入門 07 - 更新,刪除資料My Window,Your Bridge!

入門 07 - 更新,刪除資料

2004-11-14 11:15:45

如果您是在同一個Session中取出資料並想要馬上進行更新，

則只要先查詢並取出物件，透過setXXX()方法設定好新的值，然後呼叫session.flush()即可在同一個Session中更新指定的資料，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());
}
}
}

　這個程式會顯示資料表中的所有資料，並將資料表中的第一筆資料更新，一個執行的結果如下：

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

　如果您開啟了一個Session，從資料表中取出資料顯示到使用者介面上，之後關閉Session，當使用者在介面上操作完畢並按下儲存時，這時您要重新開啟一個Session，使用update()方法將物件中的資料更新至對應的資料表中，一個例子如下：

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");
// 關閉這個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，之後儲存
updated.setName("caterpillar");

// 開啟一個新的Session
session = sessionFactory.openSession();
// 更新資料
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());
}
}
}

　這個程式執行的結果範例如下，您可以看看實際上執行了哪些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提供了一個saveOrUpdate()方法，為資料的儲存或更新提供了一個統一的操作介面，藉由定義映射文件時，設定<id>標籤的unsaved-value來決定什麼是新的值必需，什麼是已有的值必須更新：

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

可以設定的值包括：

any - 總是儲存
none - 總是更新
null - id為null時儲存（預設）
valid - id為null或是指定值時儲存

　這樣設定之後，您可以使用session.saveOrUpdate(updated);來取代上一個程式的session.update(updated);方法。
　如果要刪除資料，只要使用delete()方法即可，直接看個例子。

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());
}
}
}

　一個執行的結果範例如下：

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對於資料的更新、刪除等動作，是依懶id值來判定，如果您已知id值，則可以使用load()方法來載入資料，例如：

User user = (User) session.load(User.class, id);

　更多有關於Hibernate資料更新操作的說明，您可以看看參考手冊的第九章內容。

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入門 07 - 更新,刪除資料