List <IEnumerable <SalesSummaryItem> > GetSalesSummaryItems()
 {
     return(new List <IEnumerable <SalesSummaryItem> >()
     {
         QueriesHelper.GetSalesSummaryItems(unitOfWork.OrderItems, Period.ThisYear),
         QueriesHelper.GetSalesSummaryItems(unitOfWork.OrderItems, Period.ThisMonth),
         QueriesHelper.GetSalesSummaryItems(unitOfWork.OrderItems, Period.FixedDate, LastOrderDate(unitOfWork))
     });
 }