Question

I want to get single value from select query called tenant. Tenant_Facing from SQL Server have single char value that either ‘Y’ or ‘N’. When I execute it, there a error that say “Specified cast is not valid” on Char tenant = (Char)cmd.ExecuteScalar();.
I don’t understand why it not match even they are both Char? Here my codes,

protected void DropDownArchitecture_SelectedIndexChanged(object sender, EventArgs e)
    {

        SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["Database_Shared_NotebookConnectionString"].ConnectionString);

        string architecture = ((DropDownList)GridViewServer.FooterRow.FindControl("DropDownArchitecture")).Text;

        SqlCommand cmd = new SqlCommand("SELECT Tenant_Facing FROM tblArchitecture WHERE Architecture = '" + architecture + "'");

        cmd.Connection = conn;

        conn.Open();

        Char tenant = (Char)cmd.ExecuteScalar();

        conn.Close();

        if (tenant == 'Y')
        {
            ((DropDownList)GridViewServer.FooterRow.FindControl("DropDownTenant")).Visible = true;
        }
        else
        {
            ((DropDownList)GridViewServer.FooterRow.FindControl("DropDownTenant")).Visible = false;
        }
    }

Answer 1

Even though your data type in SQL Server is a single char, that type still maps to string in ADO.NET. Try it like this instead:

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

conn.Close();

if (tenant == "Y")
//            ^ ^ make sure to change these to double-quotes
{
    ((DropDownList)GridViewServer.FooterRow.FindControl("DropDownTenant")).Visible = true;
}
else
{
    ((DropDownList)GridViewServer.FooterRow.FindControl("DropDownTenant")).Visible = false;
}