Help with Object Data Source

I am creating a simple login function using an objectdatasource.
How can I check how many rows are selected after I run the query?
here is my dataobject

Code:

---

[DataObject(true)]
public static class MembershipDB
{
    [DataObjectMethod(DataObjectMethodType.Select)]
        public static IEnumerable CheckMembership(string username, string password)
        {
        SqlConnection con = new SqlConnection(ConnectionString.GetConnectionString());
        string sel = "SELECT * from Membership WHERE Membership.UserName = @ username AND Membership.Password=@password";
        SqlCommand cmd = new SqlCommand(sel, con);
        cmd.Parameters.AddWithValue("userName", username);
        cmd.Parameters.AddWithValue("password", password);
        con.Open();
        SqlDataReader dr = cmd.ExecuteReader(CommandBehavior.CloseConnection);
        return dr;
               
    }
}

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and here is where I call the selectmethod on a btn click

Code:

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protected void BTNLogin_Click(object sender, EventArgs e)
    {
        ObjectDataSource1.Select();

    }

---

I just need to make sure the username and password that is sent is in the database, so how do i see if the rows affected = 0?
Thanks!
oh my object datasource is bound the this dataobject with the parameters with values set to textboxes on the form