對於一個在休眠

IM還挺停留在執行一個在休眠一對多關係多對多關係查詢，所以需要一些建議，以在那裏我去錯了對於一個在休眠

Author類

package com.hibernate.arjun3; 

import javax.persistence.*; 

@Entity 
public class Author { 

private String name; 
@Id 
@GeneratedValue 
private int author_id; 

@OneToMany(cascade=CascadeType.ALL) 
private Book book; 

public Book getBook() { 
    return book; 
} 

public void setBook(Book book) { 
    this.book = book; 
} 

public String getName() { 
    return name; 
} 

public void setName(String name) { 
    this.name = name; 
} 

public int getAuthor_id() { 
    return author_id; 
} 

public void setAuthor_id(int author_id) { 
    this.author_id = author_id; 
} 

}

Book類

package com.hibernate.arjun3; 

import javax.persistence.*; 


@Entity 
public class Book { 

private String title; 

@Id 
@GeneratedValue 
private int author_id; 

public String getTitle() { 
    return title; 
} 

public void setTitle(String title) { 
    this.title = title; 
} 

public int getAuthor_id() { 
    return author_id; 
} 

public void setAuthor_id(int author_id) { 
    this.author_id = author_id; 
} 
}

我的主類

package com.hibernate.arjun3; 

import org.hibernate.Session; 
import org.hibernate.SessionFactory; 
import org.hibernate.cfg.AnnotationConfiguration; 

public class Main { 

public static void main(String args[]) { 

    Author author = new Author(); 
    author.setName("Brian"); 

    Book book = new Book(); 
    book.setTitle("The Incredible Brian"); 

    Book book2 = new Book(); 
    book2.setTitle("Superman"); 

    author.setBook(book); 
    author.setBook(book2); 


    SessionFactory factory = new AnnotationConfiguration().configure().buildSessionFactory(); 
    Session session = factory.openSession(); 
    session.beginTransaction(); 

    session.save(author); 

    session.getTransaction().commit(); 
    session.close(); 
    factory.close(); 

} 
}

，並即時得到這個錯誤

Exception in thread "main" org.hibernate.AnnotationException: Illegal attempt to map a non collection as a @OneToMany, @ManyToMany or @CollectionOfElements: com.hibernate.arjun3.Author.book 
    at org.hibernate.cfg.annotations.CollectionBinder.getCollectionBinder(CollectionBinder.java:330) 
    at org.hibernate.cfg.AnnotationBinder.processElementAnnotations(AnnotationBinder.java:1919) 
    at org.hibernate.cfg.AnnotationBinder.processIdPropertiesIfNotAlready(AnnotationBinder.java:963) 
    at org.hibernate.cfg.AnnotationBinder.bindClass(AnnotationBinder.java:796) 
    at org.hibernate.cfg.Configuration$MetadataSourceQueue.processAnnotatedClassesQueue(Configuration.java:3788) 
    at org.hibernate.cfg.Configuration$MetadataSourceQueue.processMetadata(Configuration.java:3742) 
    at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1410) 
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1844) 
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1928) 
    at com.hibernate.arjun3.MainAB.main(MainAB.java:24)

我想從筆者本書作爲一個作者可以寫很多書有人可以解釋我在哪裏，我去錯了它WLD有很大的創建一對多映射幫助感謝你

來源

2014-09-26 arjun narahari

@OneToMany元素必須是Collection。因此，而不是：

@OneToMany(cascade=CascadeType.ALL) 
private Book book;

用途：

@OneToMany(cascade=CascadeType.ALL) 
private Set<Book> books;

的Set確保只有唯一Book S能夠存在（根據您的equals()實現）。如果不需要，可以使用List<Book>。

此外，當您嘗試兩本書添加到Author，你是第一個加入，然後接着將其覆蓋：

Book book = new Book(); 
book.setTitle("The Incredible Brian"); 

Book book2 = new Book(); 
book2.setTitle("Superman"); 

author.setBook(book); 
author.setBook(book2);

在這裏，使用代替。

來源

2014-09-26 12:47:49 Magnilex

thanx很多bt你可以告訴我，我使用多對一的y沒有顯示相同的錯誤，y它顯示我使用一對多？ – 2014-09-26 13:26:38

@arjunnarahari你真的應該閱讀關於JPA的教程。如果作者有很多書，當然它需要是一個集合。 – Magnilex 2014-09-26 13:47:23

這是直截了當的。在筆者book場應該是一個集合，一組：

private Set<Book> books;

你也應該改變setter和getter相應爲好。還請注意字段名稱：books。

來源

2014-09-26 12:49:07

對於一個在休眠

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