Solved

Handling null values in Command.ExecuteScalar using C#

Posted on 2015-02-21
9
141 Views
Last Modified: 2015-02-23
I am trying to get some values from the database but when no values are returned i get this error" "Specified cast is not valid"  but the code works fine when data comes back from the database specially when Checked = 1 is true.  How can i overcome  with null values  in Command.ExecuteScalar?
     using (SqlConnection con = new SqlConnection(strConnString))
            {
                using (SqlCommand cmd = new SqlCommand())
                {
                    cmd.Connection = con;
                    cmd.CommandType = CommandType.Text;
                    cmd.CommandText = @"select DATEDIFF(minute, Min(FullDatetime), Max(FullDatetime)) / 60.0 as hours                 
                      from   myTable
                       where userid = @UserID
                        and DT_Submitted = (select CAST(FLOOR( CAST( GETDATE() AS FLOAT ) )AS DATETIME))
                         and Checked = 1";

                    cmd.Parameters.AddWithValue("@UserID", tempUser.ToString());
                    con.Open();
                    decimal result = (decimal)cmd.ExecuteScalar();
                    lblHours.Text = result.ToString("0.#") + " Hours";

                    con.Close();
                    con.Dispose();
                }
            }

Open in new window

it is failing at this line
decimal result = (decimal)cmd.ExecuteScalar();

Open in new window

0
Comment
Question by:moe57
  • 5
  • 3
9 Comments
 
LVL 63

Expert Comment

by:Fernando Soto
ID: 40623302
Hi moe57;

You can change your code like this.

decimal? resultNullable = (decimal?)cmd.ExecuteScalar();
decimal result = 0.0m;

if ( resultNullable.HasValue )
{
    result = resultNullable.Value;    
}

Open in new window

0
 
LVL 44

Expert Comment

by:AndyAinscow
ID: 40623322
Just to explain a little the decimal? means that the variable is a decimal OR a null.
0
 

Author Comment

by:moe57
ID: 40623860
sometimes it is null but also sometimes we get some decimal values too
0
Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 
LVL 63

Accepted Solution

by:
Fernando Soto earned 500 total points
ID: 40624215
Yes, and because there is a possibility that the return value can be a null you need to guard against it so that the end user does not have the program crash on them. There for my solution which does that.

Repost of my previous solution

decimal? resultNullable = (decimal?)cmd.ExecuteScalar();
decimal result = 0.0m;

if ( resultNullable.HasValue )
{
    result = resultNullable.Value;    
}

Open in new window

0
 

Author Comment

by:moe57
ID: 40625545
i am still getting this error:  Specified cast is not valid.
0
 
LVL 63

Expert Comment

by:Fernando Soto
ID: 40625603
On what line are you getting the exception?
What is the full exception message and inner exception message.
Please post the code as you implemented it in the program.
What is the database data type being returned from the database?
0
 

Author Comment

by:moe57
ID: 40625608
i have resolved my problem
 if (cmd.ExecuteScalar() == DBNull.Value)
                    {
                        lblHours.Text = "you have not selected any hours";
                    }else
                    {
                        decimal result = (decimal)cmd.ExecuteScalar();
                        lblHours.Text = result.ToString("0.#") + " Hours";
                    }

Open in new window

0
 

Author Comment

by:moe57
ID: 40625609
thanks you have helped me in the right direction.
0
 

Author Closing Comment

by:moe57
ID: 40625673
thx
0

Featured Post

Forrester Webinar: xMatters Delivers 261% ROI

Guest speaker Dean Davison, Forrester Principal Consultant, explains how a Fortune 500 communication company using xMatters found these results: Achieved a 261% ROI, Experienced $753,280 in net present value benefits over 3 years and Reduced MTTR by 91% for tier 1 incidents.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
API v SOA 8 39
orderby list (from Json) 1 29
Images showing on the internet -- asp.net -- VB.net.  Why some do and some don’t. 3 24
Adjust the codes 3 29
Problem Hi all,    While many today have fast Internet connection, there are many still who do not, or are connecting through devices with a slower connect, so light web pages and fast load times are still popular.    If your ASP.NET page …
It was really hard time for me to get the understanding of Delegates in C#. I went through many websites and articles but I found them very clumsy. After going through those sites, I noted down the points in a easy way so here I am sharing that unde…
The Email Laundry PDF encryption service allows companies to send confidential encrypted  emails to anybody. The PDF document can also contain attachments that are embedded in the encrypted PDF. The password is randomly generated by The Email Laundr…
Are you ready to implement Active Directory best practices without reading 300+ pages? You're in luck. In this webinar hosted by Skyport Systems, you gain insight into Microsoft's latest comprehensive guide, with tips on the best and easiest way…

749 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question