2

我正在从网站上做一个约会功能。它可以在创建新约会之前比较日期和时间，如果数据库中存在相同日期和时间的用户键，它将弹出消息框。当我尝试插入与 db 不同的日期和时间时，它给了我错误。 错误

我在这一行收到错误：

string dtime = time.ExecuteScalar().ToString();

我不知道我的代码有什么问题，谁能指出我？谢谢。这是我的代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Configuration;
using System.Windows.Forms;
public partial class MakeAppointment : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{

}
protected void Button1_Click(object sender, EventArgs e)
{
    string appointmentdate = Convert.ToString(DropDownListDay.Text + "-" + DropDownListMonth.Text + "-" + DropDownListYear.Text);
    string appointmenttime = Convert.ToString(DropDownListHour.Text + ":" + DropDownListMinute.Text + ":" + DropDownListSecond.Text + " " + DropDownListSession.Text);

    SqlConnection con = new SqlConnection("Data Source=USER-PC;Initial Catalog=webservice_database;Integrated Security=True");
    con.Open();
    SqlCommand date = new SqlCommand("Select adate from customer_registration where adate='"+ appointmentdate +"'",con);
    string ddate = date.ExecuteScalar().ToString();
    con.Close();
    if (ddate == appointmentdate)
    {
        con.Open();
        SqlCommand time = new SqlCommand("Select atime from customer_registration where atime='"+ appointmenttime +"'", con);
        string dtime = time.ExecuteScalar().ToString();
        con.Close();

        if (dtime == appointmenttime)
        {
            MessageBox.Show("This appointment is not available. Please choose other date & time.");
        }
}
}
4

3 回答 3

2

似乎有问题，ExcuteScalar(); 因为它null在查询不存在记录时返回。

你可以这样使用

   var data= date.ExecuteScalar();
   if(data!=null)
         ddate =data.ToString();

细节

ExecuteScalar 抛出 NullReferenceException

于 2013-01-06T12:18:34.873 回答
1

试试这个

using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Configuration;
using System.Windows.Forms;
using System;
public partial class MakeAppointment : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        string appointmentdate = Convert.ToString(DropDownListDay.Text + "-" + DropDownListMonth.Text + "-" + DropDownListYear.Text);
        string appointmenttime = Convert.ToString(DropDownListHour.Text + ":" + DropDownListMinute.Text + ":" + DropDownListSecond.Text + " " + DropDownListSession.Text);

        using (SqlConnection con = new SqlConnection("Data Source=USER-PC;Initial Catalog=webservice_database;Integrated Security=True"))
        {
            con.Open();
            SqlCommand date = new SqlCommand("Select adate from customer_registration where adate='" + appointmentdate + "'", con);
            string ddate = date.ExecuteScalar().ToString();
            if (ddate == appointmentdate)
            {
                SqlCommand time = new SqlCommand("Select atime from customer_registration where atime='" + appointmenttime + "'", con);
                var rtime = time.ExecuteScalar();
                if (rtime != null)
                {
                    string dtime = rtime.ToString();

                    if (dtime == appointmenttime)
                    {
                        MessageBox.Show("This appointment is not available. Please choose other date & time.");
                    }
                }
                else
                {
                    MessageBox.Show("Failed to fetch time from database");
                }
            }
            con.Close();
        }
    }
}
于 2013-01-06T12:10:21.760 回答
0

看起来您的问题是，当您对 ExecuteScalar 的调用未返回任何值时，时间变量为空。在尝试调用它的 ExecuteScalar 成员之前，只需检查时间变量是否有效（！= null）。

于 2013-01-06T12:03:58.210 回答