using (SqlConnection testConnection = new SqlConnection(connString))
            { 
                SqlCommand testCommand = 
                    new SqlCommand("Select * from DEMO", testConnection);
                testConnection.Open();
                SqlDataReader sqlDr = 
                    testCommand.ExecuteReader(CommandBehavior.CloseConnection);
                if (sqlDr.HasRows)
                {
                    foreach (DbDataRecord rec in sqlDr)
                    {
                        dbRecordsHolder.Add(rec);  // dbRecordsHolder имеет тип ArrayList
                    }
                }
            }

        private void button1_Click(object sender, EventArgs e)
        {
            myDataGrid.DataSource = dbRecordsHolder;
        }