// RE: https://stackoverflow.com/questions/75919806/how-to-specify-default-int-value-for-empty-strings-when-using-csvdatareader-in-c

using System;

using System.Text;

using System.Data;

using CsvHelper;

using CsvHelper.TypeConversion;

using CsvHelper.Configuration;

using CsvHelper.Configuration.Attributes;

using System.IO;

using System.Globalization;

using System.Linq;

public class Program

{

    public static void Main()

    {

      // Construct the datatable

      DataTable dataTable = new DataTable();

      dataTable.Columns.Add(new DataColumn("Name", typeof(string)));

      dataTable.Columns.Add(new DataColumn("Credits", typeof(int)) { DefaultValue = 0 });

      dataTable.Columns.Add(new DataColumn("Notes", typeof(string)));

      dataTable.Columns.Add(new DataColumn("LastLogin", typeof(DateTime)));

      dataTable.Columns.Add(new DataColumn("Balance", typeof(decimal)) { DefaultValue = 0 });

​

      // Prepare CSV content

      StringBuilder sbInput = new StringBuilder();

      sbInput.AppendLine("Name;Credits;Notes;LastLogin;Balance");

      sbInput.AppendLine("Michael;;Good guy;2023-03-28;736.26");

      sbInput.AppendLine("John;3;Bad guy;2023-04-01;-49.25");

​

      // Prepare the configuration

      CsvConfiguration csvConfiguration = new CsvConfiguration(CultureInfo.InvariantCulture)

      {

        NewLine = Environment.NewLine,

        Delimiter = ";",

        //MissingFieldFound = (x) => { }

      };

​

//  CsvHelper.TypeConversion.TypeConverterOptions   TypeConverterFactory.RemoveConverter<int>();

//      TypeConverterFactory.AddConverter<int>(new DefaultNumericConverter<int>());

        // Read the CSV stream

        using (var csvReader = new CsvReader(new StringReader(sbInput.ToString()), csvConfiguration))

        {

            csvReader.Context.TypeConverterCache.RemoveConverter<int>();

            csvReader.Context.TypeConverterCache.AddConverter<int>(new DefaultNumericConverter<int>());

            csvReader.Context.TypeConverterCache.RemoveConverter<decimal>();

            csvReader.Context.TypeConverterCache.AddConverter<decimal>(new DefaultNumericConverter<decimal>());

​

            // Unfortunately, it looks like CsvDataReader treats all values as strings and ignores the TypeConverters for other types. 

            // So... don't use it. https://stackoverflow.com/a/56064792/1690217

            csvReader.Read();

            csvReader.ReadHeader();

            while(csvReader.Read())

            {

                var row = dataTable.NewRow();

                foreach (DataColumn column in dataTable.Columns)

                {

                    row[column.ColumnName] = csvReader.GetField(column.DataType, column.ColumnName);

                }

                dataTable.Rows.Add(row);

            }

        }

        Console.WriteLine(String.Join(",", dataTable.Columns.Cast<DataColumn>().Select(x => x.ColumnName)));

        foreach(DataRow row in dataTable.Rows)

        {

            Console.WriteLine(String.Join(",", row.ItemArray));

        }

    }

}

​

​

    /// <summary>

    /// Converts an <see cref="int"/> or <see cref="decimal"/> to and from a <see cref="string"/>. and treats empty strings as default values

    /// </summary>

    public class DefaultNumericConverter<T> : DefaultTypeConverter

    {

        /// <summary>

        /// Converts the string to an object. int or decimal defaulting to zero.

        /// </summary>

        /// <remarks>Will revert to default implementation for non int or decimal expected types</remarks>

        /// <param name="text">The string to convert to an object.</param>

        /// <param name="row">The <see cref="IReaderRow"/> for the current record.</param>

        /// <param name="memberMapData">The <see cref="MemberMapData"/> for the member being created.</param>

        /// <returns>The object created from the string.</returns>

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

        {

            if (String.IsNullOrWhiteSpace(text))

                return default(T);

            var type = typeof(T);

            if (type == typeof(int))

            {

                if (int.TryParse(text, memberMapData.TypeConverterOptions.NumberStyles ?? NumberStyles.Integer, memberMapData.TypeConverterOptions.CultureInfo, out var i))

                {

                    return i;

                }

            }

            else if (type == typeof(decimal))

            {

                if (decimal.TryParse(text, memberMapData.TypeConverterOptions.NumberStyles ?? NumberStyles.Currency, memberMapData.TypeConverterOptions.CultureInfo, out var m))

                {

                    return m;

                }

            }

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

        }

    }