Spring Data Jpa 复合主键的实现

上山打老虎

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：

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

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

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

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

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)
@springboottest
public 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CodeAE代码之家。
原文链接：https://blog.csdn.net/qq_35056292/article/details/77892012