Hibernate的数据删除，更改

　　　　　　　　　　　　　　　　　　　　　　其他未给出代码，请参考上一篇....

一.数据的删除

方法1.从“多”的一方进行数据的删除

books.hbm.xml文件不变：

<many-to-one name="publishers" column="publisherId" class="com.entry.Publishers" lazy="false"cascade="save-update"/>

publishers.hbm.xml文件：

<set name="books" lazy="false" cascade="all" inverse="true"> <!-- cascade="save-update" 也可以 --><key column="publisherId" not-null="true"/><one-to-many class="com.entry.Books"/></set>

在MyHibernateDao.java中添加如下代码：

public Books getBook(int Id){Books book = null;Session session = HibernateSessionFactory.getSession();Transaction tran = session.beginTransaction();book = (Books)session.get(Books.class, new Integer(Id));tran.commit();return book;}public void deleteBook(Books book){Session session = HibernateSessionFactory.getSession();Transaction tran = session.beginTransaction();session.delete(book);tran.commit();}

在HibernateServlet.java中添加如下代码

        Books book1 = dao.getBook(3);book1.getPublishers().getBooks().remove(book1);book1.setPublishers(null);dao.deleteBook(book1);

注意如果没有book1.getPublishers().getBooks().remove(book1); book1.setPublishers(null);这两句，会出现 org.hibernate.ObjectDeletedException: deleted object would be re-saved by cascade (remove deleted object from associations)这个异常，主要是因为Books和Publishers二者的级联关系。

所以我们可以先将级联断开，然后再进行删除“多”的一方。

方法2.从“一”的这一方进行删除，这样的话就是和“一”这一方相关联的“多”的一方都会被删除

在HibernateServlet.java中添加如下代码：

Publishers publisher = dao.getPublisher(1);
dao.deletePublisher(publisher);

publishers.hbm.xml 和 books.hbm.xml 不用改变

在MyHibernateDao.java中添加如下代码：

public Publishers getPublisher(int Id){Publishers publisher = null;Session session = HibernateSessionFactory.getSession();Transaction tran = session.beginTransaction();publisher = (Publishers)session.get(Publishers.class, new Integer(Id));tran.commit();return publisher;}public void deletePublisher(Publishers publisher){Session session = HibernateSessionFactory.getSession();Transaction tran = session.beginTransaction();session.delete(publisher);tran.commit();}

二.数据的删除

在MyHibernateDao.java中添加如下代码：

public void updateBooks(Books book){Session session = HibernateSessionFactory.getSession();Transaction tran = session.beginTransaction();session.update(book);tran.commit();}

在HibernateServlet.java中添加如下代码

　　　　　//更改数据， 更改对应的外键Books book1 = dao.getBook(79);//将book1的publisherId替换成46/较为安全的写法，然而并不知道有什么卵用Publishers px = dao.getPublisher(book1.getPublishers().getPublisherId());px.getBooks().remove(book1);Publishers py = dao.getPublisher(46);py.getBooks().add(book1);/
        book1.setPublishers(py);dao.updateBooks(book1);//更改数据，BooksBooks book2 = dao.getBook(79);book2.setTitle("如何成为成功的人士");dao.updateBooks(book2);