Error - No mapping exists from object type System.Web.UI.WebControls.HiddenField to a known managed provider native type.

Question

User-1499457942 posted

Hi

  I have below code . On below line it is giving above error

String ret = Convert.ToString(cmd.ExecuteScalar());

protected void ListView_ItemDataBound(object sender, ListViewItemEventArgs e)
        {
            try
            {
                Label lblCustomerNo = (Label)e.Item.FindControl("lblCustomerNo");
                Label lblCustomerName = (Label)e.Item.FindControl("lblCustomerName");
                HiddenField hdfENo = (HiddenField)e.Item.FindControl("hdfENo");

                SqlCommand cmd;
                cmd = new SqlCommand("select Left([Status],1) from [tbl_G] where [ENo]=@ENo", con);
                cmd.CommandType = CommandType.Text;
                cmd.Parameters.AddWithValue("@ENo", hdfENo);
                String ret = Convert.ToString(cmd.ExecuteScalar());
                cmd.Dispose();
            }
            catch (Exception ex)
            {
            }
        }

Thanks

Answer 1

User475983607 posted

Execute Scalar returns an object.  The convention and recommendations in your other post have this syntax.  There's also reading the openly published documentation.

https://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlcommand.executescalar(v=vs.110).aspx

string ret = (string)cmd.ExecuteScalar();

Lastly, are you sure Convert.ToString() is causing the error?  You're hiding exceptions with an empty catch block.  Please take a moment to run your code through the Visual Studio debugger. 

Answer 2

User409696431 posted

I believe the problem is with this line:

cmd.Parameters.AddWithValue("@ENo", hdfENo);

hdfEo is a HiddenField control, not a value.   You should pass the value of the HiddenField, not the HIddenField control itself.

cmd.Parameters.AddWithValue("@ENo", hdfENo.Value);

(This assumes you know you'll have a valid value in that HiddenField, otherwise you should validate that first.)