public void LoadData()
        {
            Customer.PurchaseHistory.Clear();

            foreach (Purchase purchase in PurchaseManager.GetAllById(Customer.Info.Id, "CustomerId"))
            {
                Customer.PurchaseHistory.Add(new PurchaseHistory(purchase));
            }

            foreach (PurchaseHistory purchaseHistory in Customer.PurchaseHistory)
            {
                foreach (PurchaseItem purchaseItem in PurchaseItemManager.GetAllById(purchaseHistory.Purchase.Id, "PurchaseId"))
                {
                    purchaseHistory.PurchaseDetails.Add(new PurchaseDetails(purchaseItem, ItemManager.GetById(purchaseItem.ItemId, "Id")));
                }
            }
        }