hibernate插入新记录会覆盖mysql的旧记录
我做的一个简单的hibernate应用，照着例子做的，结果是每插入一条新记录，就将上一次插入的记录覆盖了．发下附上我的代码，请大家帮忙．

//Mysql   DB
DROP   TABLE   person;

CREATE   TABLE   person
(
id   varchar(32)   not   null   primary   key,
name   varchar(20)   not   null,
password   varchar(20)   not   null,
sex   varchar(2),
email   varchar(30)
);

//hibernate.cfg.xml
<?xml   version= '1.0 '   encoding= 'utf-8 '?>
<!DOCTYPE   hibernate-configuration   PUBLIC
"-//Hibernate/Hibernate   Configuration   DTD   3.0//EN "
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd ">

<hibernate-configuration>
<session-factory>
<property   name= "connection.driver_class "> com.mysql.jdbc.Driver </property>
<property   name= "connection.url "> jdbc:mysql://localhost/sunpool </property>
<property   name= "connection.username "> root </property>
<property   name= "connection.password "> root </property>
<property   name= "connection.pool_size "> 10 </property>
<property   name= "dialect "> org.hibernate.dialect.MySQL5Dialect </property>
<property   name= "current_session_context_class "> thread </property>
<property   name= "cache.provider_class "> org.hibernate.cache.NoCacheProvider </property>
<property   name= "show_sql "> true </property>
<property   name= "hbm2ddl.auto "> create </property>

<mapping   resource= "model/service/dao/Person.hbm.xml "   />
<mapping   resource= "model/service/dto/User.hbm.xml "   />

</session-factory>
</hibernate-configuration>

//person.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= "model.service.dao.Person "   table= "person ">
<id   name= "id "   column= "id "   type= "string ">
<generator   class= "uuid.hex "   />
</id>
<property   name= "name "   column= "name "   type= "string "   not-null= "true "   />
<property   name= "password "   column= "password "   type= "string "   not-null= "true "   />
<property   name= "sex "   column= "sex "   type= "string "   />
<property   name= "email "   column= "email "   type= "string "   />
</class>
</hibernate-mapping>

//PersonOperate.java
package   model.service.dao;

import   org.hibernate.Session;
import   org.hibernate.SessionFactory;
import   org.hibernate.Transaction;