The database returned no natively generated identity value

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.how2java.pojo">
<class name="Category" table="category_">
<id name="id" column="id">
<generator class="native">
</generator>
</id>
<property name="name" />

</class>

</hibernate-mapping>