/// <summary>
        ///     Adds a new receipt line to the database.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void AddButton_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                if (receiptIdInput.Text.Equals("") || productIdInput.Text.Equals("") || quantityInput.Text.Equals(""))
                {
                    MessageBox.Show("Please input all text boxes.");
                    receiptIdInput.Focus();
                    return;
                }
                else if ((!Regex.IsMatch(receiptIdInput.Text, "^[0-9]*$")) || (!Regex.IsMatch(productIdInput.Text, "^[0-9]*$")) || (!Regex.IsMatch(quantityInput.Text, "^[0-9]*$")))
                {
                    MessageBox.Show("Please input only numerical characters into all text boxes.");
                    receiptIdInput.Focus();
                    return;
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show("An error has occurred, please contact your administrator." + "\n\n" + "The error message is: " + "\n\n" + ex.ToString());
            }

            ReceiptLineObject receiptLine;
            ReceiptObject     receipt = businessLogicLayer.CheckReceiptsByID(int.Parse(receiptIdInput.Text));
            ProductObject     product = businessLogicLayer.CheckProductsByID(int.Parse(productIdInput.Text));

            try
            {
                if (!int.Parse(receiptIdInput.Text).Equals(receipt.receipt_id))
                {
                    MessageBox.Show("The Receipt ID provided does not exist.");
                    receiptIdInput.Focus();
                    return;
                }
                else if (!int.Parse(productIdInput.Text).Equals(product.product_id))
                {
                    MessageBox.Show("The Product ID provided does not exist.");
                    productIdInput.Focus();
                    return;
                }
                else
                {
                    receiptLine = businessLogicLayer.InsertNewReceiptLine(int.Parse(receiptIdInput.Text), int.Parse(productIdInput.Text), int.Parse(quantityInput.Text));
                    MessageBox.Show("The provided Receipt Line has been added to the system.");
                    return;
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show("An error has occurred, please contact your administrator." + "\n\n" + "The error message is: " + "\n\n" + ex.ToString());
            }
        }