using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.IO;

using System.Data;

using System.ComponentModel.DataAnnotations;

using System.Globalization;

using System.Reflection;

using System.Collections.ObjectModel;

​

using NUnit.Framework; // Throws NUnit.Framework.AssertionException

​

using CsvHelper;

using CsvHelper.Configuration;

using CsvHelper.Configuration.Attributes;

using CsvHelper.Expressions;

using CsvHelper.TypeConversion;

​

using Newtonsoft.Json;

​

//https://stackoverflow.com/questions/72196798/trying-to-implement-a-type-converter-for-csvhelper-has-no-effect

​

    public class NullDecimalConverter : DecimalConverter

    {

        public override object ConvertFromString(string text, IReaderRow row, MemberMapData mapData)

        {

            if (text == "NULL") return null;

            return base.ConvertFromString(text, row, mapData);

        }

    }

​

    public class Model

    {

        public decimal? Score{ get; set; }      

    }

​

    public class ScoreMapping : ClassMap<Model>

    {

        public ScoreMapping()

        {

            Map(m => m.Score).Name("sub_score");

        }

    }

​

    class TestClass

    {

        public static void Test()

        {

            var csvString = "sub_score\n1.1\n2.2\nNULL";

            var config = new CsvConfiguration(CultureInfo.InvariantCulture);

            Console.WriteLine(csvString);

            using (var reader = new StringReader(csvString))

            using (var csv = new CsvReader(reader, CultureInfo.InvariantCulture))

            {

                csv.Context.RegisterClassMap<ScoreMapping>();

                csv.Context.TypeConverterCache.AddConverter<decimal>(new NullDecimalConverter());

                var records = csv.GetRecords<Model>().ToList();

                records.Dump();

                Assert.IsTrue(new decimal?[] { 1.1M, 2.2M, null }.SequenceEqual(records.Select(m => m.Score)));

            }

        }   

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: {0} ({1})", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , Environment.Version);

            Console.WriteLine("OS Version: {0}, NewLine: {1}", System.Environment.OSVersion, JsonConvert.SerializeObject(Environment.NewLine));

            Console.WriteLine("{0} version: {1}", typeof(CsvReader).Assembly.GetName().Name,  typeof(CsvReader).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

                Console.WriteLine("Failed with unhandled exception: ");

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​

#if false       

        public override string ConvertToString(object value, IWriterRow row, MemberMapData memberMapData)

        {

            if (value == null)

            {

                return "NULL";

            }

            return base.ConvertToString(value, row, memberMapData);

        }

#endif      

​