Spring Data Jpa 复合主键的实现

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

1. 编写一个复合主键类userprojectmultikeysclass;
2. 通过@idclass注释在实体中标注复合主键;
3. 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服务器之家。

原文链接：https://blog.csdn.net/qq_35056292/article/details/77892012