Custom conversions when writing CSV files using CsvHelper

Question

I've been doing some CSV reading and writing lately, and ran across CsvHelper which is fantastic so far. I've ran into one small problem; I use a custom converter when reading the files, but when I write them back out, that format is lost. My CSV format looks like this:

67,1234-1,20150115,750,20150115,1340,549,549,406,0,FRG

The fields 20150115,750 map to a single DateTime field called Start (So, 01/15/2015 7:50 AM). My class map looks like this:

public sealed class DutyMap : CsvClassMap<Duty>
{
    static readonly CultureInfo enUS = new CultureInfo("en-US");

    public DutyMap()
    {
        Map(m => m.PersonId).Index(0);
        Map(m => m.DutyName).Index(1);
        Map(m => m.Start).ConvertUsing(row => ParseDate(row.GetField<String>(2), row.GetField<String>(3)));
        Map(m => m.End).ConvertUsing(row => ParseDate(row.GetField<String>(4), row.GetField<String>(5)));
        Map(m => m.DutyTime1).Index(6);
        Map(m => m.DutyTime2).Index(7);
        Map(m => m.FlightTime).Index(8);
        Map(m => m.CreditHours).Index(9);
        Map(m => m.DutyType).Index(10);
    }

    private static DateTime ParseDate(string date, string time)
    {
        DateTime ret;

        if (time.Length < 4)
            time = new String('0', 4 - time.Length) + time;

        if (!DateTime.TryParseExact(date + time, "yyyyMMddHHmm", enUS, DateTimeStyles.None, out ret))
            throw new FormatException(String.Format("Could not parse DateTime.  Date: {0} Time: {1}", date, time));

        return ret;
    }
}

This works great, and I can now call parse an entire file like so:

var csv = new CsvReader(sr);
csv.Configuration.HasHeaderRecord = false;
csv.Configuration.RegisterClassMap<DutyMap>();

Data = csv.GetRecords<Duty>().ToList();

However, when I write the file:

csv.WriteRecords(Data);

The file is written out like so:

67,7454-1,1/15/2015 7:50:00 AM,1/15/2015 1:40:00 PM,549,549,406,0,FPG

Looking through the documentation, I don't see a way to specify a conversation function upon writing, only reading. The only solution I've found so far is to manually write each record by hand:

var csv = new CsvWriter(sw);
foreach (var item in Data)
{
    csv.WriteField(item.PersonId);
    csv.WriteField(item.DutyName);
    csv.WriteField(item.Start.ToString("yyyyMMdd"));
    csv.WriteField(item.Start.ToString("Hmm"));
    csv.WriteField(item.End.ToString("yyyyMMdd"));
    csv.WriteField(item.End.ToString("Hmm"));
    csv.WriteField(item.DutyTime1);
    csv.WriteField(item.DutyTime2);
    csv.WriteField(item.FlightTime);
    csv.WriteField(item.CreditHours);
    csv.WriteField(item.DutyType);

    csv.NextRecord();
}

Is there a better way to do this? Thanks!

Audly

Answer 1

You can do it with a custom type converters (https://github.com/JoshClose/CsvHelper/wiki/Custom-TypeConverter). Just override ConvertToString method.

public class TestConverter : DefaultTypeConverter
{
    public override string ConvertToString(TypeConverterOptions options, object value)
    {
        return base.ConvertToString(options, value);
    }
}

and specify converter when mapping:

Map(m => m.PersonId).Index(0).TypeConverter<TestConverter>();

Upgrowth

Thanks! I started looking at that, but the documentation looked a bit sparse. I'll dig into it more! – Audly

Oh, also would this let me split one field (Start) into two different fields in the CSV file? Remember, I have to split up the date portion and time portion. – Audly

Just use Map statements multiple times with different columns names Map(m => m.PersonId).Index(0).Name("col1"); Map(m => m.PersonId).Index(0).Name("col2"); – Upgrowth

I had to use this code: public override object ConvertFromString(string text, IReaderRow row, MemberMapData memberMapData) – Servitude

Answer 2

If you end up here looking for a way to convert doubles in round-trip compatible format, you can use the below which uses the G17 format.

using (var writer = new StreamWriter("C:/path..."))
using (var csv = new CsvWriter(writer, CultureInfo.InvariantCulture))
{
    csv.Context.TypeConverterOptionsCache.AddOptions<double?>(new TypeConverterOptions 
    { 
        Formats = new string[] { "G17" } 
    });

    csv.WriteRecords(collection);
}

Alansen

The G17 format didn't quite work for me, but I was able to combine it with this answer to get what I needed. – Kendo