Question

I am using Visual Studio 2008 to create a windows app. I want to create a login form in a disconnected manner. I am facing a problem that when I am trying to check the DataTable is filled or not it is showing that it is filled always.

Code for login button:

try
        {
            //getting connectionString
            mcc = new myConnectionClass();
            conString = mcc.MyConnection;
            //opening connection con
            con = new SqlConnection(conString);
            string queryString = "select * from LOGIN_TABLE where LOGIN_ID = @LOGIN_ID and LOGIN_PASSWORD = @LOGIN_PASSWORD";
            //dataset ds , SqlDataAdapter sda
            ds = new DataSet();
            sda = new SqlDataAdapter();
            //sqlcommand 
            cmd = new SqlCommand(queryString, con);
            cmd.Parameters.Add(new SqlParameter("LOGIN_ID", txtLogin.Text));
            cmd.Parameters.Add(new SqlParameter("LOGIN_PASSWORD", txtPass.Text));
            sda.SelectCommand = cmd;

            sda.Fill(ds, "LOGIN_TABLE");
            //datatable dt
            dt = ds.Tables["LOGIN_TABLE"];
            //checking is datatable is empty 
            if (dt != null)
            {
                MessageBox.Show("Login Successed");
            }
            else
            {                   
                MessageBox.Show("Login Failed");
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
        finally
        {
            ds.Clear();
            dt.Clear();
        }

Answer 1

Your error lies in the check for

if(dt != null)

it’s allways true if your LOGIN_TABLE exist

you need to check for number of rows.

if(dt.Rows.Count != 0)

Let me say also that, from a security point of view, storing login e password on a database is not a good idea.