Need help with Hibernate? Read this first:
http://www.hibernate.org/ForumMailingli ... AskForHelp

Hibernate version:
3.0

Mapping documents:
<class name="com.abc.performance.UserAppraisalData" table="USER_APPRAISAL_RESPONSES" lazy="false">
<id column="ID" name="id" type="long" unsaved-value="null">
<generator class="hilo"/>
</id>
<discriminator column="RESPONSE_TYPE" type="string"/>
<timestamp column="LAST_MODIFIED_TS" name="lastModifiedTS"/>
<many-to-one name="user" class="com.abc.security.User" column="USER_ID" not-null="true" outer-join="true" lazy="true"/>
<many-to-one name="appraisal" class="com.abc.performance.PerformanceAppraisal" column="APPRAISAL_ID" not-null="true" lazy="false"/>
<many-to-one name="status" class="com.abc.performance.WorkflowStep" column="STATUS_ID" not-null="true" lazy="false"/>
<property column="SECTION_ID" length="10" name="pageSectionId" type="long"/>
<subclass name="com.abc.performance.UserAppraisalCart" discriminator-value="UserAppraisalCart" lazy="false">
<property column="RESPONSE_WEIGHT" length="10" name="inCart" type="long"/>
<many-to-one name="section" class="com.abc.performance.ReviewTemplatePageSection" column="RESPONSE_ID" outer-join="false" not-null="true" lazy="true"/>
<property column="RESPONSE_ID" length="10" name="sectionId" type="long" insert="false" update="false"/>
<property column="GOAL_COMP_ID" length="10" name="goalCompId" type="long"/>
</subclass>

<subclass name="com.abc.performance.UserAppraisalSignature" discriminator-value="UserAppraisalSignature" lazy="false">
<property column="RESPONSE_VALUE" length="50" name="signature" type="string"/>
</subclass>

<subclass name="com.abc.performance.UserAppraisalRating" discriminator-value="UserAppraisalRating" lazy="false">
<many-to-one name="formula" class="com.abc.performance.Formula" column="RESPONSE_ID" not-null="true" outer-join="false" lazy="false"/>
<property column="RESPONSE_WEIGHT" length="10" not-null="true" name="ratingValue" type="double"/>
<property column="RESPONSE_ID" length="10" name="formulaId" type="long" insert="false" update="false"/>
</subclass>

<subclass name="com.abc.performance.ManagerSelectedCompetency" discriminator-value="ManagerSelectedCompetency" lazy="false">
<many-to-one name="section" class="com.abc.performance.ReviewTemplatePageSection" column="RESPONSE_ID" outer-join="false" not-null="true" lazy="true"/>
<set name="managerCompetencies" table="KCT_SECTION_MANAGER_COMPETENCY" lazy="false">
<key column="SECTION_ID"/>
<many-to-many class="com.abc.common.Competency" column="COMPETENCY_ID"/>
</set>
</subclass>

<subclass name="com.abc.performance.UserResponse" discriminator-value="UserResponse" lazy="false">
<property column="GOAL_COMP_ID" length="10" name="goalCompId" type="long"/>
<property column="IS_ADHOC_RESPONSE" length="1" name="isAdhocResponse" not-null="true" type="true_false"/>
<many-to-one name="response" class="com.abc.performance.SectionResponse" column="RESPONSE_ID" not-null="true" outer-join="false" lazy="false"/>
<property column="RESPONSE_ID" length="10" name="responseId" type="long" insert="false" update="false"/>
<subclass name="com.abc.performance.UserAppraisalResponse" discriminator-value="UserAppraisalResponse" lazy="false">
<property column="RESPONSE_VALUE" length="500" name="responseValue" type="string"/>
<set name="ratingValues" inverse="true" outer-join="true" cascade="all-delete-orphan" lazy="true">
<key column="USER_APPRAISAL_RESPONSE_ID"/>
<one-to-many class="com.abc.performance.UserResponseRatingValue"/>
</set>
</subclass>

<subclass name="com.abc.performance.UserAppraisalResponseWeight" discriminator-value="UserAppraisalResponseWeight" lazy="false">
<property column="RESPONSE_WEIGHT" length="10" not-null="true" name="responseWeight" type="long"/>
</subclass>
</subclass>
</class>

Code between sessionFactory.openSession() and session.close():

Full stack trace of any exception that occurs:

Name and version of the database you are using:
ORACLE 9i

The generated SQL (show_sql=true):

Debug level Hibernate log excerpt:

I am randomly getting

cannot insert NULL into ("TEST"."USER_APPRAISAL_RESPONSES"."ID")

I think this occur because you defined the id to be of type "long" which in Java is a primitive. In this case, a non-saved value could be 0 but not null.
If you need it to be null you should consider to define it as "Long". This way, Java can make it null.

Thanks for the reply..

if that's the case, i should get error every time, but i am getting error ramdomly..