Question

我有点坚持在休眠中执行一对多的关系，所以需要一些关于我哪里出错的建议

作者类

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;
}

}

书类

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;
}
}

我的主要课程

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();

}
}

我收到此错误

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)

我想创建从作者到书的一对多映射，因为一个作者可以写很多书谁能解释我哪里出错了它会给你很大的帮助谢谢你

Answer 1

@OneToMany元素必须是Collection。所以而不是：

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

使用：

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

Set确保只存在唯一的Book（基于您的equals()实施）。如果不需要，您可以使用List<Book>。

此外，当您尝试向Author添加两本书时，您首先添加一本书，然后使用下一本书覆盖它：

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

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

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

此处，请改用books.add(book)。

Answer 2

这是不可能的。作者中的book字段应为集合，集合：

private Set<Book> books;

您还应该相应地更改setter和getter。另请注意字段名称：books。

查询关于hibernate中的一对多关系

2 个答案: