Spring JPA复合主键实体更新时重复行异常解决方案咨询

问题 #

我正在开发一个基于Spring的REST API，支持用户注册漫画并对已注册的漫画进行评分。API核心功能之一是用户可为漫画打分，为此我创建了基于复合主键（用户+漫画）的JPA实体Rate存储评分数据，并编写了注册和修改评分的服务。但遇到问题：用户首次给某漫画评分时一切正常，尝试修改评分时抛出异常：

org.hibernate.HibernateException: Duplicate row was found and `ASSERT` was specified
    at org.hibernate.sql.results.spi.ListResultsConsumer.consume(ListResultsConsumer.java:187) ~[hibernate-core-6.2.6.Final.jar:6.2.6.Final]
    ...（省略后续栈信息）

相关代码如下：

RatePK #

@Embeddable
public class RatePK implements Serializable {
    private static final long serialVersionUID = 1L;
    
    @ManyToOne
    @JoinColumn(name="user_id")
    private User user;
    
    @ManyToOne
    @JoinColumn(name="comic_id")
    private Comic comic;

    public RatePK(User user, Comic comic) {
        this.user = user;
        this.comic = comic;
    }

    public User getUser() {
        return user;
    }

    public Comic getComic() {
        return comic;
    }

    public void setUser(User user) {
        this.user = user;
    }

    public void setComic(Comic comic) {
        this.comic = comic;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((comic == null) ? 0 : comic.hashCode());
        result = prime * result + ((user == null) ? 0 : user.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;
        RatePK other = (RatePK) obj;
        if (comic == null) {
            if (other.comic != null)
                return false;
        } else if (!comic.equals(other.comic))
            return false;
        if (user == null) {
            if (other.user != null)
                return false;
        } else if (!user.equals(other.user))
            return false;
        return true;
    }
    
}

Rate #

@Entity
@Table(name="TB_RATE")
public class Rate implements Serializable {
    private static final long serialVersionUID = 1L;
    
    @EmbeddedId
    private RatePK id = new RatePK();
    
    private Integer rate;

    public Rate(User user, Comic comic, Integer rate) {
        super();
        this.id.setUser(user);
        this.id.setComic(comic);
        this.rate = rate;
    }

    public RatePK getId() {
        return id;
    }

    public Integer getRate() {
        return rate;
    }

    public void setId(RatePK id) {
        this.id = id;
    }

    public void setRate(Integer rate) {
        this.rate = rate;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((id == null) ? 0 : id.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;
        Rate other = (Rate) obj;
        if (id == null) {
            if (other.id != null)
                return false;
        } else if (!id.equals(other.id))
            return false;
        return true;
    }
    
}

RateRepository #

@Repository
public interface RateRepository extends JpaRepository<Rate, RatePK> {

}

RateService #

public void save(Long comicId, RateNewDTO rateDto) {        
    UserSS userAuthenticated = UserService.authenticated(); 
        
    User user = userService.findById(userAuthenticated.getId());
        
    Comic comic = comicService.findById(comicId);
        
    Rate rate = new Rate(user, comic, rateDto.getRate());

    rateRepository.save(rate);  
}

解决方案 #

问题根源 #

每次修改评分时，你直接创建新的Rate对象调用save()方法，但JPA的save()逻辑是：若实体是未被持久化上下文管理的新实例，执行插入；若为已持久化的实例，才会执行更新。

用户再次评分时，新创建的Rate对象主键虽与数据库现有记录一致，但不在当前持久化上下文中，JPA会尝试插入重复主键的记录，触发重复行异常。

解决步骤 #

1. 先查询已有评分再处理
   保存前先通过复合主键查询是否存在该用户对该漫画的评分，存在则更新，不存在则新建。修改RateService的save方法：

   public void save(Long comicId, RateNewDTO rateDto) {        
       UserSS userAuthenticated = UserService.authenticated(); 
       User user = userService.findById(userAuthenticated.getId());
       Comic comic = comicService.findById(comicId);
       
       // 构建复合主键
       RatePK ratePK = new RatePK(user, comic);
       // 查询已有评分
       Optional<Rate> existingRate = rateRepository.findById(ratePK);
       
       Rate rate;
       if (existingRate.isPresent()) {
           // 存在则更新评分值
           rate = existingRate.get();
           rate.setRate(rateDto.getRate());
       } else {
           // 不存在则新建
           rate = new Rate(user, comic, rateDto.getRate());
       }
       
       rateRepository.save(rate);  
   }
   

2. 补充无参构造函数
   JPA要求实体类和可嵌入主键类必须有无参构造，否则查询实例化时可能出错。给RatePK和Rate添加：

   // RatePK中添加
   public RatePK() {}
   
   // Rate中添加
   public Rate() {}
   

3. 优化复合主键的equals/hashCode（可选但建议）
   当前RatePK的equals/hashCode依赖User和Comic对象的equals实现，若实体状态变化可能导致主键判断出错。建议改为依赖ID字段：

   @Embeddable
   public class RatePK implements Serializable {
       private static final long serialVersionUID = 1L;
       
       @Column(name="user_id")
       private Long userId;
       
       @Column(name="comic_id")
       private Long comicId;
   
       // 关联关系设为懒加载，且不参与插入更新
       @ManyToOne(fetch = FetchType.LAZY)
       @JoinColumn(name="user_id", insertable = false, updatable = false)
       private User user;
       
       @ManyToOne(fetch = FetchType.LAZY)
       @JoinColumn(name="comic_id", insertable = false, updatable = false)
       private Comic comic;
   
       public RatePK() {}
       
       public RatePK(Long userId, Long comicId) {
           this.userId = userId;
           this.comicId = comicId;
       }
   
       // getter、setter省略...
   
       @Override
       public int hashCode() {
           final int prime = 31;
           int result = 1;
           result = prime * result + ((comicId == null) ? 0 : comicId.hashCode());
           result = prime * result + ((userId == null) ? 0 : userId.hashCode());
           return result;
       }
   
       @Override
       public boolean equals(Object obj) {
           if (this == obj) return true;
           if (obj == null || getClass() != obj.getClass()) return false;
           RatePK other = (RatePK) obj;
           return Objects.equals(comicId, other.comicId) && Objects.equals(userId, other.userId);
       }
   }
   

   对应的Rate构造函数调整为：

   public Rate(User user, Comic comic, Integer rate) {
       this.id.setUserId(user.getId());
       this.id.setComicId(comic.getId());
       this.rate = rate;
   }
   

内容的提问来源于stack exchange，提问作者Gustavo Cruz