using System;

using System.Data;

using System.Xml;

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Formatting = Newtonsoft.Json.Formatting;

public class Program

{

    public static void Main()

    {

        DataTable table = new DataTable();

        table.Columns.Add("Id");

        table.Columns.Add("Column1");

        table.Columns.Add("Column2");

        table.Columns.Add("Column3");

        table.Rows.Add("1", "value1,value2", "value3", "value4,value5");

        table.Rows.Add("2", "value1", "value2,value3", "value4,value5,value6");

        JsonSerializerSettings settings = new JsonSerializerSettings();

        settings.Converters.Add(new CustomDataTableConverter());

        settings.Formatting = Formatting.Indented;

        string json = JsonConvert.SerializeObject(table, settings);

        Console.WriteLine(json);

    }

}

​

​

class CustomDataTableConverter : JsonConverter

{

    public override bool CanConvert(Type objectType)

    {

        return objectType == typeof(DataTable);

    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)

    {

        DataTable table = (DataTable)value;

        JArray array = new JArray();

        foreach (DataRow row in table.Rows)

        {

            JObject obj = new JObject();

            foreach (DataColumn col in table.Columns)

            {

                if (col.ColumnName == "Id") continue; // skip id column

                if (row[col] != null && row[col] != DBNull.Value)

                {

                    string[] values = row[col].ToString().Split(',');

                    obj.Add(col.ColumnName, JArray.FromObject(values));

                }

                else

                {

                    obj.Add(col.ColumnName, JValue.CreateNull());

                }

            }

            array.Add(obj);

        }

        array.WriteTo(writer);

    }

    public override bool CanRead

    {

        get { return false; }

    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)

    {

        throw new NotImplementedException();

    }

}

​