JPA添加子女記錄 - 父母有3個副本

Question

我有新聞實體和評論實體。我想用0條評論創建新聞，然後在此新聞中添加一些評論。

在數據庫我有新聞信息和news_id列在COMMENTS表中的新聞。

News.java：

@Entity 
@Table(name = "NEWS") 
public class News implements Serializable{ 
    /** 
    * serialVersionUID 
    */ 
    private static final long serialVersionUID = 883279937885116359L; 
    /** 
    * News id 
    */ 
    @Id 
    @GeneratedValue(generator = "seq") 
    @SequenceGenerator(name="seq", sequenceName="NEWS_SEQ",allocationSize=1) 
    @Column(name = "NEWS_ID", nullable = false, unique = true) 
    private Long id; 
    /** 
    * News short text 
    */ 
    @Column(name = "SHORT_TEXT") 
    private String shortText; 
    /** 
    * News full text 
    */ 
    @Column(name = "FULL_TEXT") 
    private String fullText; 
    /** 
    * News title 
    */ 
    @Column(name = "TITLE") 
    private String title; 
    /** 
    * News creation date 
    */ 
    @Column(name = "CREATION_DATE") 
    private Date creationDate; 
    /** 
    * News modification date 
    */ 
    /** 
    * News comments 
    */ 
    @OneToMany(cascade = CascadeType.ALL, orphanRemoval= true, fetch = FetchType.EAGER) 
    @JoinColumn(name = "NEWS_ID") 
    private List<Comment> comments; 

Comment.java：

@Entity 
@Table(name = "COMMENTS") 
public class Comment implements Serializable{ 
    /** 
    * serialVersionUID 
    */ 
    private static final long serialVersionUID = -5697896094322498108L; 
    /** 
    * Comment id 
    */ 
    @Id 
    @GeneratedValue(generator = "seq") 
    @SequenceGenerator(name="seq", sequenceName="COMMENTS_SEQ",allocationSize=1) 
    @Column(name = "COMMENT_ID", nullable = false, unique = true) 
    private Long id; 
    /** 
    * Comment text 
    */ 
    @Column(name = "COMMENT_TEXT") 
    private String commentText; 
    /** 
    * Comment creation date 
    */ 
    @Column(name = "CREATION_DATE") 
    private Date creationDate; 
    /** 
    * Id of the news which the comment is added to 
    */ 
    @Column(name = "NEWS_ID") 
    private Long newsId; 

我有這樣的代碼：

  News news = new News(); 

      news.setTitle("qwerty"); 
      news.setShortText("qwerty"); 
      news.setFullText("qwerty"); 

      jpaNewsDAO.add(news); 
      news = jpaNewsDAO.findById(news.getId());//everything is fine here 
                // 0 comments 
      Comment comment = new Comment(null,"qwerty",new Date(),news.getId()); 
      jpaCommentDAO.add(comment); 
      news = jpaNewsDAO.findById(news.getId()); 

但是news.comments後有3項與副本（即使有相同的ID）的評論，我不明白爲什麼。 DB中只有一個這樣的評論。

添加評論：

@Override 
    public Long add(Comment entity) throws DAOException { 
     EntityManager manager = null; 
     EntityTransaction transaction; 
     try { 
      manager = managerFactory.createEntityManager(); 
      transaction = manager.getTransaction(); 
      transaction.begin(); 
      entity.setId(null); 
      manager.persist(entity); 
      manager.flush(); 
      transaction.commit(); 
     } catch (PersistenceException e) { 
      throw new DAOException(e); 
     } finally { 
      closeManager(manager); 
     } 
     return entity.getId(); 
    } 

添加消息：

@Override 
    public Long add(News entity) throws DAOException { 
     EntityManager manager = null; 
     EntityTransaction transaction; 
     try { 
      manager = managerFactory.createEntityManager(); 
      transaction = manager.getTransaction(); 
      transaction.begin(); 
      entity.setId(null); 

      List<Comment> comments = new ArrayList<Comment>(); 
      if (entity.getComments()!= null) { 
       for (Comment comment : entity.getComments()) { 
        comments.add(manager.find(Comment.class, comment.getId())); 
       } 
      } 
      entity.setComments(comments); 

      manager.persist(entity);//add 
      manager.flush(); 
      transaction.commit(); 
     } catch (PersistenceException e) { 
      throw new DAOException(e); 
     } finally { 
      closeManager(manager); 
     } 
     return entity.getId(); 
    } 

那麼，爲什麼我有意見的副本？

Answer 1

問題是由於新聞和評論之間的關係標記爲EAGER。有關這是爲什麼更多信息的情況下在這裏看到：

Hibernate Criteria returns children multiple times with FetchType.EAGER

可以標記關係，懶惰，這將防止問題。通常情況下，最佳實踐是以這種方式定義關係，並通過查詢提示或JPA 2.1的新「實體圖」功能，按照給定用途的要求快速提取關係。

https://blogs.oracle.com/theaquarium/entry/jpa_2_1_entity_graphs

現在，你可以簡單地添加下面一行在你的DAO：

news.getComments（）大小（）。

這將強制延遲收集加載。它顯然將在您的Web層中可用。

Answer 2

移動事務開始/提交更高，並在其評論請確保您的新聞對象點，反之亦然

Transaction transaction = beginTransaction(); //start a transaction 
News news = new News();  
news.setTitle("qwerty"); 
news.setShortText("qwerty"); 
news.setFullText("qwerty"); 

Comment comment = new Comment(null,"qwerty",new Date(),news); //note news not news.getId() 

news.addComment(comment); 

//You now have a correct "graph" news points at comment and comment points at news 

//persist 
jpaNewsDAO.add(news); 

commitTransaction(transaction); //commit 

//Hibernate will now have persisted both Comment and News for you 

只添加依舊沒有別的需要處理異常你曾經認爲適合

@Override 
public Long add(News entity) throws DAOException { 

    manager.persist(entity); 
}