概述
最近在整理笔记，就把mybaits 中一对多，以及多对一查询详细的捋一遍。
- 首先 准备sql 数据 user(用户表) account(账户表) 一个用户可以有多个账户，一个账户只属于一个用户；
- 建立maven 工程 导入相关依赖 ，mybatis,mysql,junit,log4j；
- 建立实体类User和Account；
- 编写Dao,以及映射文件和主配置文件，下面上代码
- 编写测试类
项目的结构为：
1）sql数据-----
/*
SQLyog Ultimate v12.09 (64 bit)
MySQL - 5.5.40 : Database - mybatis
*********************************************************************
*/
/*!40101 SET NAMES utf8 */;
/*!40101 SET SQL_MODE=''*/;
/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;
CREATE DATABASE /*!32312 IF NOT EXISTS*/`mybatis` /*!40100 DEFAULT CHARACTER SET utf8 */;
USE `mybatis`;
/*Table structure for table `account` */
DROP TABLE IF EXISTS `account`;
CREATE TABLE `account` (
`ID` int(11) NOT NULL COMMENT '编号',
`UID` int(11) DEFAULT NULL COMMENT '用户编号',
`MONEY` double DEFAULT NULL COMMENT '金额',
PRIMARY KEY (`ID`),
KEY `FK_Reference_8` (`UID`),
CONSTRAINT `FK_Reference_8` FOREIGN KEY (`UID`) REFERENCES `user` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
/*Data for the table `account` */
insert into `account`(`ID`,`UID`,`MONEY`) values (1,41,1000),(2,41,1000),(3,48,2000);
/*Table structure for table `user` */
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`username` varchar(32) NOT NULL COMMENT '用户名称',
`birthday` datetime DEFAULT NULL COMMENT '生日',
`sex` char(1) DEFAULT NULL COMMENT '性别',
`address` varchar(256) DEFAULT NULL COMMENT '地址',
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=55 DEFAULT CHARSET=utf8;
/*Data for the table `user` */
insert into `user`(`id`,`username`,`birthday`,`sex`,`address`) values (41,'11111','2018-02-27 17:47:08','男','北京'),(42,'小二王','2018-03-02 15:09:37','女','北京金燕龙'),(43,'小二王','2018-03-04 11:34:34','男','北京金燕龙'),(45,'传智播客','2018-03-04 12:04:06','男','北京金燕龙'),(48,'小马宝莉','2018-03-08 11:44:00','女','北京修正'),(54,'黄顺','2019-04-29 09:41:15','男','安徽');
/*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
/*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
/*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;
/*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;
2）建立maven 工程导入相应依赖
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>cn.hs</groupId>
<artifactId>mybatis_one_t_omore</artifactId>
<version>1.0-SNAPSHOT</version>
<dependencies>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.4.5</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.32</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
</dependencies>
</project>3）创建实体类
user:
package domain;
import java.util.Date;
import java.util.List;
/**
* @Author: huangshun
* @Date: 2019/4/30 10:28
* @Version 1.0
*/
public class User {
private Integer id;
private String username;
private Date birthday;
private String sex;
private String address;
private List<Account> accounts;// 一对多 一个用户包含多个账户
@Override
public String toString() {
return "User{" +
"id=" + id +
", username='" + username + ''' +
", birthday=" + birthday +
", sex='" + sex + ''' +
", address='" + address + ''' +
", accounts=" + accounts +
'}';
}
public List<Account> getAccounts() {
return accounts;
}
public void setAccounts(List<Account> accounts) {
this.accounts = accounts;
}
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 Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
}
--------------------------------------------------------------------------------------
Account:
package domain;
/**
* @Author: huangshun
* @Date: 2019/4/30 10:39
* @Version 1.0
*/
public class Account {
/**
* 账户的实体类 一个用户对应 多个账户
*/
private Integer id;
private Integer uid;
private double money;
private User user;
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
@Override
public String toString() {
