【MyBatis】MyBatis 多表操作
2024-09-27 10:09:15
MyBatis 多表操作
一对一查询
需求:查询所有账户信息,关联查询下单用户信息。
注意:因为一个账户信息只能供某个用户使用,所以从查询账户信息出发关联查询用户信息为一对一查询。如果从用户信息出发关联查询用户下的账户信息则为一对多查询,因为一个用户可以有多个账户。
可以使用 resultMap,定义专门的 resultMap 用于映射一对一查询结果。
定义账户信息的数据表
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; insert into `account`(`ID`,`UID`,`MONEY`) values (1,41,1000),(2,45,1000),(3,41,2000);
定义账户信息的实体类
package cn.parzulpan.domain; import java.io.Serializable; /**
* @Author : parzulpan
* @Time : 2020-12
* @Desc :
*/ public class Account implements Serializable {
private Integer id;
private Integer uid;
private Double money;
private 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;
} 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 +
'}';
}
}
编写 SQL
select u.*, a.id as aid, a.uid, a.money
from account a, user u
where a.uid = u.id;
定义账户的持久层 DAO 接口
package cn.parzulpan.dao; import cn.parzulpan.domain.Account; import java.util.List; /**
* @Author : parzulpan
* @Time : 2020-12
* @Desc :
*/ public interface AccountDAO { /**
* 查询所有账户,同时获取账户的所属用户名称以及它的地址信息
* @return
*/
List<Account> findAll();
}
配置 AccountDAO.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="cn.parzulpan.dao.AccountDAO"> <!-- 建立对应关系 -->
<resultMap id="accountMap" type="account">
<id column="aid" property="id"/>
<result column="uid" property="uid"/>
<result column="money" property="money"/> <!-- 用于指定从数据表方的引用实体属性 -->
<association property="user" javaType="user">
<id column="id" property="id"/>
<result column="username" property="username"/>
<result column="sex" property="sex"/>
<result column="birthday" property="birthday"/>
<result column="address" property="address"/>
</association>
</resultMap> <select id="findAll" resultMap="accountMap">
select u.*, a.id as aid, a.uid, a.money
from account a, user u
where a.uid = u.id;
</select>
</mapper>
测试
package cn.parzulpan.test; import cn.parzulpan.dao.AccountDAO;
import cn.parzulpan.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 : parzulpan
* @Time : 2020-12
* @Desc : 多表查询
*/ public class MyBatisQueryTest {
private InputStream is;
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
private SqlSessionFactory factory;
private SqlSession session;
private AccountDAO accountDAO; @Before
public void init() throws IOException {
is = Resources.getResourceAsStream("SqlMapConfig.xml");
factory = builder.build(is);
session = factory.openSession();
accountDAO = session.getMapper(AccountDAO.class);
} @After
public void destroy() throws IOException {
session.commit(); // 事务提交
session.close();
is.close();
} @Test
public void findAllTest() {
List<Account> accounts = accountDAO.findAll();
for (Account account : accounts) {
System.out.println(account);
System.out.println(account.getUser());
}
}
}
一对多查询
需求:查询所有用户信息及用户关联的账户信息。
分析:用户信息和他的账户信息为一对多关系,并且查询过程中如果用户没有账户信息,此时也要将用户信息查询出来,所以左外连接查询比较合适。
编写 SQL
select u.*, a.id as id, a.uid, a.money
from user u left join account a on u.id = a. uid;
User 类加入
List<Account>
用户持久层 DAO 接口中加入查询方法
/**
* 查询所有用户,同时获取出每个用户下的所有账户信息
* @return
*/
List<User> findAllAndAccount();
配置 UserDAO.xml 文件
<resultMap id="userMap" type="user">
<id column="id" property="id"/>
<result column="username" property="username"/>
<result column="address" property="address"/>
<result column="sex" property="sex"/>
<result column="birthday" property="birthday"/> <!-- collection 是用于建立一对多中集合属性的对应关系 ofType 用于指定集合元素的数据类型 -->
<collection property="accounts" ofType="account">
<id column="aid" property="id"/>
<result column="uid" property="uid"/>
<result column="money" property="money"/>
</collection>
</resultMap> <select id="findAllAndAccount" resultMap="userMap">
select u.*, a.id as aid, a.uid, a.money
from user u left join account a on u.id = a. uid;
</select>
测试
@Test
public void findAllAndAccountTest() {
List<User> users = userDAO.findAllAndAccount();
for (User user : users) {
System.out.println();
System.out.println("----- " + user.getUsername() + " -----");
System.out.println(user);
System.out.println(user.getAccounts());
}
}
多对多查询
需求:实现查询所有对象并且加载它所分配的用户信息。
注意:查询角色我们需要用到Role表,但角色分配的用户的信息我们并不能直接找到用户信息,而是要通过中间表(USER_ROLE 表)才能关联到用户信息。
定义相关的数据表
# ----- DROP TABLE IF EXISTS `role`; CREATE TABLE `role` (
`ID` int(11) NOT NULL COMMENT '编号',
`ROLE_NAME` varchar(30) default NULL COMMENT '角色名称',
`ROLE_DESC` varchar(60) default NULL COMMENT '角色描述',
