I have been looking for a way to evaluate if a column in a database has a null value in it. So far, every method suggested have failed and I would like to know anyone else have successfully evaluate a null value in C# Visual Studio 2005.

you can use nullable types i.e. - int? myVar = ... ;

you can also check to see if the value is = to System.DbNull...

How exactly do I do that, I've use IsDBNull, Convert.IsDBNull, IsDBNull.Value and nothing works and I've tried type casting. ????

The following can help you but i am sure whether this is the right way.

While selecting the column check for null values like

select ISNULL(class,-1) from student

If the column class contains null values,the query returns -1 value.
Using this value you can identity the column contains null value.

Good Luck.

You need to compare the column value with System.DBNull.Value

So assuming a DataTable for example:

if( myDataTable.Rows[0]["someColumn"].Equals(System.DBNull.Value) )
          //Handle situation for null value.

I tried that method already and it does not work.

Hmm... well it works for me. You'll have to post some code or give more information.

you can also get the value of the cell and use .text.tostring
then test the length of the string len(abc) > 0

Here is the code

    public int TestDBNullValue(string PID)
        int ErrorValue = 0;
        if (PID.Equals(String.Empty))
            ErrorValue = 10110; //PID is null or empty
            DeviceTableAdapter DeviceAdapter = new DeviceTableAdapter();
            JeanPierre.DeviceDataTable DeviceTable = DeviceAdapter.GetDeviceUIDByPID(PID);

            if (DeviceTable.Count.Equals(0))
                ErrorValue = 1111; //No device found
                JeanPierre.DeviceRow DevRows = DeviceTable[0];

                    ErrorValue = 1;
                    ErrorValue = 41;
        return (ErrorValue);

i converted from vb.net to c#, so it might not be accurate...

if (Strings.len(PID) == 0) {

That part of the code works fine. What I was doing there is evaluating whether the query return a row and if it did, I'll move on to the next step and evaluate if the data in the column is NULL (The part I can't get to work).

with the above code it is always guarantee to have a row returned so I don't need to count it. the problem is whether a column is null or not.

so test the length of the text in a cell.

Aha, you are using a strongly typed DataTable.

You must be handling the DBNull somehow otherwise you would be getting an exception when populating the table.

Have you tried just == null ?

Already have and its still the same. Somebody suggested that I use the is null in the query itself but I've never constructed a query like that before. Can anyone of you let me know if it is possible to do that?

There is a good article here on coding for evaluating a null assignment to a database field.

My working solution solution based upon the reading from the page below is as follows

strTemp = rs.Fields(1)
strTemp = "" & strTemp ' to resolved database null evaluation in an IF statement
If strTemp = "" then
returned_rs.stremailaddres = "some string"
returned_rs.stremailaddress = rs.Fields(1)

read for more details

Why don't you try to check null in SQL query ?

SELECT ISNULL(EmployeeAddress,'') as EmployeeAddress FROM MasterEmployee ORDER BY EmployeeID

in code :

If Rd.Item("EmployeeAddress").toString.Trim() ="" Then

End Id