休眠选择一对多帮助

我有以下类映射为一对多：读者和书籍，当一个读者可以容纳一个以上的书：休眠选择一对多帮助

书：

@Entity 
@Table(name = "book") 
public class Book implements Serializable{ 

    private static final long serialVersionUID = 1L; 

    private Long id; 
    private String author; 
    private String title; 

    public Book(){} 
    public Book(String author,String title){ 
     this.author = author; 
     this.title = title; 
    } 

    @Id 
    @GeneratedValue 
    @Column(name = "BOOK_ID") 
    public Long getId() { 
     return id; 
    } 

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

    @Column(name = "author") 
    public String getAuthor() { 
     return author; 
    } 
    public void setAuthor(String author) { 
     this.author = author; 
    } 

    @Column(name="title") 
    public String getTitle() { 
     return title; 
    } 
    public void setTitle(String title) { 
     this.title = title; 
    } 
    //equals and hashcode ommited. 
}

读者

@Entity 
@Table(name = "reader") 
public class Reader implements Serializable{ 

    private static final long serialVersionUID = 1L; 

    private Long id; 
    private String firstName; 
    private String lastName; 
    Set<Book> set = new HashSet<Book>(); 

    @Transient 
    public void loanBook(Book book){ 
     set.add(book); 
    } 

    @Id 
    @GeneratedValue 
    @Column(name = "READER_ID") 
    public Long getId() { 
     return id; 
    } 

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

    @Column(name="firstName") 
    public String getFirstName() { 
     return firstName; 
    } 


    public void setFirstName(String firstName) { 
     this.firstName = firstName; 
    } 


    @Column(name="lastName") 
    public String getLastName() { 
     return lastName; 
    } 


    public void setLastName(String lastName) { 
     this.lastName = lastName; 
    } 

    @OneToMany(cascade=CascadeType.ALL,fetch = FetchType.LAZY) 
    @JoinColumn(name="READER_ID") 
    public Set<Book> getSet() { 
     return set; 
    } 


    public void setSet(Set<Book> set) { 
     this.set = set; 
    } 

    public Reader(){} 

    public Reader(String firstName, String lastName){ 
     this.firstName = firstName; 
     this.lastName = lastName; 
    } 
}

现在我想用一些书籍ID取读卡器类，例如：

Reader reader = service.getReaderbyBook(Long.valueOf(10));

我的功能看起来像：

@Override 
    public Reader getReaderbyBook(Long id) { 
     Session session = null; 
     Reader reader = null; 
     session =sessionFactory.openSession(); 
      org.hibernate.Transaction tr = session.getTransaction(); 
      tr.begin(); 
      String hqlSelect = "Select .... where book.id:=id"; 
      Query query = session.createQuery(hqlSelect); 
      query.setLong("id", id); 
      reader = (Reader) query.uniqueResult(); 
      tr.commit(); 
      session.flush(); 
       session.close(); 
       return reader; 
    } 

}

如何我的HQL选择应该是这样，如果我只是想获取一些书相关的单一阅读器？

来源

2011-03-23 danny.lesnik

from Reader r join r.set book where book.id = :id。

来源

2011-03-23 08:13:47 gkamal

-2

我认为你应该创建一张表来将读者映射到书本上。它使事情变得更容易。

来源

2011-03-23 08:21:09 Amanpreet

它的一对多 - 如何创建额外的表帮助？ – Nilesh 2011-03-23 08:26:34

@Nilesh：让我们假设你有一张表，主键为reader_id的读者，然后你有主表book_id的表书...现在添加另一个名为Issued_books_by_readers，并为读者添加reader_id和book_id。请记住，一旦图书被退回，请将其保存在历史记录表中，并删除表格中的记录。这是我认为你可以在数据库级别 – Amanpreet 2011-04-14 12:06:02

中处理1到多个这就是多对多！ – Nilesh 2011-04-14 13:10:25

休眠选择一对多帮助

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