string AssamblyName = System.Configuration.ConfigurationManager.AppSettings["DefaultEntities"].ToString();
        Configuration cfg = new Configuration();
        cfg.AddAssembly(AssamblyName);
       
       
        ISessionFactory factory = cfg.BuildSessionFactory();
        ISession session = factory.OpenSession();
        ITransaction transaction = session.BeginTransaction();

        Supplier s = new Supplier();
        s.Name = "foo";
        s.CreateDate = DateTime.Now;
        s.LastUpdatedDate = s.CreateDate;

        s.Brands = new List<Brand>();
        Brand b = new Brand("bar");
        s.Brands.Add(b);
        session.Save(s);

        transaction.Commit();

        session.Close();
        session.Dispose();

        Response.Write("oki");

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
   <class name="Swh.Entities.Supplier, Swh.Entities" table="Suppliers">
      <id name="Id" column="SupplierId" type="int" unsaved-value="0">
         <generator class="identity" />
      </id>
      <property name="Name" column="SupplierName" type="String"/>
      <property name="CreateDate" column="CreateDate" type="DateTime"/>
      <property name="LastUpdatedDate" column="LastUpdatedDate" type="DateTime"/>
      <bag name="Brands" lazy="true" cascade="all-delete-orphan" inverse="true">
         <key>
            <column name="SupplierId" not-null="true"/>
         </key>
         <one-to-many class="Swh.Entities.Brand, Swh.Entities"/>
      </bag>
   </class>
</hibernate-mapping>


<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
   <class name="Swh.Entities.Brand, Swh.Entities" table="Brands">
      <id name="Id" column="BrandId" type="int" unsaved-value="0">
         <generator class="identity" />
      </id>
      <many-to-one name="Supplier" class="Swh.Entities.Supplier, Swh.Entities" column="SupplierId" />
      <property name="Name" column="BrandName" type="String"/>
   </class>
</hibernate-mapping>