PRIMARY KEY (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8; insert into `role`(`ID`,`ROLE_NAME`,`ROLE_DESC`) values (1,'院长','管理整个学院'),(2,'总裁','管理整个公司'),(3,'校长','管理整个学校'); # ----- DROP TABLE IF EXISTS `user_role`; CREATE TABLE `user_role` (
`UID` int(11) NOT NULL COMMENT '用户编号',
`RID` int(11) NOT NULL COMMENT '角色编号',
PRIMARY KEY (`UID`,`RID`),
KEY `FK_Reference_10` (`RID`),
CONSTRAINT `FK_Reference_10` FOREIGN KEY (`RID`) REFERENCES `role` (`ID`),
CONSTRAINT `FK_Reference_9` FOREIGN KEY (`UID`) REFERENCES `user` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8; insert into `user_role`(`UID`,`RID`) values (41,1),(45,1),(41,2);
定义角色信息的实体类
package cn.parzulpan.domain; import java.io.Serializable;
import java.util.List; /**
* @Author : parzulpan
* @Time : 2020-12
* @Desc : 角色实体类
*/ public class Role implements Serializable {
private Integer roleId;
private String roleName;
private String roleDesc; private List<User> users; //多对多的关系映射:一个角色可以赋予多个用户 public Integer getRoleId() {
return roleId;
} public void setRoleId(Integer roleId) {
this.roleId = roleId;
} public String getRoleName() {
return roleName;
} public void setRoleName(String roleName) {
this.roleName = roleName;
} public String getRoleDesc() {
return roleDesc;
} public void setRoleDesc(String roleDesc) {
this.roleDesc = roleDesc;
} public List<User> getUsers() {
return users;
} public void setUsers(List<User> users) {
this.users = users;
} @Override
public String toString() {
return "Role{" +
"roleId=" + roleId +
", roleName='" + roleName + '\'' +
", roleDesc='" + roleDesc + '\'' +
", users=" + users +
'}';
}
}
编写 RoleDAO 持久层接口
package cn.parzulpan.dao; import cn.parzulpan.domain.Role; import java.util.List; /**
* @Author : parzulpan
* @Time : 2020-12
* @Desc :
*/ public interface RoleDAO { /**
* 查询所有角色
* @return
*/
List<Role> findAll();
}编写映射文件
<?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="cn.parzulpan.dao.RoleDAO"> <!-- 建立对应关系 -->
<resultMap id="roleMap" type="role">
<id property="roleId" column="rid"/>
<result property="roleName" column="role_name"/>
<result property="roleDesc" column="role_desc"/>
<collection property="users" ofType="user">
<id column="id" property="id"/>
<result column="username" property="username"/>
<result column="address" property="address"/>
<result column="sex" property="sex"/>
<result column="birthday" property="birthday"/>
</collection>
</resultMap> <select id="findAll" resultMap="roleMap">
select r.id as rid, r.role_name, r.role_desc, u.*
from role r left outer join user_role ur on r.id = ur.rid left outer join user u on u.id = ur.uid
</select>
</mapper>
测试
package cn.parzulpan.test; import cn.parzulpan.dao.AccountDAO;
import cn.parzulpan.dao.RoleDAO;
import cn.parzulpan.domain.Account;
import cn.parzulpan.domain.Role;
import cn.parzulpan.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 : parzulpan
* @Time : 2020-12
* @Desc : 多表查询
*/ public class MyBatisManyQueryTest {
private InputStream is;
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
private SqlSessionFactory factory;
private SqlSession session;
private RoleDAO roleDAO; @Before
public void init() throws IOException {
is = Resources.getResourceAsStream("SqlMapConfig.xml");
factory = builder.build(is);
session = factory.openSession();
roleDAO = session.getMapper(RoleDAO.class);
} @After
public void destroy() throws IOException {
session.commit(); // 事务提交
session.close();
is.close();
} @Test
public void findAllTest() {
List<Role> roles = roleDAO.findAll();
for (Role role : roles) {
System.out.println();
System.out.println("----- " + " -----");
System.out.println(role);
if (role != null) {
System.out.println(role.getUsers());
}
}
}
}
练习和总结
最新文章
- 去除html的&;nbsp;标签
- maven配置发布仓库
- ITOO 第一个任务,新建界面
- 无法识别的属性“targetFramework”的解决方法
- Linux时间子系统之六:高精度定时器(HRTIMER)的原理和实现
- java基础-003
- WinSock异步IO模型之Select
- mongodb3 权限认证问题总结
- Pi
- 最受欢迎的iOS第三方SDK
- zabbix web监控模板
- 读《Linux内核设计与实现》我想到了这些书
- 编译部署 Mysql 5.7
- LeetCode第十题-正则表达式匹配
- 重温IO
- 疑难杂症:Java中Scanner连续获取int和String型发生错误.
- Your ApplicationContext is unlikely to start due to a @ComponentScan of the default
- C#的发展历程 -- 系列介绍
- DDD简明入门之道 - 开篇
- 003 关于shell基础,大数据的前期准备
热门文章
- Panda Global获悉,美国承诺4年内明确区块链数字资产监管方式!
- 【题解】The Great Divide [Uva10256]
- 题解-洛谷P5410 【模板】扩展 KMP(Z 函数)
- Angular:自定义属性指令
- 前置机器学习(四):一文掌握Pandas用法
- window+nginx+php
- 学好Spark/Kafka必须要掌握的Scala技术点(一)变量、表达式、循环、Option、方法和函数,数组、映射、元组、集合
- 总结 Visual Studio 2019 发布以来 XAML 工具的改进
- NFS文件共享服务器搭建
- SpringCloud 源码系列(4)—— 负载均衡 Ribbon