<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" schema="dbo" assembly="IWaiter.Model"  namespace="IWaiter.Model">
   <class name="CustomerOrder" table="CustomerOrder">
      <id name="Id" column="Id" type="Int32" unsaved-value="0">
         <generator class="identity"/>
      </id>
      <property name="DateCreated" column="DateCreated" type="DateTime" not-null="true" />
      <many-to-one name="CustomerTable" column="CustomerTableId" not-null="true" />
      <list name="LineItems" table="LineItem" lazy="true"  >
         <key column="OrderId"/>
         <index column="LineNumber"/>
         <composite-element class="LineItem" >
            <property name="Quantity" column="Quantity" type="Int32" not-null="true"/>
            <many-to-one name="Product" column="ProductId" not-null="true"/>
         </composite-element>
      </list>
   </class>
</hibernate-mapping>

CustomerOrder order = new CustomerOrder ( );
         order.DateCreated = DateTime.Now;
         order.CustomerTable = new CustomerTableDao ( ).GetById ( 1, false );

         LineItem lineItem = new LineItem ( );
         lineItem.Product = new ProductDao ( ).GetById ( 6, false );
         lineItem.Quantity = 3;
         order.LineItems = new List<LineItem> ( );
         order.LineItems.Add ( lineItem );

         new CustomerOrderDao ( new CustomerTableDao ( ) ).Save ( order );
         new CustomerOrderDao ( new CustomerTableDao ( ) ).NHSession.Clear ( );
         order = new CustomerOrderDao ( new CustomerTableDao ( ) ).GetById ( order.Id, false );

Assert.IsTrue ( order.LineItems.Count > 0 );

<list name="LineItems" table="LineItem" lazy="true" cascade="all" >

new CustomerOrderDao ( new CustomerTableDao ( ) ).Save ( order );
new CustomerOrderDao ( new CustomerTableDao ( ) ).NHSession.Flush ( );
new CustomerOrderDao ( new CustomerTableDao ( ) ).NHSession.Clear ( );