Hibernate入门之更新,删除数据

　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：
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
<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。
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。