SqlDataSource and stored procedure call issue - asp.net

Question

I've stumbled upon an issue and can't figure it out on my own. Hope someone could help me resolve it.
So, I have a simple stored procedure in a SQL Server 2005 database
CREATE PROCEDURE spTest
#pin varchar(128)
AS
BEGIN
SELECT #Pin as Param
END
and an asp.net page with a SqlDataSource and a GridView control in an application (VS2008)
<asp:SqlDataSource
ID="sds2"
runat="server"
ConnectionString="..."
SelectCommand="spTest"
SelectCommandType="StoredProcedure"
>
<SelectParameters>
<asp:QueryStringParameter Name="pin" QueryStringField="pin" DbType="String"/>
</SelectParameters>
</asp:SqlDataSource>
<asp:GridView ID="gv" runat="server" DataSourceID="sds2"></asp:GridView>
As you can see, the code is straightforward. Nevertheless, if I don't bother specify the pin on the url (.../Default.aspx instead of .../Default.aspx?pin=somevalue) or specify an empty line (.../Default.aspx?pin=) there is no any call to the stored procedure (I check it with SQL Server Profiler).
Moreover, if I replace the QueryStringParameter with a simple
<asp:Parameter Name="pin" DbType="String" />
and do not point out DefaultValue value, the situation repeats and no calls to the stored procedure are made. What is the reason of such a behaviour?
I'm quite a new to the asp.net and possibly overlook something, but I even tried to do the same in code-behind file programmatically instead of declaratively and the result is the same. The only thing I could find out is that in such case a Selecting event of the SqlDataSource is fired, but the Selected is not. Maybe some kind of an error happens?
Anyway, any kind of help would be greatly appreciated.

Answer 1

The SqlDataSource object has a property called CancelSelectOnNullParameter. Its default value is true, so I think the behavior you're seeing is expected, albeit not obvious. Try setting this property to false.
<asp:SqlDataSource
ID="sds2"
runat="server"
ConnectionString="..."
SelectCommand="spTest"
SelectCommandType="StoredProcedure"
CancelSelectOnNullParameter="false"
>
Additionally, you may find the ConvertEmptyStringToNull property of the Parameter class (QueryStringParameter extends this) to be of some use, depending on if/how your stored proc handles null values. Its default value is true as well.

Answer 2

Try this out.
Create a method which will return db null if parameter is not passed in the stored procedure
public static object GetDataValue(object o)
{
if (o == null || String.Empty.Equals(o))
return DBNull.Value;
else
return o;
}
Create a method which will called the stored procedure and fill the dataset.
public DataSet GetspTest(string pin)
{
try
{
DataSet oDS = new DataSet();
SqlParameter[] oParam = new SqlParameter[1];
oParam[0] = new SqlParameter("#Pin", GetDataValue(pin));
oDS = SqlHelper.ExecuteDataset(DataConnectionString, CommandType.StoredProcedure, "spTest", oParam);
return oDS;
}
catch (Exception e)
{
ErrorMessage = e.Message;
return null;
}
}
Now bind the dataset to gridview
private void GvTest()
{
DataSet oDsGvspTest = new DataSet();
string pin = Request.QueryString["Pin"];
oDsGvspTest = GetspTest(pin);
if (oDsGvspTest.Tables[0].Rows.Count > 0)
{
Gv.DataSource = oDsGvspTest;
Gv.DataBind();
}
}
Now called this method on page_load event
if(!IsPostBack)
{
GvTest();
}
If found it useful,please mark it as your answer else let me know...