return "Account{" +
"id=" + id +
", uid=" + uid +
", money=" + money +
", user=" + user +
'}';
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public Integer getUid() {
return uid;
}
public void setUid(Integer uid) {
this.uid = uid;
}
public double getMoney() {
return money;
}
public void setMoney(double money) {
this.money = money;
}
}
4)编写dao
UserDao:
-----------------------------------------------------------------------------------------
package dao;
import domain.User;
import java.util.List;
/**
* @Author: huangshun
* @Date: 2019/4/30 10:31
* @Version 1.0
*/
public interface UserDao {
/**
* 查询所有用户信息 包含用户的账户--
* @return
*/
List<User> findAll();
}
-----------------------------------------------------------------------------------------
AccountDao:
package dao;
import domain.Account;
import java.util.List;
/**操作账户的Dao
* @Author: huangshun
* @Date: 2019/4/30 10:42
* @Version 1.0
*/
public interface AccountDao {
/**
* 查询所有账户的信息 包括账户所属于的用户 一对一的查询
* @return
*/
List<Account> findAllAccount();
}
编写配置文件
这里较为重要：
UserDaoMapping.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="dao.UserDao">
<resultMap id="userMap" type="domain.User">
<id property="id" column="id"></id>
<result property="username" column="username"></result>
<result property="sex" column="sex"></result>
<result property="address" column="address"></result>
<result property="birthday" column="birthday"></result>
<!--配置账户数据的集合 -->
<collection property="accounts" ofType="domain.Account">
<!--
注意：
这里colum="aid"为什么要这么写 因为上面user那边已经定义了一个id
若这里再定义为id 就会把user的id 封装到account的id里，
所以这里定义的为aid 同时sql语句里也要 a.id as aid
理论上没变 属性对应 数据库字段名 只是现在字段是aid了
-->
<id property="id" column="aid"></id>
<result property="uid" column="uid"></result>
<result property="money" column="money"></result>
</collection>
</resultMap>
<select id="findAll" resultMap="userMap">
select u.*,a.id as aid,a.money from user u left join account a on u.id=a.uid;
</select>
</mapper>
--------------------------------------------------------------------------------------
AccountDaoMapping.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="dao.AccountDao">
<resultMap id="accountMap" type="domain.Account">
<id property="id" column="id"></id>
<result property="uid" column="uid"/>
<result property="money" column="money"/>
<!-- 它是用于指定从表方的引用实体属性的
property: 对应account实体类的user 属性
javaType：指的是类型
-->
<association property="user" javaType="domain.User">
<!--注意：
这里colum="uid"为什么要这么写 因为上面账户那边已经定义了一个id
若这里再定义为id 就会把账户的id 封装到user的id里，
所以这里定义的为uid 同时sql语句里也要 u.id as uid
理论上没变 属性对应 数据库字段名 只是现在字段是uid了
-->
<id property="id" column="uid"></id>
<result property="username" column="username"></result>
<result property="birthday" column="birthday"></result>
<result property="sex" column="sex"></result>
<result property="address" column="address"></result>
</association>
</resultMap>
<!--查询所有账户信息 同时包括账户所属的联系人信息 -->
<!--一对一 一个账户对应一个用户 -->
<select id="findAllAccount" resultMap="accountMap">
SELECT a.*,u.id as uid,u.username,u.address FROM account AS a,USER AS u WHERE a.uid=u.id;
<!--select u.*,a.id as aid,a.uid,a.money from account a,user u where a.uid =u.id;-->
</select>
</mapper>
--------------------------------------------------------------------------------------
SqlMapConfig.xml
---------------------------------------------------------------------------------------
<?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">
<!-- mybatis的主配置文件 -->
<configuration>
<!-- 配置环境 -->
<environments default="mysql">
<!-- 配置mysql的环境-->
<environment id="mysql">
<!-- 配置事务的类型-->
<transactionManager type="JDBC"></transactionManager>
<!-- 配置数据源（连接池） -->
