hibernate uuid.hex主键生成带来的困惑

<?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">
<!--
Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
<class name="org.feiying.hualong.vo.Housepic" table="housepic" catalog="hualong">
<id name="hpid" type="java.lang.Integer">
<column name="HPid" />
<generator class="native" />
</id>
<property name="picid" type="java.lang.String">
<column name="picid" length="32" unique="true" />
</property>
<property name="hppic" type="java.lang.String">
<column name="HPPic" length="200" />
</property>
<property name="hporder" type="java.lang.Integer">
<column name="HPOrder" />
</property>
<property name="filesize" type="java.lang.Double">
<column name="Filesize" precision="22" scale="0" />
</property>
<property name="uploadTime" type="java.util.Date">
<column name="UploadTime" length="19" />
</property>
<property name="isPic" type="java.lang.Integer">
<column name="IsPic" />
</property>
<property name="username" type="java.lang.String">
<column name="Username" length="45" />
</property>
</class>
</hibernate-mapping>


1。确认id字段在数据库是varchar(32)
2.表按id字段做索引