定义两个类（对应数据库内两张表） User ,Account，每个Account属于一个User
User类 及其 对应的IUserDao
package com.itheima.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 Date birthday;
private String sex;
private String address;
//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;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", username=‘" + username + ‘\‘‘ +
", birthday=" + birthday +
", sex=‘" + sex + ‘\‘‘ +
", address=‘" + address + ‘\‘‘ +
‘}‘;
}
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;
}
}
package com.itheima.dao;
import com.itheima.domain.QueryVo;
import com.itheima.domain.User;
import java.util.List;
public interface IUserDao {
/*
* 查询所有操作
* */
List<User> findAll();
/*
* 保存一条记录并返回id（直接将id赋给对应的属性）
* */
void saveUser(User user);
/*
* 更新用户
* */
void updateUser(User user);
/*
* 删除用户
* */
void deleteUser(Integer userId);
/*
* 根据Id查询User
* */
User findById(Integer userId);
/*
* 模糊查询
* */
List<User> findByName(String username);
/*
* 查询User总数
* */
int findTotal();
/*
* 根据queryVo查询中的条件查询用户
* */
List<User> findByVo(QueryVo vo);
/*
* 根据传入参数条件查询
* @param user 查询的条件：有可能有用户名，有可能有性别，也有可能有地址，可能啥都没有
* */
List<User> findUserByCondition(User user);
/*
* 根据queryVo中提供的id集合查询用户信息
* */
List<User> findUserInIds(QueryVo vo);
}
Account类 及其对应的 IAccountDao
package com.itheima.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像引用
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 +
‘}‘;
}
}
package com.itheima.dao;
import com.itheima.domain.Account;
import com.itheima.domain.AccountUser;
import java.util.List;
public interface IAccountDao {
/*
* 查询所有Account
* */
List<Account> findAll();
/*
* 查询所有账户，并且带有用户名和地址
* */
List<AccountUser> findAllAccountUser();
}
一对一(多对一)的关系查询：查询Account时也要查询出所属User的信息
显然每个Account对应了一个User
//从表实体应该包含一个主表实体的对像引用
private User user;
下面是IAccountDao.xml 对于 findAll方法的配置
<?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.itheima.dao.IAccountDao">
<!--定义封装account和user的resultMap-->
<resultMap id="accountUserMap" type="com.itheima.domain.Account">
<id property="id" column="aid"></id>
<result property="uid" column="uid"></result>
<result property="money" column="money"></result>
<!--一对一关系映射，配置封装user的内容，column：外键，javaType:联系对象的全限定类名-->
<association property="user" column="uid" javaType="com.itheima.domain.User">
<id property="id" column="id"></id>
<result column="username" property="username"></result>
<result column="address" property="address"></result>
<result column="sex" property="sex"></result>
<result column="birthday" property="birthday"></result>
</association>
</resultMap>
<!--查询所有Account并获得对应User信息(多对一标准写法)-->
<select id="findAll" resultMap="accountUserMap">
select u.*, a.id as aid, a.uid, a.money
from account as a, user as u
where u.id = a.uid
</select>
<!--查询所有Account，同时包含用户名和地址信息-->
<select id="findAllAccountUser" resultType="com.itheima.domain.AccountUser">
select a.*,u.username,u.address from account as a, user as u
where a.uid = u.id;
</select>
</mapper>
测试代码
/*
* 查询所有Account并获得对应User信息(多对一标准写法)
* */
@Test
public void testFindAll(){
List<Account> accounts = accountDao.findAll();
for(Account account:accounts)
System.out.println(account+account.getUser().toString());
}
一对多的关系查询：查询User时查询所有和其相关的Account集合
类似Account类内声明一个User的引用，User内也声明了一个Account类的集合
//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;
IUserDao.xml 关于 findAll方法的配置
<resultMap id="userAccountMap" type="com.itheima.domain.User">
<id property="id" column="id"></id>
<result property="username" column="username"></result>
<result property="address" column="address"></result>
<result property="sex" column="sex"></result>
<result property="birthday" column="birthday"></result>
<!--配置user对象中accounts集合的映射,ofTpe:集合中元素的全限定类名-->
<collection property="accounts" ofType="com.itheima.domain.Account">
<id property="id" column="aid"></id>
<result property="uid" column="uid"></result>
<result property="money" column="money"></result>
</collection>
</resultMap>
<!--配置查询所有-->
<select id="findAll" resultMap="userAccountMap">
select * from user as u left outer join account as a
on u.id = a.uid
</select>
测试方法
@Test
public void testFindAll()throws Exception{
//5.使用代理对象执行方法
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());
}
}
原文地址：https://www.cnblogs.com/zsben991126/p/12588800.html
时间： 2024-10-21 14:49:29