Doc:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
	<class name="BusinessObjects.BO.Doc,BusinessObjects" table="DOC">
		<id name="Id" column="ID_DOC" type="Decimal" unsaved-value="0">
      <generator class="sequence">
        <param name="sequence">G_ID_DOC</param>
      </generator>
    </id>

    <version column="CHANGE_STAMP" type="Int32" name="ChangeStamp" unsaved-value="0" />
    <!--<version column="ORA_ROWSCN" type="Int64" name="ChangeStamp" generated="always" />-->

    <property column="NAME" type="String" name="Name" not-null="true" length="512" />
		<property column="DESCRIPTION" type="String" name="Description" length="1024" />

    <bag name="DocItems" table="DOC_ITEM" cascade="all" >
      <key column="ID_DOC" />
      <one-to-many class="BusinessObjects.BO.DocItem,BusinessObjects" not-found="ignore" />
    </bag>
   
  </class>
</hibernate-mapping>


DocItem:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
	<class name="BusinessObjects.BO.DocItem,BusinessObjects" table="DOC_ITEM">

		<id name="Id" column="ID_DOC_ITEM" type="Decimal" unsaved-value="0">
      <generator class="sequence">
        <param name="sequence">G_ID_DOC_ITEM</param>
      </generator>
		</id>
		
    <many-to-one name="Doc" column="ID_DOC" class="BusinessObjects.BO.Doc,BusinessObjects" not-null="true" />
    
    <property column="ID_PRODUCT" type="Decimal" name="ProductId" not-null="true" />
    <property column="NUM" type="Decimal" name="Num" not-null="true" />
		<property column="COST" type="Decimal" name="Cost" not-null="true" />

  </class>
</hibernate-mapping>

                using (var tx = _session.BeginTransaction())
                {
                    _session.Delete(doc);

                    tx.Commit();
                }

                using (var tx = _session.BeginTransaction())
                {
                    _session.Update(obj);

                    tx.Commit();
                }