how to handle Invalid cast exception error

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I am getting the following error [Unable to cast object of type 'System.DBNull' to type 'System.String'.] at this line doctor.Dr_Remarks = (string)Reader["Dr_Remarks"];.

My datareader is bringing null value from DB . so pls help me how to handle exception at this line in c#.

Posted 29-Aug-13 23:14pm

MurugappanCTS

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[no name] 30-Aug-13 5:24am

Okay so why are you unable to check to see that it is not null?

2 solutions

Solution 1

This one will also try to cast to string. But the as keyword returns null instead of throwing an exception if the conversion is not feasible:

C#

doctor.Dr_Remarks = Reader["Dr_Remarks"] as string;

What you have to consider is:
Do you really want to get a null value back if the databas stored DBNull?
Or do you wish to branch into some error handling here?
Or do you branch anyway because of a null in Dr_Remarks?

Posted 30-Aug-13 0:25am

lukeer

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MurugappanCTS 30-Aug-13 7:37am

I just wanted to get out of error . may be i can show in the grid column the "null" value from database

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Thomas ktg · Accepted Answer · 2013-08-30T00:27:00

Solution 2

Hi Murugappan,

Include this code to handle the null values from the DataReader.

C#

if(!dataReader.IsDBNull(columnIndexNo))
       return dataReader.GetString(columnIndexNo);
   else
       return string.Empty;

Posted 30-Aug-13 0:27am

Thomas ktg

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MurugappanCTS 31-Aug-13 0:59am

Thanks thomas