I have a Parent Object P and a Child object Q,
When I am loading an parent object, hibernate issues delete and insert sql for child object, why does hibernate treat this as a insert and delte?

I don't believe you;-). Show me your mappings, java code and Hibernate output.

Justin

This happens sporadically with different data, also note while loading jobposting object only for qual child object insert and delte sql is executed but not for parent object and not for another child costcenterset.

I have seen similar insert and delete problem many times when a boolean field has null value.
In this case when qualCategoryId which is of string type had null value,
when I manually updated the db with some value the load seems to work and it called insert and delete on qual object.

Even if there is something wrong with the mapping or with object, why would hibernate execute insert/delte, this is totally weird.

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<!--
2003-12-17 Modified CustomField from Map to Set Mapping - Suresh
-->

<hibernate-mapping>

<class
name="insite.business.domain.cwm.JobPosting"
table="job_posting"
discriminator-value="0"
dynamic-insert="true"
dynamic-update="true">

<id name="id" type="string" column="job_posting_id">
<generator class="assigned"/>
</id>

<property name="requisitionId" type="string" column="requisition_id" not-null="true" length="14"/>
<property name="jobTemplateId" type="string" column="job_template_id" not-null="true" length="24"/>
<property name="ownerId" type="string" column="owner_id" not-null="true" length="24"/>
<property name="creatorId" type="string" column="creator_id" not-null="true" length="24"/>
<property name="buyerCode" type="string" column="buyer_code" not-null="true" length="4"/>
<property name="buId" type="string" column="bu_id" not-null="true" length="24"/>
<property name="externalRef" type="string" column="external_ref" length="100"/>
<property name="distributionListId" type="string" column="distribution_list_id" length="24"/>
<property name="coordinatorId" type="string" column="coordinator_id" length="24"/>
<property name="distributorId" type="string" column="distributor_id" length="24"/>
<property name="respondByDate" type="timestamp" column="respond_by_date" length="23"/>
<property name="distrTime" type="timestamp" column="distr_time" length="23"/>
<property name="positionsAvailable" type="integer" column="positions_available" not-null="true" length="10"/>
<property name="positionsFilled" type="integer" column="positions_filled" length="5"/>
<property name="comments" type="string" column="comments" length="1000"/>
<property name="title" type="string" column="title" not-null="true" length="100"/>
<property name="description" type="string" column="description" length="1000"/>
<property name="travelPct" type="big_decimal" column="travel_pct" length="9"/>
<property name="siteId" type="string" column="site_id" not-null="true" length="24"/>
<property name="hoursPerWeek" type="big_decimal" column="hours_per_week" length="13"/>
<property name="startDate" type="timestamp" column="start_date" not-null="true" length="23"/>
<property name="endDate" type="timestamp" column="end_date" not-null="true" length="23"/>
<property name="estOvertimePct" type="big_decimal" column="est_overtime_pct" length="9"/>
<property name="estExpensePct" type="big_decimal" column="est_expense_pct" length="9"/>
<property name="estSpend" type="big_decimal" column="est_spend" length="19"/>
<property name="currentDistributionLevel" type="integer" column="current_distribution_level" length="10"/>
<property name="maxDistributionLevel" type="integer" column="max_distribution_level" length="10"/>
<property name="lastDistrTime" type="timestamp" column="last_distr_time" length="23"/>
<property name="distributionPauseFlag" type="boolean" column="distribution_pause_flag" length="1"/>
<property name="distributionType" type="integer" column="distribution_type" not-null="true" length="10"/>
<property name="activeFlag" type="boolean" column="active_flag" length="1"/>
<property name="baseMarkupPct" type="big_decimal" column="base_markup_pct" length="9"/>
<property name="closedReasonId" type="string" column="closed_reason_id" length="24"/>
<property name="closedTime" type="timestamp" column="closed_time" length="23"/>
<property name="timeSheetType" type="integer" column="time_sheet_type" length="3"/>
<property name="jobPostingType" type="integer" column="job_posting_type" length="10"/>
<property name="jobTemplateType" type="integer" column="job_template_type" length="10"/>
<property name="hoursPerDay" type="big_decimal" column="hours_per_day" length="9"/>
<property name="billablePerDiem" type="big_decimal" column="billable_per_diem" length="13"/>
<property name="poNumber" type="string" column="po_number" length="30"/>
<property name="trialEndDate" type="timestamp" column="trial_end_date" length="23"/>
<property name="maxSubmission" type="integer" column="max_submission" length="10"/>
<property name="duration" type="integer" column="duration" length="10"/>
<property name="timeSheetFreq" type="integer" column="time_sheet_freq" length="3"/>
<property name="maxExpense" type="big_decimal" column="max_expense" length="13"/>
<property name="approvedTime" type="timestamp" column="approved_time" length="23"/>
<property name="revisionTime" type="timestamp" column="revision_time" length="23"/>
<property name="maxNumberOfBids" type="integer" column="max_number_of_bids" length="3"/>
<property name="bidStartTime" type="timestamp" column="bid_start_time" length="16"/>
<property name="bidEndTime" type="timestamp" column="bid_end_time" length="16"/>
<property name="jobSeekersInBid" type="integer" column="job_seekers_in_bid" length="3"/>
<property name="bidRespondByDate" type="timestamp" column="bid_respond_by_date" length="16"/>
<property name="rateUnit" type="string" column="rate_unit" length="3"/>
<property name="currency" type="string" column="currency" not-null="true" length="3"/>
<property name="serviceType" type="integer" column="service_type" length="3"/>
<property name="hireInvoiceTermsType" type="integer" column="hire_invoice_terms_type" length="3"/>
<property name="hireInvoiceTermsFeePct" type="big_decimal" column="hire_invoice_terms_fee_pct" length="3"/>
<property name="autoInvoiceType" type="integer" column="auto_invoice_type" length="3"/>
<property name="defaultOvertimeBillRateType" type="integer" column="default_overtime_bill_rate_type" length="10"/>

<component name="status" class="insite.business.domain.cwm.JobPostingStatus" insert="true" update="true">
<property name="state" type="integer" column="status" not-null="true" length="3"/>
</component>

<component name="rules" class="insite.business.domain.cwm.JobPostingRules" insert="true" update="true">
<property name="requirePinFlag" type="boolean" column="require_pin_flag" length="1"/>
<property name="tempToPermFlag" type="boolean" column="temp_to_perm_flag" length="1"/>
<property name="requireResumeFlag" type="boolean" column="require_resume_flag" length="1"/>
<property name="allowFinalRateChangeFlag" type="boolean" column="allow_final_rate_change_flag" length="1"/>
<property name="allowRateChangeFlag" type="boolean" column="allow_rate_change_flag" length="1"/>
<property name="workOrderCreationRule" type="integer" column="work_order_creation_rule" length="10"/>
<property name="workOrderExtensionCreationRule" type="integer" column="work_order_extension_creation_rule" length="10"/>
<property name="allowDistributorChangeFlag" type="boolean" column="allow_distributor_change_flag" length="1"/>
<property name="allowCoordinatorChangeFlag" type="boolean" column="allow_coordinator_change_flag" length="1"/>
<property name="autoEngageFlag" type="boolean" column="auto_engage_flag" length="1"/>
<property name="requirePayRateFlag" type="boolean" column="require_pay_rate_flag" length="1"/>
<property name="showPayRateToBuyerFlag" type="boolean" column="show_pay_rate_to_buyer_flag" length="1"/>
<property name="canCopyFlag" type="boolean" column="can_copy_flag" length="1"/>
<property name="showMarkupFlag" type="boolean" column="show_markup_flag" not-null="true" length="1"/>
<!-- <property name="autoInvoicingFlag" type="boolean" column="auto_invoicing_flag" length="1"/>-->
<property name="caTimeSheetRuleFlag" type="boolean" column="ca_time_sheet_rule_flag" length="1"/>
<property name="autoRegisterFlag" type="boolean" column="auto_register_flag" length="1"/>
<!-- <property name="trackTimeExpenseFlag" type="boolean" column="track_time_expense_flag" length="1"/>-->
<!-- <property name="canChangeHireTermsSchedule" type="boolean" column="can_change_hire_terms_schedule" length="1"/>-->
<property name="changeHireTermsScheduleFlag" type="boolean" column="change_hire_terms_schedule_flag" length="1"/>
<property name="visibilityToSupplierRule" type="integer" column="visibility_to_supplier_rule" length="3"/>
<property name="timeInHundredthsOfHoursFlag" type="boolean" column="time_in_hundredths_of_hours_flag" length="1"/>
<property name="titoInMilitaryFormatFlag" type="boolean" column="tito_in_military_format_flag" length="1"/>
<property name="editedByApproverFlag" type="boolean" column="edited_by_approver_flag" length="1"/>
<property name="stopApprovalOnExceedingBudgetFlag" type="boolean" column="stop_approval_on_exceeding_budget_flag" length="1"/>
</component>

<component name="baseRate" class="fieldglass.util.Rate">
<property name="rate" type="big_decimal" column="base_rate" length="9"/>
</component>
<component name="billRate" class="fieldglass.util.Rate">
<property name="rate" type="big_decimal" column="bill_rate" length="9"/>
</component>

<component name="overtimeRate" class="fieldglass.util.Rate">
<property name="rate" type="big_decimal" column="overtime_rate" length="9"/>
</component>

<component name="doubleTimeRate" class="fieldglass.util.Rate">
<property name="rate" type="big_decimal" column="double_time_rate" length="9"/>
</component>

<component name="minBaseRate" class="fieldglass.util.Rate">
<property name="rate" type="big_decimal" column="min_base_rate" length="9"/>
</component>

<component name="minSalary" class="fieldglass.util.Money">
<property name="amount" type="big_decimal" column="min_salary" length="9"/>
</component>

<component name="maxSalary" class="fieldglass.util.Money">
<property name="amount" type="big_decimal" column="max_salary" length="9"/>
</component>

<set name="costCenterSet" lazy="false" table="job_posting_cost_center" cascade="all">
<key column="job_posting_id"/>
<composite-element class="insite.business.domain.cwm.JobPostingCostCenter">
<property name="allocationPct" column="allocation_pct"/>
<property name="costCenterId" column="cost_center_id"/>
</composite-element>
</set>


<set name="qualSet" lazy="false" table="job_posting_qual" cascade="all">
<key column="job_posting_id"/>
<composite-element class="insite.business.domain.cwm.JobPostingQual">
<property name="qualId" type="string" column="qual_id" not-null="true"/>
<property name="scaleId" type="integer" column="scale_id" not-null="true"/>
<property name="mandatoryFlag" type="boolean" column="mandatory_flag" not-null="true"/>
<property name="rating" type="string" column="rating" not-null="true"/>
<property name="qualCategoryId" type="string" column="qual_category_id"/>
<property name="years" type="big_decimal" column="years"/>
<property name="valueFlag" type="boolean" column="value_flag"/>
</composite-element>
</set>


</class>

</hibernate-mapping>

Whoaaa...
You need to break the example down to it's simplest form so that you can demonstrate the problem to us.
By simplest form I mean two classes, say JobPosting and JobPostingQual (with the minimal amount of properties that demonstrates the problem), the hibernate mappings and a simple main method that executes the code demonstrating the problem. Include the hibernate output in debug mode in your post.
(See the section on Isolate the problem at http://www.hibernate.org/160.html)

Currently I'm can't say what is happening. Perhaps a good starting point for you would be the section on Understanding Collection Performance in the hibernate reference manual.

Justin