Spring Data Jpa 复合主键

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。

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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 ；

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获取数据

1. 方法一： 通过EntityManager获取，比如方法testUserProjectRepository()
2. 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)@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());        }    }}