I have a general question on Parent child mapping, two following objects :
(Nhibernate 1.2)

Parent object mapping
<class name="BaseCustomer, com.xxx.Business" table="CUSTOMER.CUSTOMER">
<id name="Id" column="Customerid" type="Int64" unsaved-value="0">
<generator class="sequence">
<param name="sequence">SEQ_CUSTOMER</param>
</generator>
</id>
<property name="Firstname" column="Firstname" type="String" />
<property name="Lastname" column="Lastname" type="String" />
<bag name="HistoryNotes" cascade="all" inverse="true" >
<key column="Customerid" />
<one-to-many class="Customerhistory, com.xxx.Business" />
</bag>
</class>

Child object mapping
<class name="Customerhistory, com.xxx.Business" table="CUSTOMER.CUSTOMERHISTORY">
<id name="Id" column="Customerhistoryid" type="Int64" unsaved-value="0">
<generator class="sequence">
<param name="sequence">seq_customerhistory</param>
</generator>
</id>
<property name="Description" column="Description" type="String" />
<property name="Systemnote" column="Systemnote" type="Int64" />

<!-- bidirectional mapping to the contact-->
<many-to-one name="ParentBaseCustomer"
class="BaseCustomer, com.xxx.Business"
column="Customerid" not-null="true"/>
</class>


If I'm creating a new parent object and attaching new child objects I'm getting an error when saving . The error is because of the constraint between the child and the parent (in the time I added the child objects the parent didn't had a identifier).
Should I save/flush the parent object before I'm saving the child object ?

When creating a new parent and child in the same session, save the parent before associating the child. You don't need to flush.

AFAIK this is not supposed to be necessary, and is a bug ...

It is working for an existing item , so i might be a bug
If it's a bug , should I submit it any where ?

You can submit bugs to the NHibernate JIRA:
http://www.hibernate.org/217.html