Question

我想创建简单的网络应用程序，其中包含主题和评论。主题模型：

@Entity
@Table(name = "T_TOPIC")
public class Topic {
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private int id;

    @ManyToOne
    @JoinColumn(name="USER_ID")
    private User author;

    @Enumerated(EnumType.STRING)    
    private Tag topicTag;

    private String name;
    private String text;

    @OneToMany(fetch = FetchType.EAGER, mappedBy = "topic", cascade = CascadeType.ALL)
    private List<Comment> comments;

    // We shouldn't read whole collection to get this basic info
    private int commentsCount;
    private Date timeLastUpdated;

     /**
     * Removes comment from the Topic entity
     * @param comment
     */
     public void removeComment(Comment comment) {
            // updating topic
            timeLastUpdated = Utils.getCurrentTime();
            commentsCount--;
            comments.remove(comment);

     }
}

评论模型：

@Entity
@Table(name = "T_COMMENT")
public class Comment
{
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private int id;

    @ManyToOne
    @JoinColumn(name="TOPIC_ID")
    private Topic topic;

    @ManyToOne
    @JoinColumn(name="USER_ID")
    private User author;

    private String text;
    private Date creationDate;
}

评论服务：

@Service
@Transactional
public class CommentService {

    @Autowired
    private CommentRepository commentRepository;

    public int saveComment(Comment comment){
         return commentRepository.save(comment).getId();

    }   

    public Comment findCommentByID(int id){
        return commentRepository.findOne(id);
    }

     /**
     * Deletes a comment
     * @param comment -- a comment to delete
     * @return id of a topic
     */
     public int deleteComment(Comment comment) {
         int result = comment.getTopic().getId();
         commentRepository.delete(comment);
         return result;
     }
}

控制器的方法，即删除注释：

@RequestMapping(value = "/deleteComment/{commentId}", method = {RequestMethod.POST, RequestMethod.GET} )
public String deleteComment(@PathVariable int commentId, @ModelAttribute("comment")Comment comment, BindingResult result, Model model){
    Topic parentTopic;
    Comment deletedComment = commentService.findCommentByID(commentId);
    if (deletedComment != null) {
         // remove any relations
         parentTopic = deletedComment.getTopic();
         parentTopic.removeComment(deletedComment);
         // rempve the comment itself
         commentService.deleteComment(deletedComment);
        }
         //return "refresh:";
         return "home";
}

删除的实体传递给persist：[com.epam.mvc3.model.Comment＃]

Answer 1

如果您从存储库中删除它，则不必自己从Topic中的集合中删除Comment对象，并且我认为这样做会导致您的合并删除注释，并且删除以尝试删除并已删除评论。

尝试更改它以从主题中删除评论，然后保存主题。或者在运行查询的服务中创建一个方法，以计算给定主题的注释数量，而无需读取整个集合。

虽然评论提取类型非常渴望，但为什么不使用comments.size()？

Answer 2

按如下所示更改您的deleteComment（），

public int deleteComment(int commentId) 
{

         Comment existingComment = findCommentByID(commentId);
         if(existingComment != null)
         {

             int result = existingComment .getTopic().getId();
             Topic existingTopic = existingComment .getTopic();
             existingTopic.remove(existingComment) 
             topicRepository.save(existingTopic);// spring 3.1
             topicRepository.merge(existingTopic);// spring 3.0
             return result;

          }

       return 0;

     }

这里的要点是我们需要始终使用父dao / repository来处理子进程。

因此，首先从主题中删除注释，然后使用topicRepository保存/合并主题。

为什么'删除实体传递给持久'异常被提出？

2 个答案: