jsp Hibernate入门教程

2008-11-14 23:08:55 作者：

如果您是在同一个Session中取出数据并想要马上进行更新，则只要先查询并取出对象，透过setXXX()方法设定好新的值，然后呼叫session.flush()即可在同一个Session中更新指定的数据

例如：

HibernateTest.java 
import onlyfun.caterpillar.*; 
import net.sf.hibernate.*; 
import net.sf.hibernate.cfg.*; 
import java.util.*; 
public class HibernateTest { 
public static void main(String[] args) throws HibernateException { 
SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory(); 
Session session = sessionFactory.openSession(); 
List users = session.find("from User"); 
User updated = null; 
for (ListIterator iterator = users.listIterator(); iterator.hasNext(); ) { 
User user = (User) iterator.next(); 
if(updated == null) 
updated = user; 
System.out.println(user.getName() + 
"\n\tAge: " + user.getAge() + 
"\n\tSex: " + user.getSex()); 
} 
updated.setName("justin"); 
session.flush(); 
users = session.find("from User"); 
session.close(); 
sessionFactory.close(); 
for (ListIterator iterator = users.listIterator(); iterator.hasNext(); ) { 
User user = (User) iterator.next(); 
System.out.println(user.getName() + 
"\n\tAge: " + user.getAge() + 
"\n\tSex: " + user.getSex()); 
} 
} 
} 

　这个程序会显示数据表中的所有数据，并将数据表中的第一笔数据更新，一个执行的结果如下：
log4j:WARN No appenders could be found for logger (net.sf.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Hibernate: select user0_.user_id as user_id, user0_.name as name, user0_.sex as sex, user0_.age as age from USER user0_
caterpillar
Age: 28
Sex: M
momor
Age: 25
Sex: F
Bush
Age: 25
Sex: M
Becky
Age: 35
Sex: F
Hibernate: update USER set name=?, sex=?, age=? where user_id=?
Hibernate: select user0_.user_id as user_id, user0_.name as name, user0_.sex as sex, user0_.age as age from USER user0_
justin
Age: 28
Sex: M
momor
Age: 25
Sex: F
Bush
Age: 25
Sex: M
Becky
Age: 35
Sex: F

　如果您开启了一个Session，从数据表中取出数据显示到使用者接口上，之后关闭Session，当使用者在接口上操作完毕并按下储存时，这时您要重新开启一个Session，使用update()方法将对象中的数据更新至对应的数据表中，一个例子如下：

复制代码代码如下:

HibernateTest.java 
import onlyfun.caterpillar.*; 
import net.sf.hibernate.*; 
import net.sf.hibernate.cfg.*; 
import java.util.*; 
public class HibernateTest { 
public static void main(String[] args) throws HibernateException { 
SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory(); 
Session session = sessionFactory.openSession(); 
List users = session.find("from User"); 
// 关闭这个Session 
session.close(); 
User updated = null; 
for (ListIterator iterator = users.listIterator(); iterator.hasNext(); ) { 
User user = (User) iterator.next(); 
if(updated == null) 
updated = user; 
System.out.println(user.getName() + 
"\n\tAge: " + user.getAge() + 
"\n\tSex: " + user.getSex()); 
} 
// 使用者作一些操作，之后储存 
updated.setName("caterpillar"); 
// 开启一个新的Session 
session = sessionFactory.openSession(); 
// 更新数据 
session.update(updated); 
users = session.find("from User"); 
session.close(); 
sessionFactory.close(); 
for (ListIterator iterator = users.listIterator(); iterator.hasNext(); ) { 
User user = (User) iterator.next(); 
System.out.println(user.getName() + 
"\n\tAge: " + user.getAge() + 
"\n\tSex: " + user.getSex()); 
} 
} 
}

　这个程序执行的结果范例如下，您可以看看实际上执行了哪些SQL：
log4j:WARN No appenders could be found for logger (net.sf.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Hibernate: select user0_.user_id as user_id, user0_.name as name, user0_.sex as sex, user0_.age as age from USER user0_
justin
Age: 28
Sex: M
momor
Age: 25
Sex: F
Bush
Age: 25
Sex: M
Becky
Age: 35
Sex: F
Hibernate: update USER set name=?, sex=?, age=? where user_id=?
Hibernate: select user0_.user_id as user_id, user0_.name as name, user0_.sex as sex, user0_.age as age from USER user0_
caterpillar
Age: 28
Sex: M
momor
Age: 25
Sex: F
Bush
Age: 25
Sex: M
Becky
Age: 35
Sex: F

　Hibernate提供了一个saveOrUpdate()方法，为数据的储存或更新提供了一个统一的操作接口，藉由定义映像文件时，设定<id>标签的unsaved-value来决定什么是新的值必需，什么是已有的值必须更新：
User.hbm.xml

复制代码代码如下:

<id name="id" type="string" unsaved-value="null"> 
<column name="user_id" sql-type="char(32)" /> 
<generator class="uuid.hex"/> 
</id> 

unsaved-value
可以设定的值包括：
any - 总是储存
none - 总是更新
null - id为null时储存（预设）
valid - id为null或是指定值时储存
　这样设定之后，您可以使用session.saveOrUpdate(updated);来取代上一个程序的session.update(updated);方法。
　如果要删除数据，只要使用delete()方法即可，直接看个例子。

复制代码代码如下:

HibernateTest.java 
import onlyfun.caterpillar.*; 
import net.sf.hibernate.*; 
import net.sf.hibernate.cfg.*; 
import java.util.*; 
public class HibernateTest { 
public static void main(String[] args) throws HibernateException { 
SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory(); 
Session session = sessionFactory.openSession(); 
List users = session.find("from User"); 
User updated = null; 
for (ListIterator iterator = users.listIterator(); iterator.hasNext(); ) { 
User user = (User) iterator.next(); 
if(updated == null) 
updated = user; 
System.out.println(user.getName() + 
"\n\tAge: " + user.getAge() + 
"\n\tSex: " + user.getSex()); 
} 
session.delete(updated); 
users = session.find("from User"); 
session.close(); 
sessionFactory.close(); 
for (ListIterator iterator = users.listIterator(); iterator.hasNext(); ) { 
User user = (User) iterator.next(); 
System.out.println(user.getName() + 
"\n\tAge: " + user.getAge() + 
"\n\tSex: " + user.getSex()); 
} 
} 
} 

　一个执行的结果范例如下：
log4j:WARN No appenders could be found for logger (net.sf.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Hibernate: select user0_.user_id as user_id, user0_.name as name, user0_.sex as sex, user0_.age as age from USER user0_
justin
Age: 28
Sex: M
momor
Age: 25
Sex: F
Bush
Age: 25
Sex: M
Becky
Age: 35
Sex: F
Hibernate: delete from USER where user_id=?
Hibernate: select user0_.user_id as user_id, user0_.name as name, user0_.sex as sex, user0_.age as age from USER user0_
momor
Age: 25
Sex: F
Bush
Age: 25
Sex: M
Becky
Age: 35
Sex: F
　Hibernate对于数据的更新、删除等动作，是依懒id值来判定，如果您已知id值，则可以使用load()方法来加载资料，例如：
User user = (User) session.load(User.class, id);
　更多有关于Hibernate资料更新操作的说明，您可以看看参考手册的第九章内容。

jsp Hibernate入门教程

您可能感兴趣的文章: