Integer getId() {return id;    }

public void setId(Integer id) {this.id = id;    }

public String getHobbyName() {return hobbyName;    }

public void setHobbyName(String hobbyName) {this.hobbyName = hobbyName;    }

public Integer getUserId() {return userId;    }

public void setUserId(Integer userId) {this.userId = userId;    }

@Override    public String toString() {return "HobbyDO{" +"id=" + id +", hobbyName='" + hobbyName + '\'' +", userId=" + userId +'}';    }

c.定义model类

定义类 HobbyVO.java  用来演示一对一

public class HobbyVo extends HobbyDO {private UserDO user ;

public UserDO getUser() {return user;    }

public void setUser(UserDO user) {this.user = user;    }}定义类 UserVO.java 用来演示1对多public class UserVO extends UserDO {private Listlist;

public ListgetList() {return list;    }

public void setList(Listlist) {this.list = list;    }}

d.定义mapper类文件

定义UserInfoMapper.java文件

package my.springboot.mybatis.dao;

import java.util.List;import java.util.Map;

import my.springboot.mybatis.entity.HobbyDO;import my.springboot.mybatis.entity.UserDO;import my.springboot.mybatis.model.UserVO;import org.apache.ibatis.annotations.Mapper;

@Mapperpublic interface UserInfoMapper {    UserDO get(Integer id);    List getUserVOMap(Integer id);    List getHobbyByUserId(Integer userId);}

定义HobbyMapper.java文件

package my.springboot.mybatis.dao;

import my.springboot.mybatis.entity.HobbyDO;import my.springboot.mybatis.entity.UserDO;import my.springboot.mybatis.model.HobbyVo;import org.apache.ibatis.annotations.Mapper;

import java.util.List;import java.util.Map;

@Mapperpublic interface HobbyMapper {    List getHobbyByUserId(Integer userId);    List getHobbyVOMap();}

e.定义service服务

定义IUserInfoService.java

package my.springboot.mybatis.service;

import my.springboot.mybatis.entity.UserDO;import my.springboot.mybatis.model.HobbyVo;import my.springboot.mybatis.model.UserVO;

import java.util.List;

public interface IUserInfoService {     List getUserVOMap(Integer userId);    List getHobbyMap();}


定义UserInfoService.java

package my.springboot.mybatis.service.impl;import my.springboot.mybatis.dao.HobbyMapper;import my.springboot.mybatis.dao.UserInfoMapper;import my.springboot.mybatis.entity.UserDO;import my.springboot.mybatis.model.HobbyVo;import my.springboot.mybatis.model.UserVO;import my.springboot.mybatis.service.IUserInfoService;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Service;import java.util.List;@Servicepublic class UserInfoService implements IUserInfoService {@Autowired    private UserInfoMapper mapper;@Autowired    private HobbyMapper hobbyMapper;@Override    public  List getUserVOMap(Integer id)    {return this.mapper.getUserVOMap(id);    }

@Override    public ListgetHobbyMap() {return hobbyMapper.getHobbyVOMap();    }

}


f.定义测试控制器

HomeController.java

package my.springboot.mybatis.controller;



import my.springboot.mybatis.entity.UserDO;import my.springboot.mybatis.model.HobbyVo;import my.springboot.mybatis.model.UserVO;import my.springboot.mybatis.service.IUserInfoService;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Controller;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.ResponseBody;import javax.jws.soap.SOAPBinding;import java.util.Date;import java.util.List;@Controllerpublic class HomeController {@Autowired    private IUserInfoService userInfoService;@RequestMapping("index") //注解映射请求路径    @ResponseBody //可以将java对象转为json格式的数据    public String index()    {        List vo=userInfoService.getUserVOMap(1);        List list=userInfoService.getHobbyMap();        return "Hello World !";    }}


g.定义xml文件

定义HobbyMapper.xml文件


<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE mapper PUBLIC "-////DTD Mapper 3.0//EN" "http:///dtd/mybatis-3-mapper.dtd"><mapper namespace="my.springboot.mybatis.dao.HobbyMapper"><select id="getHobbyByUserId" resultType="my.springboot.mybatis.entity.HobbyDO" parameterType="integer">       select  * from t_hobby where userId= #{id}</select><resultMap id="hobbyVOMap" type="my.springboot.mybatis.model.HobbyVo"><id property="id" column="id"/><association property="user" column="userId" javaType="my.springboot.mybatis.entity.HobbyDO"                     select="my.springboot.mybatis.dao.UserInfoMapper.get"></association></resultMap><select id="getHobbyVOMap" resultMap="hobbyVOMap" parameterType="integer">       select  * from t_hobby</select></mapper>

定义UserInfoMapper.xml
 


<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE mapper PUBLIC "-////DTD Mapper 3.0//EN" "http:///dtd/mybatis-3-mapper.dtd"><mapper namespace="my.springboot.mybatis.dao.UserInfoMapper"><select id="get" resultType="my.springboot.mybatis.entity.UserDO">   select `id`,`user_name`,`password`,`last_login_time`,`sex` from t_user where id = #{value}</select><!--跨xml文件写法 my.springboot.mybatis.dao.HobbyMapper.getHobbyByUserId-->    <resultMap id="userVOMap" type="my.springboot.mybatis.model.UserVO"><id property="id" column="id"/><collection property="list" column="id" ofType="my.springboot.mybatis.entity.HobbyDO" select="my.springboot.mybatis.dao.HobbyMapper.getHobbyByUserId"></collection></resultMap><select id="getUserVOMap" resultMap="userVOMap" parameterType="integer">       select  * from t_user</select><select id="getHobbyByUserId" resultType="my.springboot.mybatis.entity.HobbyDO" parameterType="integer">       select  * from t_hobby where userId= #{id}</select>
</mapper>




访问地址：http://localhost:8090/index
项目结构：

3、总结

resultMap用途主要有一下两点：

1、数据库字段和Java类属性映射

2、实现复杂的model类的查询

model中包含实体类使用关键字：association

<select id="getHobbyByUserId" resultType="my.springboot.mybatis.entity.HobbyDO" parameterType="integer">       select  * from t_hobby where userId= #{id}</select><resultMap id="hobbyVOMap" type="my.springboot.mybatis.model.HobbyVo"><id property="id" column="id"/><association property="user" column="userId" javaType="my.springboot.mybatis.entity.HobbyDO"                     select="my.springboot.mybatis.dao.UserInfoMapper.get"><!-- 说明：如果调用的方法不在当前xml里面，需要指明完整的mapper路径 my.springboot.mybatis.dao.UserInfoMapper.get -->           </association></resultMap><select id="getHobbyVOMap" resultMap="hobbyVOMap" parameterType="integer">       select  * from t_hobby</select>

model中包含集合使用：collection 关键代码

<resultMap id="userVOMap" type="my.springboot.mybatis.model.UserVO"><id property="id" column="id"/><collection property="list" column="id" ofType="my.springboot.mybatis.entity.HobbyDO" select="my.springboot.mybatis.dao.HobbyMapper.getHobbyByUserId"></collection></resultMap><select id="getUserVOMap" resultMap="userVOMap" parameterType="integer">   select  * from t_user</select><select id="getHobbyByUserId" resultType="my.springboot.mybatis.entity.HobbyDO" parameterType="integer">   select  * from t_hobby where userId= #{id}</select>

注意：实际的查询过程当中，并不是必须要保证数据库字段名称和实体的属性名称保持一致，如果查询语句查询字段指定别名，也是可以正常做映射的，要会灵活使用。

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