Mybatis 系列7-多表操作
简单说明
一对一：人和身份证，一个人只能有一个身份证，一个身份证也只能被一个人拥有。
多对多：老师和学生，一个学生可以有多个老师，一个老师可以有多个学生。
多对一：用户和订单是一对多，一个用户可以下多个订单
订单和用户是多对一，多个订单可以属于同一个用户。
创建两个表：User和Account
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=49 DEFAULT CHARSET=utf8;
/*Data for the table `user` */
insert into `user`(`id`,`username`,`birthday`,`sex`,`address`) values (41,'老王','2018-02-27 17:47:08','男','山东'),(42,'小二王','2018-03-02 15:09:37','女','上海'),(43,'小二王','2018-03-04 11:34:34','女','南京'),(45,'张三','2018-03-04 12:04:06','男','南京'),(46,'老王','2018-03-07 17:37:26','男','北京'),(48,'小宝','2018-03-08 11:44:00','女','上海');
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 (1,46,1000),(2,45,1000),(3,46,2000);
一对一
在实体操作，虽然不建议这么操作，扩展的AccountUser类：
package com.mantishell.domain;
public class AccountUser extends User {
private String username;
private String address;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
@Override
public String toString() {
return super.toString()+" AccountUser{" +
"username='" + username + '\'' +
", address='" + address + '\'' +
'}';
}
}
Account实体类
package com.mantishell.domain;
import java.io.Serializable;
public class Account implements Serializable {
private Integer id;
private Integer uid;
private Double money;
//从表实体应该包含一个主表实体的对象引用
private User user;
public User getUser() {
return user;
}
public void setUser(User user) {
this.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;
}
@Override
public String toString() {
return "Account{" +
"id=" + id +
", uid=" + uid +
", money=" + money +
'}';
}
}
IAccountDao:
package com.mantishell.dao;
import com.mantishell.domain.Account;
import com.mantishell.domain.AccountUser;
import java.util.List;
public interface IAccountDao {
/**
* 查询所有账户，同时还要获取到当前账户的所属用户信息
* @return
*/
List<Account> findAll();
/**
* 查询所有账户，并且带有用户名称和地址信息
* @return
*/
List<AccountUser> findAllAccount();
}
Account的配置文件
<?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="com.mantishell.dao.IAccountDao">
<!-- 配置 实体类的属性名和数据库中字段名的对应关系-->
<resultMap id="accountUserMap" type="account">
<!--主键字段的对应-->
<id property="id" column="aid"/>
<!--非主键字段的对应-->
<result property="uid" column="uid"/>
<result property="money" column="money"/>
<!-- 一对一的关系映射：配置封装user的内容-->
<association property="user" column="uid" javaType="user">
<id property="id" column="id"/>
<result property="username" column="username"/>
<result property="address" column="address"/>
<result property="sex" column="sex"/>
<result property="birthday" column="birthday"/>
</association>
</resultMap>
<!-- 查询所有，需要将两张表结合起来 -->
<select id="findAll" resultMap="accountUserMap">
select u.*,a.id as aid,a.uid,a.money from account a , user u where u.id = a.uid;
</select>
<!--查询所有账户同时包含用户名和地址信息-->
<select id="findAllAccount" resultType="accountuser">
select a.*,u.username,u.address from account a , user u where u.id = a.uid;
</select>
</mapper>
测试：
@Test
public void testFindAll(){
List<Account> accounts = accountDao.findAll();
for(Account account : accounts){
System.out.println("--------每个account的信息------------");
System.out.println(account);
System.out.println(account.getUser());
}
}
一对多
User实体类：
package com.mantishell.domain;
import java.io.Serializable;
import java.util.Date;
import java.util.List;
public class User implements Serializable {
private Integer id;
private String username;
private String address;
private String sex;
private Date birthday;
//一对多关系映射：主表实体应该包含从表实体的集合引用
private List<Account> 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 String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", username='" + username + '\'' +
", address='" + address + '\'' +
", sex='" + sex + '\'' +
", birthday=" + birthday +
'}';
}
}
持久层接口
IUserDao：
package com.mantishell.dao;
import com.mantishell.domain.User;
import java.util.List;
public interface IUserDao {
/**
* 查询所有用户，同时获取到用户下所有账户的信息
* @return
*/
List<User> findAll();
User findById(Integer userId);
}
User的配置文件
<?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">
<!--namespace：dao的全限定类名-->
<mapper namespace="com.mantishell.dao.IUserDao">
<!-- 配置 实体类的属性名和数据库中字段名的对应关系-->
<resultMap id="userAccountMap" type="user">
<!--主键字段的对应-->
<id property="id" column="id"></id>
<!--非主键字段的对应-->
<result property="username" column="username" />
<result property="address" column="address"/>
<result property="sex" column="sex"/>
<result property="birthday" column="birthday"/>
<!-- collection 是用于建立一对多集合属性的对应关系
javaType 用于指定字段属性，比如java.util.List
ofType 用于指定集合元素的数据类型，即这个List存放的javaBean的类型 -->
<collection property="accounts" ofType="account">
<!--主键字段的对应-->
<id property="id" column="aid"/>
<!--非主键字段的对应-->
<result property="uid" column="uid"/>
<result property="money" column="money"/>
</collection>
</resultMap>
<!-- 查询所有 -->
<select id="findAll" resultMap="userAccountMap">
select * from user u left outer join account a on u.id = a.uid
</select>
<!-- 根据id查询用户 -->
<select id="findById" parameterType="INT" resultType="user">
select * from user where id = #{uid}
</select>
</mapper>
测试：
@Test
public void testFindAll(){
List<User> users = userDao.findAll();
for(User user : users){
System.out.println("-----每个用户的信息------");
System.out.println(user);
System.out.println(user.getAccounts());
}
}
