c#中sqlserver数据库事务处理

private void btn_Click(object sender, System.EventArgs e)
        {
            string conn = ConfigurationSettings.AppSettings["connectstring"];
            SqlConnection cnn = new SqlConnection(conn);
            SqlCommand cmd = new SqlCommand();
            SqlTransaction transaction = null;

            try
            {
                cnn.Open();

                transaction = cnn.BeginTransaction();
                cmd.Transaction = transaction;
                cmd.Connection = cnn;

                string str1 = "";
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = str1;
                cmd.ExecuteNonQuery();

                string str2= "";
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = str2;
                cmd.ExecuteNonQuery();


                transaction.Commit();
            }
            catch(Exception ex)
            {
                transaction.Rollback();
            }
            finally
            {
                cnn.Close();
            }
        }