DataReader不从MySqlDatabase获取值

Question

我有一个datagridview，其中包含bio_id和电子邮件。我正在迭代datagridview以根据bio_id和日期获取员工的时间记录。如果我在MySql本身中创建一个MySql语法，它会获得正确的值，但是当我使用MySqlDataReader时，它会给我一个空值。以下是代码：

public MySqlDataReader SendTimeLogs(string fromDate, string toDate, int bioId)
        {
            using (var cn = new DatabaseConnection().ConnectToMySql())
            {
                const string query = @"SELECT MIN(scan_time) as 'Time In', MAX(scan_time) as 'Time Out', 
                TIMEDIFF(MAX(scan_time),MIN(scan_time)) as difference 
                FROM `filtered_dates` 
                WHERE bio_id = @bioId AND date BETWEEN @fromDate AND @toDate GROUP BY date ORDER BY date asc";
                var cmd = new MySqlCommand(query, cn);
                cn.Open();
                cmd.Parameters.AddWithValue("@fromDate", fromDate);
                cmd.Parameters.AddWithValue("@toDate", toDate);
                cmd.Parameters.AddWithValue("@bioId", bioId);
                return cmd.ExecuteReader();       
            }
        }

private void SendEmail()
        {

            var rdr = new EmployeeDataAccess().GetBioIdEmail();
            while (rdr.HasRows && rdr.Read())
            {
                dgvBioIdList.Rows.Add(rdr["bio_id"].ToString(), rdr["email_add"].ToString());
            }


            for (var i = 0; i < dgvBioIdList.Rows.Count; i++)
            {
                var message = "Time Logs for Bio ID: " +dgvBioIdList.Rows[i].Cells[0].Value;
                var x = new FilteredDatesDataAccess();
                var timeLogs = x.SendTimeLogs(dtpStart.Text, dtpStop.Text,
                    Convert.ToInt32(dgvBioIdList.Rows[i].Cells[0].Value));
                var rec = dgvBioIdList.Rows[0].Cells[1].Value.ToString();

                Console.WriteLine(message);
                Console.WriteLine(rec);
                while (timeLogs.HasRows && timeLogs.Read())
                {
                    Console.WriteLine(timeLogs["Time In"] + @" - " + timeLogs["Time Out"]);
                }
            }
        }

我得到Console.WriteLine（消息）;和Console.WriteLine（rec）;很好但我的while循环没有写在控制台中。你能帮我吗？谢谢。