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Web アプリケーションのバグをつぶそうとしています。基本的にレストラン予約システムを実装しようとしています。ユーザーは、パーティーの人数、着席 (ランチまたはディナー)、および日付を選択します。次に、システムはデータベースにクエリを実行して、空きがあるかどうかをユーザーに知らせます。レストランにすでに予約済みの人がいる場合は機能しますが、クエリが NULL 値を返す場合 (つまり、レストランが空である場合)、システムがクラッシュします。このように NULL を処理する必要はありませんでした。ユーザーが予約できるように、コードでこのエラーを処理する方法に途方に暮れています。できる限り自分のコードにコメントしました。どんな助けでも大歓迎です！:)

protected void AvailabilityButton_Click(object sender, EventArgs e)
{
    //Create SQL Database connection
    // New sql connection and command
    SqlConnection myconn = new SqlConnection();
    myconn.ConnectionString = "Data Source=STUDENT2;Initial Catalog=HarryBistro;Integrated Security=True";
    SqlCommand cmd = new SqlCommand();
    cmd.Connection = myconn;
    myconn.Open();

    //Check that selected date is today or later
    if (Calendar1.SelectedDate <= DateTime.Today)
    {
        SuccessFailureLabel.Text = "Please select a date in the future";
        SuccessFailureLabel.Visible = true;
    }
    else
    {
        //Create variables from user input
        string SelectedBranch = BranchDropDownList.SelectedValue.ToString();
        string SelectedSitting = SittingDropDownList.SelectedValue.ToString();
        int SelectedDiners = Convert.ToInt32(DinersDropDownList.SelectedValue);
        string SelectedDate = Calendar1.SelectedDate.ToString("yyyy-MM-dd");


        //Query to find out how many people have already booked into selected restaurant on selected date on selected sitting 
        cmd.CommandText = "select SUM(Number_Of_Seats) from RESERVATIONS where Sitting = '" + SelectedSitting + "' and Branch_ID = '" + SelectedBranch + "' and Date_Of_Booking = '" + SelectedDate + "' ";

        //Assign the value of the people in the restaurant to a variable
        int peopleinrestaurant = (int)cmd.ExecuteScalar();

        //Query to find out how many people the selected restaurant seats 
        cmd.CommandText = "select SUM(Capacity) from BRANCH where Branch_ID = '" + SelectedBranch + "'";

        //Assign the value of the people in the restaurant to a variable
        int branchCapacity = (int)cmd.ExecuteScalar();

        //add the amount of people in the party to the restaurant occupancy and assign to a variable
        int totalOccupancy = peopleinrestaurant + SelectedDiners;

        if (totalOccupancy <= branchCapacity)
        {
            //Show success message
            SuccessFailureLabel.Visible = true;
            SuccessFailureLabel.Text = "Booking available. Please proceed.";

            //enable customer details text boxes so the customer can proceed                 
            ConfirmBookingButton.Enabled = true;
        }

        else
        {
            //Show failure message if booking over capacity. Show user how many seats are available
            SuccessFailureLabel.Visible = true;
            SuccessFailureLabel.Text = "Cannot proceed. There are only " + (branchCapacity - peopleinrestaurant) + " seats available.";
        }
    }
}
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5 に答える 5

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を使用して、戻り値が null かどうかを確認できます

isnull(your query,replacement_value)
于 2013-11-12T10:19:47.377 に答える