c＃数据库选择然后插入。 但值为0

Question

I am trying to select then insert a datetime from Table 1 to Table 2. I have successfully insert the data. However, the datetime shown in Table 2 is 0000-00-00 00:00:00. Idk where is the error. Someone please help me with this problem. I am struggling with this. And is this the correct way to SELECT then insert ? (Select from Table 1 then INSERT into Table 2)

 try
    {
        string myConnectionString;
        myConnectionString= "server=localhost;uid=root;pwd=root;database=medicloud;SslMode=None;charset=utf8";

        MySqlConnection connection = new MySqlConnection(myConnectionString);
        MySqlCommand cmd = new MySqlCommand();

        cmd.CommandType = CommandType.Text;

        EncodingProvider ppp;
        ppp = CodePagesEncodingProvider.Instance;
        Encoding.RegisterProvider(ppp);

        connection.Open();   

        string select = "Select time from assign where userId=@name";
        cmd.Parameters.AddWithValue("@name", txtValue.Text);                           
        cmd.CommandText = select;
        cmd.Connection = connection;


        MySqlDataReader selectAssign = cmd.ExecuteReader();
        selectAssign.Read();
        string assign = (selectAssign["time"].ToString());
        selectAssign.Close();


        cmd.CommandType = CommandType.Text;
        cmd.CommandText = "INSERT into bluetooth (userId,arm,armNumberDone,armNumber,comDate,assignDate,status) VALUES (@name, @stupid0, @stupid1, @stupid2, @stupid3, @stupid4, @stupid5)";
        cmd.Parameters.AddWithValue("@stupid0", databaseLine);
        cmd.Parameters.AddWithValue("@stupid1", counter);
        cmd.Parameters.AddWithValue("@stupid2", databaseValue);
        cmd.Parameters.AddWithValue("@stupid3", DateTime.Now);
        cmd.Parameters.AddWithValue("@stupid4", assign);
        cmd.Parameters.AddWithValue("@stupid5", complete);
        cmd.Connection = connection;


        cmd.ExecuteNonQuery();
        connection.Close();

    }

    catch (MySqlException ex)
    {
        txtExercise.Text = ex.ToString();
    }

Answer 1

Please try with this

try
{
      string myConnectionString;
      myConnectionString = "server=localhost;uid=root;pwd=root;database=medicloud;SslMode=None;charset=utf8";

      MySqlConnection connection = new 
           MySqlConnection(myConnectionString);
      MySqlCommand cmd = new MySqlCommand();

      cmd.CommandType = CommandType.Text;

      EncodingProvider ppp;
      ppp = CodePagesEncodingProvider.Instance;
      Encoding.RegisterProvider(ppp);

      connection.Open();

      string select = "Select time from assign where userId=@name";
      cmd.Parameters.AddWithValue("@name", txtValue.Text);
      cmd.CommandText = select;
      cmd.Connection = connection;

      MySqlDataReader selectAssign = cmd.ExecuteReader();
      selectAssign.Read();
      string assign = (selectAssign["time"].ToString());
      selectAssign.Close();

      DateTime assignDate = DateTime.Now;
      DateTime.TryParseExact(assign, out assignDate);

      cmd.CommandType = CommandType.Text;
      cmd.CommandText = "INSERT into bluetooth 
(userId,arm,armNumberDone,armNumber,comDate,assignDate,status) VALUES (@name, 
@stupid0, @stupid1, @stupid2, @stupid3, @stupid4, @stupid5)";
      cmd.Parameters.AddWithValue("@stupid0", databaseLine);
      cmd.Parameters.AddWithValue("@stupid1", counter);
      cmd.Parameters.AddWithValue("@stupid2", databaseValue);
      cmd.Parameters.AddWithValue("@stupid3", DateTime.Now);
      cmd.Parameters.AddWithValue("@stupid4", assignDate);
      cmd.Parameters.AddWithValue("@stupid5", complete);
      cmd.Connection = connection;

      cmd.ExecuteNonQuery();
      connection.Close();
   }
  catch (MySqlException ex)
  {
      txtExercise.Text = ex.ToString();
  }
}

Answer 2

cmd.Parameters.AddWithValue("@stupid3", DateTime.Now.ToString("dd/MM/yyyy HH:mm:ss"));
cmd.Parameters.AddWithValue("@stupid4", GetDateString(assign));

Have a method like this:

public static string GetDateString(string date)
{
    DateTime theDate;
    if (DateTime.TryParseExact(date, "dd/MM/yyyy HH:mm:ss", 
            CultureInfo.InvariantCulture, DateTimeStyles.None, out theDate))
    {
        // the string was successfully parsed into theDate
        return theDate.ToString("dd/MM/yyyy HH:mm:ss");
    }
    else
    {
        // the parsing failed, return some sensible default value
        return string.Empty;
    }
}

Answer 3

You need to use .ExecuteReader() the use .Read() to move to each row in the result set. If you are sure the exactly one row will be returned, use .ExecuteScalar() instead. Research on the difference of both online. Below is an example using .ExecuteReader() .

I also re-wrote to use using statements to simplify a bit but not deviate too much from your original code so you do not need to worry about closing and disposing resources since they inherit from IDisposable and will do that automatically once they exit the using block:

string assign = DateTime.Now.ToString();

string myConnectionString;
    myConnectionString= "server=localhost;uid=root;pwd=root;database=medicloud;SslMode=None;charset=utf8";

string select = "Select time from assign where userId=@name";

using (MySqlConnection con = new MySqlConnection(myConnectionString))
{
    using (MySqlCommand cmd = new MySqlCommand(select))
    {
        cmd.CommandType = CommandType.Text;
        cmd.Connection = con;

        cmd.Parameters.AddWithValue("@name", txtValue.Text);                      

        using (MySqlDataReader cursor = cmd.ExecuteReader())
        {
            while (cursor.Read())
            {
                assign = cursor["time"];
            }
        }
    }

    string insert = "INSERT into bluetooth (userId,arm,armNumberDone,armNumber,comDate,assignDate,status) VALUES (@name, @stupid0, @stupid1, @stupid2, @stupid3, @stupid4, @stupid5)";

    using (MySqlCommand cmd = new MySqlCommand(insert))
    {
        cmd.CommandType = CommandType.Text;
        cmd.Connection = con;

        cmd.Parameters.AddWithValue("@stupid0", databaseLine);
        cmd.Parameters.AddWithValue("@stupid1", counter);
        cmd.Parameters.AddWithValue("@stupid2", databaseValue);
        cmd.Parameters.AddWithValue("@stupid3", DateTime.Now);
        cmd.Parameters.AddWithValue("@stupid4", assign);
        cmd.Parameters.AddWithValue("@stupid5", complete);

        cmd.ExecuteNonQuery();
    }
}