How to write only selected class fields into CSV with CsvHelper?

Question

I use CsvHelper to read and write CSV files and it is great, yet I don't understand how to write only selected type fields.

Say we had:

using CsvHelper.Configuration;

namespace Project
{
    public class DataView
    {
        [CsvField(Name = "N")]
        public string ElementId { get; private set; }

        [CsvField(Name = "Quantity")]
        public double ResultQuantity { get; private set; }

        public DataView(string id, double result)
        {
            ElementId = id;
            ResultQuantity = result;
        }
    }
}

and we wanted to exclude "Quantity" CsvField from resulting CSV file that we currently generate via something like:

using (var myStream = saveFileDialog1.OpenFile())
{
    using (var writer = new CsvWriter(new StreamWriter(myStream)))
    {
        writer.Configuration.Delimiter = '\t';
        writer.WriteHeader(typeof(ResultView));
        _researchResults.ForEach(writer.WriteRecord);
    }
}

What could I use to dynamically exclude a type field from the CSV?

If it is necessary we could process the resulting file, yet I do not know how to remove an entire CSV column with CsvHelper.

Answer 1

I recently needed to achieve a similar result by determining what fields to include at runtime. This was my approach:

1. Create a mapping file to map which fields I need at runtime by passing in an enum into the class constructor

   public sealed class MyClassMap : CsvClassMap<MyClass>
   {
       public MyClassMap(ClassType type)
       {
           switch (type)
           {
               case ClassType.TypeOdd
                   Map(m => m.Field1);
                   Map(m => m.Field3);
                   Map(m => m.Field5);                 
                   break;
               case ClassType.TypeEven:
                   Map(m => m.Field2);
                   Map(m => m.Field4);
                   Map(m => m.Field6);                 
                   break;
               case ClassType.TypeAll:
                   Map(m => m.Field1);
                   Map(m => m.Field2);
                   Map(m => m.Field3);
                   Map(m => m.Field4);
                   Map(m => m.Field5);
                   Map(m => m.Field6);                 
                   break;
           }
       }
   }
   

2. Write out the records to using the mapping configuration

   using (var memoryStream = new MemoryStream())
   using (var streamWriter = new StreamWriter(memoryStream))
   using (var csvWriter = new CsvWriter(streamWriter))
   {
       csvWriter.Configuration.RegisterClassMap(new MyClassMap(ClassType.TypeOdd));
       csvWriter.WriteRecords(records);
       streamWriter.Flush();
       return memoryStream.ToArray();
   }