乖乖，hibernate 居然会这样？？Why?
1。表名：tUser1
CREATE TABLE [dbo].[tUser1] (
[uid] [int] NOT NULL ,
[username] [varchar] (255) COLLATE Chinese_PRC_CI_AS NULL ,
[password] [varchar] (255) COLLATE Chinese_PRC_CI_AS NULL
) ON [PRIMARY]
GO
2。User.hbm.xml
<?xml version= "1.0 " encoding= "UTF-8 "?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN "
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd ">
<hibernate-mapping>
<class name= "com.hibernate.User " table= "tUser1 ">
<id name= "uid " column= "uid " type= "java.lang.Integer ">
<generator class= "increment "/>
</id>
<property name= "username "/>
<property name= "password "/>
</class>
</hibernate-mapping>
3.class: HibernateUtil
package com.hibernate;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HibernateUtil {
private static final SessionFactory sessionFactory;
static{
try{
sessionFactory=new Configuration().configure().buildSessionFactory();
}catch(Throwable ex){
throw new ExceptionInInitializerError(ex);
}
}
public static final ThreadLocal session=new ThreadLocal();
public static SessioncurrentSession()throws HibernateException{
Session s=(Session)session.get();
if(s==null){
s=sessionFactory.openSession();
session.set(s);
}
return s;
}
public static void closeSession()throws HibernateException{
Session s=(Session)session.get();
session.set( null);
if(s!=null){
s.close();
}
}
}
4 测试类 test.java
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
public class Test {
public static void main(String args[]){
try{
Session session=HibernateUtil.currentSession();
Transaction tx=session.beginTransaction();
User user=new User();
user.setUsername( "中国 ");
user.setPassword( "123 ");
session.save(user);
tx.commit();
session.close();
}catch(HibernateException e){
e.printStackTrace();
}
}
}
问题：表 tUser1中原来有几条数据，运行test.java 可以将数据插入 tUser1 中，但原来的数据被删掉了。为什么呢？如果再次运行，表中还是只有一条数据
1 中国 123
运行两次的话不应该是
1 中国 123
2 中国 123
吗？
[解决办法]
ID 产生器的问题吧~~~
<generator class= "increment "/>
对数据库的依赖性比较大, 对不同的数据库会产生不同的结果.
建议换成 native , 由hibernate依据数据库来建立.
或者换成 assigned, 创建自己的ID产生器.
[解决办法]
数据库id要设位自增，之后hbm.xml的id要定义unsaved-value，一般为unsaved-value= "null "，之后运行，看看Hibernate输出的SQL.
