小程序三方平台开发: 解析小程序开发的未来趋势和机遇
588
2023-03-21
Mybatis一对一延迟加载实现过程解析
需求:用户和账户一对一关系,查询账户时实现用户的延迟加载
思路:根据id查询,需要延迟加载的一方
1、用户实体类
package com.yl.bean;
import java.io.Serializable;
import java.sql.Date;
import java.util.List;
/**
* 用户实体类
*/
public class User implements Serializable {
private Integer id;//id
private String username;//用户名
private Date birthday;//生日
private String sex;//性别
private String address;//地址
private Account account;//用户所拥有的账户
public User() {
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id =http:// http://id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public Date getBirthday() {
return birPThhnQoFOthday;
}
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;
}
public Account getAccount() {
return account;
}
public void setAccount(Account account) {
this.account = account;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", username='" + username + '\'' +
", birthday=" + birthday +
", sex='" + sex + '\'' +
", address='" + address + '\'' +
'}';
}
}
2、账户实体类
package com.yl.bean;
import java.io.Serializable;
/**
* 账户实体类
*/
public class Account implements Serializable {
private Integer id;//账户id
private Integer uid;//用户id
private Double money;//余额
private User user;//账户所属用户
public Account() {
}
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 +
'}';
}
}
3、用户持久层接口
package com.yl.dao;
import com.yl.bean.User;
import java.util.List;
/**
* 用户持久层接口
*/
public interface IUserDao {
/**
* 查询所有用户
*/
List
/**
* 根据id查询用户
*/
User queryById(int id);
}
4、账户持久层接口
package com.yl.dao;
import com.yl.bean.Account;
import com.yl.bean.User;
import java.util.List;
/**
* 账户持久层接口
*/
public interface IAccountDao {
/**
* 查询所有账户
*/
List
}
5、全局配置文件
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
6、用户映射配置文件
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
SELECT * FROM USER u LEFT OUTER JOIN account a ON u.`id`=a.`UID`
select * from user where id=#{id}
7、账户映射配置文件
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
SELECT * FROM account
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