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"/>

<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>

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();
    }

 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();
    }

//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，Books
        Books book2 = dao.getBook(79);
        book2.setTitle("如何成为成功的人士");
        dao.updateBooks(book2);