<dataSource type="POOLED">
<!-- 配置连接数据库的4个基本信息 -->
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mybatis"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
<!-- 指定映射配置文件的位置，映射配置文件指的是每个dao独立的配置文件 -->
<mappers>
<mapper resource="UserDaoMapping.xml"/>
<mapper resource="AccountDaoMapping.xml"></mapper>
</mappers>
</configuration>
5）编写测试类
TestUser:
-----------------------------------------------------------------------------------------import dao.UserDao;
import domain.User;
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 org.junit.After;
import org.junit.Before;
import org.junit.Test;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
/**
* @Author: huangshun
* @Date: 2019/4/30 10:34
* @Version 1.0
*/
public class TestUser {
InputStream in;
SqlSession sqlSession;
SqlSessionFactory factory;
UserDao dao;
@Before
public void testBefore() throws IOException {
in= Resources.getResourceAsStream("SqlMapConfig.xml");
factory =new SqlSessionFactoryBuilder().build(in);
sqlSession = factory.openSession();
dao = sqlSession.getMapper(UserDao.class);
}
@After
public void testAfter() throws IOException {
sqlSession.close();
in.close();
}
/**
* 测试查询所有用户信息 一对多 一个用户可以包含多个账户
*/
@Test
public void testFindAll(){
List<User> users = dao.findAll();
for (User user : users) {
System.out.println(user);
/*输出结果
User{id=41, username='11111', birthday=Tue Feb 27 17:47:08 CST 2018, sex='男', address='北京', accounts=[Account{id=1, uid=null, money=1000.0, user=null}, Account{id=2, uid=null, money=1000.0, user=null}]}
User{id=42, username='小二王', birthday=Fri Mar 02 15:09:37 CST 2018, sex='女', address='北京金燕龙', accounts=[]}
User{id=43, username='小二王', birthday=Sun Mar 04 11:34:34 CST 2018, sex='男', address='北京金燕龙', accounts=[]}
User{id=45, username='客', birthday=Sun Mar 04 12:04:06 CST 2018, sex='男', address='北京金燕龙', accounts=[]}
User{id=48, username='小马宝莉', birthday=Thu Mar 08 11:44:00 CST 2018, sex='女', address='北京修正', accounts=[Account{id=3, uid=null, money=2000.0, user=null}]}
User{id=54, username='黄顺', birthday=Mon Apr 29 09:41:15 CST 2019, sex='男', address='安徽', accounts=[]}
*
*
*
*
* */
}
}
}
-----------------------------------------------------------------------------------------TestAccount:
import dao.AccountDao;
import dao.UserDao;
import domain.Account;
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 org.junit.After;
import org.junit.Before;
import org.junit.Test;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
/**
* @Author: huangshun
* @Date: 2019/4/30 11:06
* @Version 1.0
*/
public class TestAccount {
InputStream in;
SqlSession sqlSession;
SqlSessionFactory factory;
AccountDao dao;
@Before
public void testBefore() throws IOException {
in= Resources.getResourceAsStream("SqlMapConfig.xml");
factory =new SqlSessionFactoryBuilder().build(in);
sqlSession = factory.openSession();
dao = sqlSession.getMapper(AccountDao.class);
}
@After
public void testAfter() throws IOException {
sqlSession.close();
in.close();
}
/**
* 查询所有账户的信息，同时包含用户信息 多对一（一对一）
*/
@Test
public void testfindAllAccount(){
List<Account> accounts = dao.findAllAccount();
for (Account account : accounts) {
System.out.println(account);
/*测试结果：
Account{id=1, uid=41, money=1000.0, user=User{id=41, username='11111', birthday=null, sex='null', address='北京', accounts=null}}
Account{id=2, uid=41, money=1000.0, user=User{id=41, username='11111', birthday=null, sex='null', address='北京', accounts=null}}
Account{id=3, uid=48, money=2000.0, user=User{id=48, username='小马宝莉', birthday=null, sex='null', address='北京修正', accounts=null}}
*
* */
}
}
}
至此，本案例结束
最后
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