DataTable转换为CSV日期格式

Question

I'm trying to export a DataTable to CSV, with a number of columns. I would like that the date_time column is exported to CSV while retaining the database date_time format (YYY-MM-DD HH:mm:ss), or something like that.

This is my code:

private void DataTableToCsv(string path, DataTable dt)
        {
            File.Delete(path);
            StringBuilder sb = new StringBuilder();

            string[] columnNames = dt.Columns.Cast<DataColumn>().
                                              Select(column => column.ColumnName).
                                              ToArray();
            sb.AppendLine(string.Join(",", columnNames));

            foreach (DataRow row in dt.Rows)
            {
                string[] fields = row.ItemArray.Select(field => field.ToString()).
                                                ToArray();
                sb.AppendLine(string.Join(",", fields));
            }

            File.WriteAllText(path, sb.ToString());
        }

The dates are appearing in a different format, which is giving me errors when trying to pick up from MySQL.

Answer 1

I know there is an accepted answer already, but...

Actually there is a way to control the formatting of dates in a consistent manner, without specifying the format for every type of data: you can use IFormatProvider

First, the method object.ToString(); with no parameters is formatting your object using current CultureInfo set in your thread/application/system. This is problematic when you need consistent formatting, for example when you try to save values into database. It isn't only problematic for dates but also for numbers - there are languages out there that use comma as decimal separator or use thousand separator in a number, for example, and databases do not like that very much. Now imagine your program is run on the computer that has a different language set...

Having said that, many of those problems can be avoided by using object.ToString(CultureInfo.InvariantCulture); instead. It is associated with the English language. Then, the result for 31th October 2014will be: 10/31/2014 08:35:52

Obviously still not what you want.

You can further control your formatting by modifying the culture a little yourself:

CultureInfo format = (CultureInfo) CultureInfo.InvariantCulture.Clone();

// those are the formats used by ToString() mathod:
format.DateTimeFormat.ShortDatePattern = "yyyy-MM-dd";
format.DateTimeFormat.ShortTimePattern = "HH:mm:ss";

Console.WriteLine(DateTime.Now.ToString(format));

double ddd=13.11;
Console.WriteLine(ddd.ToString(format));

string sss = "some string";
// although this may not be a good idea:
Console.WriteLine(sss.ToString(format));

result:

2014-10-31 08:39:53
13.11
some string

Answer 2

With DateTime values, you can control the output by calling

dateTimeField.ToString("yyyy-dd-MM");

Currently you're treating all fields equally, and using the default conversion:

field => field.ToString()

You can't specify a conversion as object.ToString() has no overloads to do so; you'd have to specify what conversion to use for each type separately, ie:

string[] fields = row.ItemArray.Select(field => ConvertToCsvValue(field)).ToArray();

and

static void ConvertToCsvValue(object value)
{
    if (value is DateTime)
    {
        return ((DateTime)value).ToString("yyyy-dd-MM");
    }
    else
    {
        return value.ToString();
    }
}

Answer 3

data in a database is not aware of any format; the behaviour you are experiencing is related to that and is correct.
when filling the csv your code is taking the default format for the env/os/locale and applying it to the values.

to solve the issue you have some possible solution:

• you change the source sql code to produce a sql text field filled with formatted data (imho a bad choice)

• you handle the format client side when preparing the csv; you have to modify your code to handle the fields one by one applying the correct format to date fields

• you alter the datatable content applying the expected format to date fields (this may be possible or maybe not depending on datatype of the involved fields)

my preference goes to the second or third solution because i prefer to keep formatting on the client side but YMMV and in your post there is not enough information to make a proper choice.