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我是新来的冬眠。我想在netbeans中使用 hibernate 在书籍和作者之间创建多对多的连接。我看到的所有示例都是针对 Eclipse 而我找不到我的问题的答案。我的 Book.hbm.xml 是：

<hibernate-mapping>
<class name="Book" table="books">
  <id name="bookId" type="int" column="BookID">
     <generator class="assigned"/>
  </id>
  <property name="isbn" column="Isbn" type="string"/>
  <property name="title" column="Title" type="string"/>
  <property name="bookPicPath" column="BookPicPath" type="string"/>
  <property name="summary" column="Summary" type="string"/>
  <property name="genry" column="Genry" type="string"/>
  <property name="parentGenry" column="ParentGenry" type="string"/>
  <set name="authors" table="Book_Author" cascade="all">
        <key column="BookID" />
        <many-to-many column="AuthorID"  class="Author" />
  </set>

</class>
</hibernate-mapping>

Author.hbm.xml 是：

<hibernate-mapping>
<class name="Author" table="authors">
  <id name="authorId" type="int" column="AuthorID">
     <generator class="assigned"/>
  </id>
  <property name="fname" column="Fname" type="string"/>
  <property name="lname" column="Lname" type="string"/>
  <property name="biography" column="Biography" type="string"/>
  <property name="gender" column="Gender" type="string"/>
  <property name="website" column="Website" type="string"/>
  <property name="authorPicPath" column="AuthorPicPath" type="string"/>
</class>
</hibernate-mapping>

在主类中，我创建这样的表：

HibernateUtil.droptable("drop table authors");
HibernateUtil.setup("create table authors ( AuthorID int, Fname VARCHAR(20), Lname VARCHAR(20), Biography VARCHAR(255), Gender VARCHAR(20), Website VARCHAR(255), AuthorPicPath VARCHAR(255))");
HibernateUtil.droptable("drop table books");
HibernateUtil.setup("create table books ( BookID int, Isbn VARCHAR(20), Title VARCHAR(255), BookPicPath VARCHAR(255), Summary VARCHAR(255), Genry VARCHAR(255), ParentGenry VARCHAR(255))");

我的问题：

1.在多对多关系中有一个连接表（Book_Author）。现在我必须手动完成还是hibernate自己创建？
2.在主课上我有：

SessionFactory sessions = new Configuration().configure().buildSessionFactory();
Session session = sessions.openSession();

    Transaction tx = null;
    try {
        tx = session.beginTransaction();

        Set<Author> authors = new HashSet<Author>();
        Author a1 = new Author("1","1","1","1","1","1");
        Author a2 = new Author("2","2","2","2","2","2");
        authors.add(a1);
        authors.add(a2);

        Book b1= new Book("a","a","a","a","a","a",authors);
        session.save(b1);

        tx.commit();
        tx = null;           

    } catch ( HibernateException e ) {
        if ( tx != null )
            tx.rollback();
            e.printStackTrace();

    } finally {
        session.close();
    }

但是当我运行程序时，我看到以下错误：

a different object with the same identifier value was already associated with the session: [Author#0]

请指导。谢谢。

4

1 回答 1

0

  1. 如果您使用 SchemaExport (aka hbm2ddl)，hibernate 可以自动Book_Author为您生成关系表 ()。您可以hibernate.cfg.xml像这样配置它：<property name="hibernate.hbm2ddl.auto">create-drop</property>

  2. 我看到你用<generator class="assigned"/>你的身份证。在这种情况下，您必须手动分配 id；如果你不这样做，休眠将抛出该异常。

于 2013-04-21T21:15:01.590 回答