Object cannot be cast from dbnull to other types

Question

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double monny = 0;
            try
            {
                if (cn.State.ToString() != "Open")
                    cn.Open();
                cmd = new SqlCommand("select BUY,ADAD from INCREMENT_MADA ", cn);
                dr = cmd.ExecuteReader();
                while (dr.Read())
                {
                    monny += Convert.ToDouble(dr["BUY"]) * Convert.ToDouble(dr["ADAD"]);
                }
                
                dr.Close();
                label9.Text = "";
                label9.Text = monny.ToString();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
            finally
            {
               
                cmd.Cancel();
            }

Posted 14-Jun-16 1:23am

waleed_akre

Updated 14-Jun-16 2:29am

CHill60

v2

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Comments

ZurdoDev 14-Jun-16 7:28am

The error seems pretty clear, doesn't it? You're trying to convert null to double. Can't do that.

waleed_akre 14-Jun-16 7:35am

please check my error and send me thank you....

CHill60 14-Jun-16 7:36am

Send you what? You can't convert null to a double. What are the values on the database? (hint - at least one of them is null)

waleed_akre 14-Jun-16 7:39am

please check my code and send me thank you....

CHill60 14-Jun-16 7:47am

send you what?

waleed_akre 14-Jun-16 7:52am

my code repeat send me

ZurdoDev 14-Jun-16 7:40am

First off, you haven't even told us which line of code is causing the error so we can only guess which line it is. Second, you use Double.TryParse to handle nulls but you should also use COALESCE in your sql statement so that nulls are handled on the server side and never end up in your code.

Tadit Dash (ତଡିତ୍ କୁମାର ଦାଶ) 14-Jun-16 7:40am

Check for null before populating data.

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F-ES Sitecore · Accepted Answer · 2016-06-14T01:43:00

You need to check if the values are database nulls before you use them (a database null is not the same as c# null). Something like

C#

while (dr.Read())
 {
  double buy = dr["BUY"] == DBNull.Value ? 0 : Convert.ToDouble(dr["BUY"]);
  double adad = dr["ADAD"] == DBNull.Value ? 0 : Convert.ToDouble(dr["ADAD"]);

 monny += buy * adad;
 }

This code assume you use 0 for the value when it is null, if you want it to do something else then code in whatever logic you want.

CHill60 · Accepted Answer · 2016-06-14T02:29:00

An alternative to Solution 1 - let the SQL do all the work...

C#

double monny = 0;
using (var cn = new SqlConnection(connectionString))
{
    cn.Open();
    var cmd = new SqlCommand("SELECT SUM(ISNULL(BUY,0) * ISNULL(ADAD,0)) AS res FROM INCREMENT_MADA", cn);
    var dr = cmd.ExecuteReader();
    if (dr.Read())
        monny = Double.Parse(dr["res"].ToString());
    dr.Close();
}
label9.Text = monny.ToString();

Object cannot be cast from dbnull to other types

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