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小牛知识库。