后端技術：mybatis中resultMap用法示例筆記

1、概念

resultMap屬于mybatis返回操作結果的一個標簽，可以用來映射select查詢出來結果的集合，主要作用是將實體類中的字段與數據庫表中的字段進行關聯映射。并且支持復雜的返回結果類型。

2、使用場景

2.1 屬性映射

當數據庫字段和項目中的實體屬性不一致時，可以使resultMap進行數據庫字段和實體類屬性的映射關系

比如：

     column="id" jdbcType="integer" property="id" />         column="user_name" jdbcType="VARCHAR" property="userName" />

說明：如果數據庫字段和實體類屬性一致的情況下，可以省略不寫。

2.2 實現Java復雜實體類用法

a.初始化腳本

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', '音樂', '2');INSERT INTO `t_hobby` VALUES ('1', '籃球', '1');INSERT INTO `t_hobby` VALUES ('2', '讀書', '1');

b.定義實體類

定義實體 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 +'}';    }

定義實體類 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.定義model類

定義類 HobbyVO.java? 用來演示一對一

public class HobbyVo extends HobbyDO {private UserDO user ;public UserDO getUser() {return user;    }public void setUser(UserDO user) {this.user = user;    }}定義類 UserVO.java 用來演示1對多public class UserVO extends UserDO {private Listlist;public ListgetList() {return list;    }public void setList(Listlist) {this.list = list;    }}

d.定義mapper類文件

定義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);}

定義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.定義service服務

定義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();}

定義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.定義測試控制器

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") //注解映射請求路徑    @ResponseBody //可以將java對象轉為json格式的數據    public String index()    {        List vo=userInfoService.getUserVOMap(1);        List list=userInfoService.getHobbyMap();        return "Hello World !";    }}

g.定義xml文件

定義HobbyMapper.xml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"><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>

定義UserInfoMapper.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="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文件寫法 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>

訪問地址：http://localhost:8090/index

項目結構：

3、總結

resultMap用途主要有一下兩點：

1、數據庫字段和Java類屬性映射

2、實現復雜的model類的查詢

model中包含實體類使用關鍵字：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">
<!-- 說明：如果調用的方法不在當前xml里面，需要指明完整的mapper路徑 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 關鍵代碼

<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：實際的查詢過程當中，并不是必須要保證數據庫字段名稱和實體的屬性名稱保持一致，如果查詢語句查詢字段指定別名，也是可以正常做映射的，要會靈活使用。

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