Spring Data Jpa 復(fù)合主鍵的實(shí)現(xiàn)

發(fā)布時(shí)間：2020-09-28 01:12:44 來(lái)源：腳本之家閱讀：232 作者：冬天飲雪水欄目：編程語(yǔ)言

前言

這次大創(chuàng)有個(gè)需求，在數(shù)據(jù)庫(kù)建表時(shí)發(fā)現(xiàn)，user表與project表的關(guān)系表 user_project的主鍵為復(fù)合主鍵：

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)
);

在網(wǎng)上看了幾篇博客，以及在spring boot干貨群咨詢（感謝夜升額耐心解答）過(guò)后總算是做出來(lái)了。這里做個(gè)總結(jié)，方便日后查閱。

正文

這里采用@IdClass注解的方式來(lái)實(shí)現(xiàn)復(fù)合主鍵；

思路

編寫(xiě)一個(gè)復(fù)合主鍵類UserProjectMultiKeysClass;
通過(guò)@IdClass注釋在實(shí)體中標(biāo)注復(fù)合主鍵;
可以通過(guò)EntityManager獲取數(shù)據(jù)，或者是直接在Repository 里寫(xiě)方法；

實(shí)現(xiàn)

復(fù)合主鍵類

package com.hzy.Model;

import java.io.Serializable;

/**
 * Created by huangzhenyang on 2017/9/7.
 * UserProject的復(fù)合主鍵類
 *
 * @Param userId
 * @Param projectId
 * @Param timestamp
 * 由這三個(gè)共同組成復(fù)合主鍵
 */
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;
  }

  // ***重寫(xiě)hashCode與equals方法*** 劃重點(diǎn)！
  @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：

復(fù)合主鍵類必須滿足：
1. 實(shí)現(xiàn)Serializable接口;
2. 有默認(rèn)的public無(wú)參數(shù)的構(gòu)造方法;
3. 重寫(xiě)equals和hashCode方法。equals方法用于判斷兩個(gè)對(duì)象是否相同，EntityManger通過(guò)find方法來(lái)查找Entity時(shí)，是根據(jù)equals的返回值來(lái)判斷的。hashCode方法返回當(dāng)前對(duì)象的哈希碼;

實(shí)體類

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標(biāo)注用于標(biāo)注實(shí)體所使用主鍵規(guī)則的類；
2. 在實(shí)體中同時(shí)標(biāo)注主鍵的屬性，比如這段代碼中的userId,projectId以及timestamp ；

獲取數(shù)據(jù)

方法一：通過(guò)EntityManager獲取，比如方法testUserProjectRepository()

方法二：通過(guò)Repository獲取；這里記得在extends JpaRepository<UserProject,UserProjectMultiKeysClass>時(shí)把id的主鍵類指定為復(fù)合主鍵類UserProjectMultiKeysClass

public interface UserProjectRepository extends JpaRepository<UserProject,UserProjectMultiKeysClass>{
  // 根據(jù)用戶Id,找出用戶參與的所有UserProject
  // TEST PASS
  List<UserProject> findByUserId(Integer userId);

  // 根據(jù)項(xiàng)目id,找出參與項(xiàng)目的所有UserProject
  // TEST PASS
  List<UserProject> findByProjectId(Integer projectId);

  // 根據(jù)用戶id和項(xiàng)目id 找出所有的UserProject
  // TEST PASS
  List<UserProject> findByUserIdAndProjectId(Integer userId,Integer projectId);
}

單元測(cè)試的代碼

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());
    }
  }
}

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Spring Data Jpa 復(fù)合主鍵的實(shí)現(xiàn)

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