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Cannot set Column 'myCol' to null. Please use DBNull instead

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14 Answers, 1 is accepted

answered on 14 Jul 2010, 03:27 PM

Certainly...

(I hope this looks okay for you - for some reason for me this block is displayed at the top of the web page,)

An exception has occurred while processing '' item:

System.ArgumentException: Cannot set Column 'myColumn' to be null. Please use DBNull instead.

at System.Data.DataRow.set_Item(DataColumn column, Object value)

at System.Data.DataRow.set_Item(String columnName, Object value)

at Telerik.Reporting.Charting.DataHelper.CreateDataHelper(Object dataSource, String dataMember, Boolean isDesign)

at Telerik.Reporting.Charting.DataManager.DataBind()

at Telerik.Reporting.Processing.Chart.ProcessItem()

at Telerik.Reporting.Processing.ReportItemBase.Process(DataMember data)

Accepted

answered on 15 Jul 2010, 05:41 PM

Hi Jason,

This is an issue with the chart's data binding when there is a nullable numeric column in the result. To resolve the problem you can proceed in two ways. First you can create a separate stored procedure only for the chart which does not return such columns especially if not needed. Second, you can fill a DataTable and pass it directly to the chart's data source in the NeedDataSource event of the chart as in the example:

void chart1_NeedDataSource(object sender, System.EventArgs e)

{

var chart = (Telerik.Reporting.Processing.Chart)sender;

var selectCommand = new SqlCommand();

selectCommand.Connection = new SqlConnection("Data Source=.\\SQLEXPRESS;Initial Catalog=AdventureWorks;Integrated Security=True");

selectCommand.CommandType = CommandType.Text;

selectCommand.CommandText = "SELECT TOP 10 * FROM AdventureWorks.Production.Product WHERE Weight IS NULL";

var adapter = new SqlDataAdapter(selectCommand);

var dataTable = new DataTable();

adapter.Fill(dataTable);

chart.DataSource = dataTable;

}

In order the NeedDataSource event to be fired make sure that the Chart item does not have an assigned data source (DataSource property should remain null) until the event is fired.

Hope this helps.

Greetings,
Chavdar
the Telerik team

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answered on 10 Mar 2012, 01:38 AM

Hi Steve (& Joe),

I too am now using Q1 2011 SP1 and am able to confirm that the fix explained on Jul 15, 2010 NO LONGER WORKS. The error that is returned is the "Please use DBNull" error. (The Jul 2010 fix was to fill a DataTable and pass it directly to the chart's data source in the NeedDataSource event of the chart, which worked fine up until SP1.)

For my purposes, I need to differentiate between NULL values & zero values, so just setting a value to zero will not work. (NULL values on my chart indicate that we do not yet have a value available.)

Now, I have found a work around for this problem. Before binding the DataTable to the chart's datasource, pass it through a subroutine that will replace any of the nullable column values with an "empty" value. THE ONLY "empty" value that would work for me is: System.Double.NaN. (Note that I tried several different ways of doing this, but this is the only one that would NOT flip to a zero when the chart was drawn. Instead, this way the point & lines are not drawn at all, which is exactly what I need.)

See the example below:

Private Sub ResetNull(ByVal pTable As DataTable)

'THIS IS A NEW SUB TO FIX A BUG WITH TELERIK REPORTING Q1 2011 SP1 (5.0.11.510)

For Each oRow As DataRow In pTable.Rows

'for each of the nullable columns, reset the value to an empty one

If IsDBNull(oRow.Item("myCol")) Then

oRow.Item("myCol") = System.Double.NaN

End If

Next

End Sub

Hope this helps!

Tina