从数据库计算时间

Question

I am trying to make my program calculate a break time with data stored in an mysql database.

private void timerpause_Tick(object sender, EventArgs e)
        {
            MySqlConnection conn = DBUtils.GetDBConnection();
            conn.Open();

            MySqlCommand dbrequest = conn.CreateCommand();
            dbrequest.CommandText = "SELECT pstart FROM arbeitszeiten WHERE fullname = '" + textBoxfullname.Text + "' and active = 'JA'";
            string pausebeginn = dbrequest.ExecuteScalar().ToString();

            MySqlCommand dbrequest2 = conn.CreateCommand();
            dbrequest2.CommandText = "SELECT ptotal FROM arbeitszeiten WHERE fullname = '" + textBoxfullname.Text + "' and active = 'JA'";
            string pausenzeit = dbrequest2.ExecuteScalar().ToString();

            TimeSpan pause = Convert.ToDateTime(pausenzeit).TimeOfDay;
            DateTime start = Convert.ToDateTime(pausebeginn);
            TimeSpan zwischen = (DateTime.Now - Convert.ToDateTime(start)).Add(pause);


            label1.Text = zwischen.ToString();

            conn.Close();
        }

When the code is executed it tells me:

TimeSpan pause = Convert.ToDateTime(pausenzeit).TimeOfDay;

The charters are not detected as a valid DateTime value (Die Zeichenfolge wurde nicht als gültiges DateTime erkannt)

Format:

 DB pstart = yyyy-MM-dd HH:mm:ss
 DB ptotal = HH:mm:ss

Does anyone see my mistake (besides not having the requests parameterized yet)?

Answer 1

I agree with everyone else here that the best case scenario is that your dates should be stored as dates.I am going to make some assumptions. One that your database is out of your control or too time consuming/ not a priority to deal with for what ever reason. So i will assume that makes your question how vest to parse your dates and time spans in those formats. Im also going to assume you deal with nulls and format exceptions for dodgy data separately.

Personally i prefer to use the parse exact method on both the date time. You can use it like so usng your formats above(replace the string dates with your variable as you see fit)

        CultureInfo provider = CultureInfo.InvariantCulture;
        DateTime thedate = DateTime.ParseExact("2019-10-21 22:05:23", "yyyy-MM-dd HH:mm:ss",provider);
        TimeSpan timeSpan = TimeSpan.ParseExact("14:04:41", @"h\:mm\:ss", provider);