InvalidOperationException when i try to retrieve a password from database, “Invalid attempt to read when no data is present.”

Question

This is my code, I need to retrieve LoginPassword from the database

public partial class frmPassword : Form
{
    SqlConnection connection = new SqlConnection(@"Data Source=WORKSTATION\SQLEXPRESS;Initial Catalog=TPSystem;Integrated Security=True");

    public frmPassword()
    {
        InitializeComponent();
    }

    private void btnUpdatePassword_Click(object sender, EventArgs e)
    {
        frmLogin login = new frmLogin();
        string UserN = login.UName;
        string Pass;
        SqlCommand cmd = new SqlCommand("SELECT Login_Password FROM AdminLogin WHERE Login_Username = '"+UserN+"'", connection);

        try
        {
            connection.Open();
            SqlDataReader reader = cmd.ExecuteReader();
            reader.Read();

            Pass = reader["Login_Password"].ToString();

            if (tbOldPassword.Text == Pass)
                MessageBox.Show("Password matches");
            else
                MessageBox.Show("Password wrong");
            reader.Close();
        }
        catch (SqlException ex)
        {
            MessageBox.Show(ex.Message, "Report", MessageBoxButtons.AbortRetryIgnore, MessageBoxIcon.Error);
        }
        finally
        {
            connection.Close();
        }
    }
}

I got this error on execution:

An unhandled exception of type 'System.InvalidOperationException' occurred in System.Data.dll

Additional information: Invalid attempt to read when no data is present.

Answer 1

The reader.Read() methods returns a boolean to indicate if anything was in fact read - you're not checking that at all....

Change your code to:

if(reader.Read())
{
    Pass = reader["Login_Password"].ToString();

    if (tbOldPassword.Text == Pass)
            MessageBox.Show("Password matches");
    else
            MessageBox.Show("Password wrong");
}

If nothing was read, I guess your user doesn't exist - I'm not sure what you want to do in that case.... up to you

But please tell me you're NOT storing passwords in clear text in your database!!!!

Answer 2

It seems that there is no entry in the database for the username you are checking. Please check if thereader returns a result:

public partial class frmPassword : Form
{
    SqlConnection connection = new SqlConnection(@"Data Source=WORKSTATION\SQLEXPRESS;Initial Catalog=TPSystem;Integrated Security=True");

    public frmPassword()
    {
        InitializeComponent();
    }

    private void btnUpdatePassword_Click(object sender, EventArgs e)
    {
        frmLogin login = new frmLogin();
        string UserN = login.UName;
        string Pass;
        SqlCommand cmd = new SqlCommand("SELECT Login_Password FROM AdminLogin WHERE Login_Username = '"+UserN+"'", connection);

        try
        {
            connection.Open();
            SqlDataReader reader = cmd.ExecuteReader();
            while(reader.Read())
            {
            Pass = reader["Login_Password"].ToString();

            if (tbOldPassword.Text == Pass)
                MessageBox.Show("Password matches");
            else
                MessageBox.Show("Password wrong");
            }
            reader.Close();
        }
        catch (SqlException ex)
        {
            MessageBox.Show(ex.Message, "Report", MessageBoxButtons.AbortRetryIgnore, MessageBoxIcon.Error);
        }
        finally
        {
            connection.Close();
        }
    }
}