Example of model setup for JSON serialization with extension data

EventRecord.cs

namespace Asseco.Rest.Models
{
    [DataContract]
    public partial class EventRecord 
    {
        [JsonExtensionData]
        internal Dictionary<string, object> udf;

        public EventRecord(string EventKind = default(string))
        {
            this.EventKind = EventKind;
            udf = new Dictionary<string, object>();        
        }

        [DataMember(Name = "event-kind")]
        public string EventKind { get; set; }
  
        [DataMember(Name = "version")]
        public int? Version { get; set; }

        [DataMember(Name = "occurred-on")]
        public DateTime? OccurredOn { get; set; }

        [DataMember(Name = "event-id")]
        public Guid? EventId { get; set; }

        [DataMember(Name = "aggregate-kind")]
        public string AggregateKind { get; set; }

        [DataMember(Name = "aggregate-id")]
        public string AggregateId { get; set; }

        [DataMember(Name = "customer-number")]
        public string CustomerNumber { get; set; }

        [DataMember(Name = "sync-timestamp")]
        public string SyncTimestamp { get; set; }
        
        //convenient access to udf fields
        public object this[string key]
        {
            get
            {
                // If this key is in the dictionary, return its value.
                object tmp;
                if (udf.TryGetValue(key, out tmp))
                {
                    return tmp;
                }
                else
                {
                    return null;
                }
            }

            set
            {
                // If this key is in the dictionary, change its value. 

                if (udf.ContainsKey(key))
                {
                    // The key was found; change its value.
                    udf[key] = value;
                }
                else
                {
                    // This key is not in the dictionary; add this key/value pair.
                    udf.Add(key, value);
                }
            }
        }
    }
}