csvhelper mapping a field from a different item in the row

Question

I import records from csv files that do not have the same columns. I am trying to create a mapping that will see if a column is missing and then look into a different column and based on that create a value for the first one.

I tried something like this:

Map(m => m.ImportNo).TypeConverter<PeriodConverter>();
Map(m => m.Period).Optional();

And:

public class PeriodConverter : StringConverter
{
    public override object ConvertFromString(string text, IReaderRow row, MemberMapData memberMapData)
    {
        if (String.IsNullOrWhiteSpace(text))
        {
            if (row.GetField("Period") == "08/2012 - 12/2012")
                return 1;
            else if (row.GetField("Period") == "01/2013 - 06/2013")
                return 2;
            else
                return 0;
        }
        
        return int.Parse(text);
    }
}

But it fails as there is no ImportNo column. On the other hand if i change the code of my mapping to this:

Map(m => m.ImportNo).Optional().TypeConverter<PeriodConverter>();
Map(m => m.Period).Optional();

By adding the Optional() It simply ignores the Type converter i have created. Is there a better way i could write this converter for it to work?

Answer 1

ConvertUsing should work

Map(m => m.ImportNo).ConvertUsing(row =>
{
    if(row.TryGetField("ImportNo", out int importNo))
    {
        return importNo;
    }
    
    if (row.GetField("Period") == "08/2012 - 12/2012")
        return 1;
    else if (row.GetField("Period") == "01/2013 - 06/2013")
        return 2;
    else
        return 0;                 
});
Map(m => m.Period).Optional();