Hibernate入门

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　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>

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。