前言
这次大创有个需求，在数据库建表时发现，user表与project表的关系表 user_project的主键为复合主键：
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create table user_project( user_id int(20), project_id int(20), timestamp varchar (50), donate_money double(10,2), primary key (user_id,project_id)); |
在网上看了几篇博客，以及在spring boot干货群咨询（感谢夜升额耐心解答）过后总算是做出来了。这里做个总结，方便日后查阅。
正文
这里采用@idclass注解的方式来实现复合主键；
思路
- 编写一个复合主键类userprojectmultikeysclass;
- 通过@idclass注释在实体中标注复合主键;
- 可以通过entitymanager获取数据，或者是直接在repository 里写方法；
实现
复合主键类
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package com.hzy.model;import java.io.serializable;/** * created by huangzhenyang on 2017/9/7. * userproject的复合主键类 * * @param userid * @param projectid * @param timestamp * 由这三个共同组成复合主键 */public class userprojectmultikeysclass implements serializable { private integer userid; private integer projectid; private string timestamp; //constructor public userprojectmultikeysclass() { } public userprojectmultikeysclass(integer userid, integer projectid, string timestamp) { this.userid = userid; this.projectid = projectid; this.timestamp = timestamp; } //setter and getter public integer getuserid() { return userid; } public void setuserid(integer userid) { this.userid = userid; } public integer getprojectid() { return projectid; } public void setprojectid(integer projectid) { this.projectid = projectid; } public string gettimestamp() { return timestamp; } public void settimestamp(string timestamp) { this.timestamp = timestamp; } // ***重写hashcode与equals方法*** 划重点！ @override public int hashcode() { final int prime = 31; int result = 1; result = prime * result + ((userid == null) ? 0 : userid.hashcode()); result = prime * result + ((projectid == null) ? 0 : projectid.hashcode()); result = prime * result + ((timestamp == null) ? 0 : timestamp.hashcode()); return result; } @override public boolean equals(object obj){ if(this == obj){ return true; } if(obj == null){ return false; } if(getclass() != obj.getclass()){ return false; } final userprojectmultikeysclass other = (userprojectmultikeysclass)obj; if(userid == null){ if(other.userid != null){ return false; } }else if(!userid.equals(other.userid)){ return false; } if(projectid == null){ if(other.projectid != null){ return false; } }else if(!projectid.equals(other.projectid)){ return false; } if(timestamp == null){ if(other.timestamp != null){ return false; } }else if(!timestamp.equals(other.timestamp)){ return false; } return true; }} |
注意：
复合主键类必须满足：
1. 实现serializable接口;
2. 有默认的public无参数的构造方法;
3. 重写equals和hashcode方法。equals方法用于判断两个对象是否相同，entitymanger通过find方法来查找entity时，是根据equals的返回值来判断的。hashcode方法返回当前对象的哈希码;
实体类
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package com.hzy.model;import javax.persistence.entity;import javax.persistence.id;import javax.persistence.idclass;import javax.persistence.table;import java.io.serializable;/** * created by huangzhenyang on 2017/9/7. * */@entity@table(name = "user_project")@idclass(userprojectmultikeysclass.class)public class userproject implements serializable { private double donatemoney; private integer userid; private integer projectid; private string timestamp; @id public integer getuserid(){ return this.userid; } @id public integer getprojectid(){ return this.projectid; } @id public string gettimestamp(){ return this.timestamp; } //getter and setter public double getdonatemoney() { return donatemoney; } public void setdonatemoney(double donatemoney) { this.donatemoney = donatemoney; } public void setuserid(integer userid) { this.userid = userid; } public void setprojectid(integer projectid) { this.projectid = projectid; } public void settimestamp(string timestamp) { this.timestamp = timestamp; } @override public string tostring() { return "userproject{" + "donatemoney=" + donatemoney + ", userid=" + userid + ", projectid=" + projectid + ", timestamp='" + timestamp + '\'' + '}'; }} |
注意：
1. @idclass标注用于标注实体所使用主键规则的类；
2. 在实体中同时标注主键的属性，比如这段代码中的userid,projectid以及timestamp ；
获取数据
方法一： 通过entitymanager获取，比如方法testuserprojectrepository()
方法二：通过repository获取；这里记得在extends jparepository<userproject,userprojectmultikeysclass>时把id的主键类指定为复合主键类userprojectmultikeysclass
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public interface userprojectrepository extends jparepository<userproject,userprojectmultikeysclass>{ // 根据用户id,找出用户参与的所有userproject // test pass list<userproject> findbyuserid(integer userid); // 根据项目id,找出参与项目的所有userproject // test pass list<userproject> findbyprojectid(integer projectid); // 根据用户id和项目id 找出所有的userproject // test pass list<userproject> findbyuseridandprojectid(integer userid,integer projectid);} |
单元测试的代码
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package com.hzy;import com.hzy.model.userproject;import com.hzy.model.userprojectmultikeysclass;import com.hzy.repository.userprojectrepository;import com.hzy.service.userprojectservice;import com.hzy.service.userservice;import org.junit.test;import org.junit.runner.runwith;import org.springframework.beans.factory.annotation.autowired;import org.springframework.boot.test.context.springboottest;import org.springframework.test.context.junit4.springrunner;import javax.persistence.entitymanager;import javax.persistence.persistencecontext;import javax.transaction.transactional;import java.util.list;/** * created by huangzhenyang on 2017/9/8. */@runwith(springrunner.class)@springboottestpublic class userproejctrepositorytest { @autowired @persistencecontext private entitymanager entitymanager; @autowired private userprojectrepository userprojectrepository; @test public void testuserprojectrepository(){ userprojectmultikeysclass userprojectmultikeysclass = new userprojectmultikeysclass(1, 1, "2017-09-08"); userproject userproject = entitymanager.find(userproject.class,userprojectmultikeysclass); system.out.println(userproject.tostring()); } @test public void testfindbyuserid(){ list<userproject> userprojects = userprojectrepository.findbyuserid(1); for(userproject userproject:userprojects){ system.out.println(userproject.tostring()); } } @test public void testfindbyprojectid(){ list<userproject> userprojects = userprojectrepository.findbyprojectid(1); for(userproject userproject:userprojects){ system.out.println(userproject.tostring()); } } @test public void testfindbyuseridandprojectid(){ list<userproject> userprojects = userprojectrepository.findbyuseridandprojectid(1,1); for(userproject userproject:userprojects){ system.out.println(userproject.tostring()); } }} |
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。
原文链接：https://blog.csdn.net/qq_35056292/article/details/77892012
