public static readonly string[] FormatOperator

class MyPage : System.Web.UI.Page
{
   public int UpdateStock(Dynamicweb.eCommerce.Orders.Order order, Dynamicweb.eCommerce.Products.Product.OrderStockOperator _Operator)
   {
       Dynamicweb.eCommerce.Products.Product product = new Product();
       string SQL = string.Empty;
       int updateCount = 0;

       foreach (Dynamicweb.eCommerce.Orders.OrderLine orderLine in order.OrderLines)
       {
           if (!(orderLine.Product.Type == ProductType.Service))
           {
               Dynamicweb.eCommerce.Stocks.StockStatus oldStockStatus = orderLine.Product.get_StockStatus(orderLine.Product.LanguageID);

               if (!string.IsNullOrEmpty(orderLine.UnitID))
               {
                   if (UnitExists(orderLine.UnitID))
                   {
                       SQL = "UPDATE EcomStockUnit SET StockUnitQuantity = StockUnitQuantity " + Dynamicweb.eCommerce.Products.Product.FormatOperator[(int)_Operator] + " " + orderLine.Quantity + " ";
                       SQL += "WHERE StockUnitProductID = '" + orderLine.ProductID + "' AND StockUnitID = '" + orderLine.UnitID + "' ";
                       if (!string.IsNullOrEmpty(orderLine.ProductVariantID))
                       {
                           SQL += "AND StockUnitVariantID = '" + orderLine.ProductVariantID + "' ";
                       }
                   }
                   else { continue; }
               }
               else { continue; }

               if (Database.ExecuteNonQuery(SQL, "Ecom.mdb") > 0)
               {
                   updateCount += 1;
               }
           }
       }

       return updateCount;
   }

   public static bool UnitExists(string unitId)
   {
       foreach (Dynamicweb.eCommerce.Variants.VariantOption u in Dynamicweb.eCommerce.Common.Context.Units)
       {
           if (u.ID == unitId)
           {
               return true;
           }
       }

       return false;
   }
}