Programming Forums > Application Development > C#

jonyzz · Apr 11th, 2007, 6:40 AM

Hey guys,
I have a question about selecting data from a MS Sql server database by using a SqlDataReader. The problem is that some of the columns in my table can be null. I want to retrieve a bool value or a null depending on what is in the column. I tried using the bool? type like this:

(Toggle Plain Text)

bool? b = (bool?)reader["ConfirmColumn"];

it compiles, but throws an Invalid Cast exception at runtime if the value in the "ConfirmColumn" is NULL.
Has any of you had the same problem to solve? Any ideas?
Thanks in advance.

pegasus001 · Apr 11th, 2007, 7:22 AM

What is spam? And what is edit?

melbolt · Apr 12th, 2007, 10:13 AM

Hi,

I believe this is what you need

 csharp Syntax (Toggle Plain Text) 
 if (!(reader["ConfirmColumn"] is System.DBNull.Value))
             {
                bool? b = (bool?)reader["ConfirmColumn"];
             }
 if (!(reader["ConfirmColumn"] is System.DBNull.Value))
             {
                bool? b = (bool?)reader["ConfirmColumn"];
             }

I am better with VB .NET so i tried converting it over to C#, one thing to watch out for, I wasn't sure whether or not to use "is" or "==", in VB .NET you use "is" when working with potential null conditionals, wasn't sure if C# was the same or not. so you may need to change it if it doesn't work. try this first though.

good luck

jonyzz · Apr 17th, 2007, 8:15 AM

thank you melbolt - it is a good idea

Apr 11th, 2007, 6:40 AM	#1
jonyzz Programmer Join Date: Aug 2005 Location: null Posts: 40 Rep Power: 0	How to retrieve nullable data from a MS SQL server database by using a DataReader Hey guys, I have a question about selecting data from a MS Sql server database by using a SqlDataReader. The problem is that some of the columns in my table can be null. I want to retrieve a bool value or a null depending on what is in the column. I tried using the bool? type like this: (Toggle Plain Text) bool? b = (bool?)reader["ConfirmColumn"]; bool? b = (bool?)reader["ConfirmColumn"]; it compiles, but throws an Invalid Cast exception at runtime if the value in the "ConfirmColumn" is NULL. Has any of you had the same problem to solve? Any ideas? Thanks in advance.

Apr 11th, 2007, 7:22 AM	#2
pegasus001 Hobbyist Programmer Join Date: Nov 2006 Location: 163H Posts: 213 Rep Power: 2	What is spam? And what is edit? __________________ You never test the depth of a river with both feet. The believer is happy. The doubter is wise. Free speech carries with it some freedom to listen. The next generation will always surpass the previous one. It`s one of the never ending cycles of life.

Apr 12th, 2007, 10:13 AM	#3
melbolt Hobbyist Programmer Join Date: Feb 2005 Location: PA, USA Posts: 237 Rep Power: 4	Hi, I believe this is what you need csharp Syntax (Toggle Plain Text) if (!(reader["ConfirmColumn"] is System.DBNull.Value)) { bool? b = (bool?)reader["ConfirmColumn"]; } if (!(reader["ConfirmColumn"] is System.DBNull.Value)) { bool? b = (bool?)reader["ConfirmColumn"]; } I am better with VB .NET so i tried converting it over to C#, one thing to watch out for, I wasn't sure whether or not to use "is" or "==", in VB .NET you use "is" when working with potential null conditionals, wasn't sure if C# was the same or not. so you may need to change it if it doesn't work. try this first though. good luck __________________ I have never let my schooling interfere with my education. -Mark Twain- Xbox live gamertag: melbolt

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Apr 17th, 2007, 8:15 AM	#4
jonyzz Programmer Join Date: Aug 2005 Location: null Posts: 40 Rep Power: 0	thank you melbolt - it is a good idea

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Programming Forums > Application Development > C#

How to retrieve nullable data from a MS SQL server database by using a DataReader