Example of a custom type converter to serialize objects to json strings.

CustomTypeConverter_Example.cs

// 
//       Copyright (C) DataStax, Inc.
// 
//     Please see the license for details:
//     http://www.datastax.com/terms/datastax-dse-driver-license-terms
// 

using System;
using System.ComponentModel;
using System.Reflection;
using Dse;
using Dse.Data.Linq;
using Dse.Mapping;
using Newtonsoft.Json;

namespace myApp
{
    public static class Extensions
    {
        public static T FromJson<T>(this string obj)
        {
            return JsonConvert.DeserializeObject<T>(obj);
        }

        public static string ToJson<T>(this T obj)
        {
            return JsonConvert.SerializeObject(obj);
        }
    }

    public class Programv3
    {
        public static void MainEntry(string[] args)
        {
            var ks = "programv3";
            var session = DseCluster.Builder().AddContactPoint("127.0.0.1").Build().Connect();
            session.CreateKeyspaceIfNotExists(ks);
            session.ChangeKeyspace(ks);
            session.Execute(@"CREATE TABLE IF NOT EXISTS poco ( id BigInt PRIMARY KEY, data BigInt, inner_poco text )");
            var mapConfig = new MappingConfiguration().ConvertTypesUsing(new JsonStringTypeConverter());
            var table = new Table<Poco>(session, mapConfig);
            table.Insert(new Poco { Data = 123, Id = 1, InnerPoco = new InnerPoco { One = 1, Two = "two" } }).Execute();
            var elem = table.First(t => t.Id == 1).Execute();
            Console.WriteLine(JsonConvert.SerializeObject(elem));
            Console.WriteLine("Done");
            Console.ReadLine();
        }

        public class TableColumnTypeConversionRequiredAttribute : Attribute
        {
        }

        [Dse.Mapping.Attributes.Table("poco")]
        public class Poco
        {
            [Dse.Mapping.Attributes.PartitionKey]
            [Dse.Mapping.Attributes.Column("id")]
            public long Id { get; set; }

            [Dse.Mapping.Attributes.Column("data")]
            public long Data { get; set; }

            [Dse.Mapping.Attributes.Column("inner_poco", Type = typeof(string))]
            public InnerPoco InnerPoco { get; set; }
        }
        
        [TableColumnTypeConversionRequired]
        public class InnerPoco
        {
            public long One { get; set; }

            public string Two { get; set; }
        }

        public class JsonStringTypeConverter : Dse.Mapping.TypeConversion.TypeConverter 
        {
            protected override Func<TDatabase, TPoco> GetUserDefinedFromDbConverter<TDatabase, TPoco>()
            {
                TPoco JsonDeserialize(TDatabase db) => db.ToString().FromJson<TPoco>(); 
                return CanConvert<TDatabase, TPoco>() ? (Func<TDatabase, TPoco>) JsonDeserialize : null;
            }

            protected override Func<TPoco, TDatabase> GetUserDefinedToDbConverter<TPoco, TDatabase>()
            {
                TDatabase JsonSerialize(TPoco poco) => (TDatabase)TypeDescriptor.GetConverter(typeof(TDatabase)).ConvertFrom(poco.ToJson());
                return CanConvert<TDatabase, TPoco>() ? (Func<TPoco, TDatabase>) JsonSerialize : null;
            }

            private bool CanConvert<TDatabaseType, TPocoType>()
            {
                return typeof(TDatabaseType) == typeof(string) &&
                       typeof(TPocoType).GetCustomAttribute(typeof(TableColumnTypeConversionRequiredAttribute)) != null;
            }
        }
    }
}