using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Runtime.Serialization.Formatters;

using System.IO;

using System.Data;

using System.ComponentModel.DataAnnotations;

using System.Globalization;

using System.Reflection;

​

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Converters;

using Newtonsoft.Json.Serialization;    

​

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

​

    //https://stackoverflow.com/questions/53695270/custom-object-serialization-vs-preservereferenceshandling#comment94247797_53695270

​

    public abstract class ReferenceHandlingCustomCreationConverter<T> : JsonConverter where T : class

    {

        const string refProperty = "$ref";

        const string idProperty = "$id";

​

        public override bool CanConvert(Type objectType)

        {

            return typeof(T).IsAssignableFrom(objectType);

        }

​

        protected virtual T Create(Type objectType, T existingValue, JsonSerializer serializer, JObject obj)

        {

            return existingValue ?? (T)serializer.ContractResolver.ResolveContract(objectType).DefaultCreator();

        }

​

        protected abstract void Populate(JObject obj, T value, JsonSerializer serializer);

​

        protected abstract void WriteProperties(JsonWriter writer, T value, JsonSerializer serializer, JsonObjectContract contract);

​

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

        {

            var contract = serializer.ContractResolver.ResolveContract(objectType);

            if (!(contract is JsonObjectContract))

            {

                throw new JsonSerializationException(string.Format("Invalid non-object contract type {0}", contract));

            }

            if (!(existingValue == null || existingValue is T))

            {

                throw new JsonSerializationException(string.Format("Converter cannot read JSON with the specified existing value. {0} is required.", typeof(T)));

            }

​

            if (reader.MoveToContent().TokenType == JsonToken.Null)

                return null;

            var obj = JObject.Load(reader);

​

            var refId = (string)obj[refProperty].RemoveFromLowestPossibleParent();

            var objId = (string)obj[idProperty].RemoveFromLowestPossibleParent();

            if (refId != null)

            {

                var reference = serializer.ReferenceResolver.ResolveReference(serializer, refId);

                if (reference != null)

                    return reference;

            }

​

            var value = Create(objectType, (T)existingValue, serializer, obj);

​

            if (objId != null)

            {

                // Add the empty array into the reference table BEFORE poppulating it, to handle recursive references.

                serializer.ReferenceResolver.AddReference(serializer, objId, value);

            }

​

            Populate(obj, value, serializer);

​

            return value;

        }

​

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

        {

            var contract = serializer.ContractResolver.ResolveContract(value.GetType());

            if (!(contract is JsonObjectContract))

            {

                throw new JsonSerializationException(string.Format("Invalid non-object contract type {0}", contract));

            }

            if (!(value is T))

            {

                throw new JsonSerializationException(string.Format("Converter cannot read JSON with the specified existing value. {0} is required.", typeof(T)));

            }

​

            writer.WriteStartObject();

​

            if (serializer.ReferenceResolver.IsReferenced(serializer, value))

            {

                writer.WritePropertyName(refProperty);

                writer.WriteValue(serializer.ReferenceResolver.GetReference(serializer, value));

            }

            else

            {

                writer.WritePropertyName(idProperty);

                writer.WriteValue(serializer.ReferenceResolver.GetReference(serializer, value));

​

                WriteProperties(writer, (T)value, serializer, (JsonObjectContract)contract);

            }

​

            writer.WriteEndObject();

        }

    }

​

    public static partial class JsonExtensions

    {

        public static JsonReader MoveToContent(this JsonReader reader)

        {

            if (reader.TokenType == JsonToken.None)

                reader.Read();

            while (reader.TokenType == JsonToken.Comment && reader.Read())

                ;

            return reader;

        }

​

        public static JToken RemoveFromLowestPossibleParent(this JToken node)

        {

            if (node == null)

                return null;

            var contained = node.AncestorsAndSelf().Where(t => t.Parent is JContainer && t.Parent.Type != JTokenType.Property).FirstOrDefault();

            if (contained != null)

                contained.Remove();

            // Also detach the node from its immediate containing property -- Remove() does not do this even though it seems like it should

            if (node.Parent is JProperty)

                ((JProperty)node.Parent).Value = null;

            return node;

        }

    }

​

    public class DefaultReferenceHandlingCustomCreationConverter<T> : ReferenceHandlingCustomCreationConverter<T> where T : class

    {

        protected override void Populate(JObject obj, T value, JsonSerializer serializer)

        {

            using (var reader = obj.CreateReader())

                serializer.Populate(reader, value);

        }

​

        protected override void WriteProperties(JsonWriter writer, T value, JsonSerializer serializer, JsonObjectContract contract)

        {

            foreach (var property in contract.Properties.Where(p => p.Writable && !p.Ignored))

            {

                // TODO: handle JsonProperty attributes including

                // property.Converter, property.IsReference, property.ItemConverter, property.ItemReferenceLoopHandling, 

                // property.ItemReferenceLoopHandling, property.ObjectCreationHandling, property.ReferenceLoopHandling, property.Required                            

                var itemValue = property.ValueProvider.GetValue(value);

                writer.WritePropertyName(property.PropertyName);

                serializer.Serialize(writer, itemValue);

            }

        }

    }

​

    public class RootObject

    {

        public RootObject() { this.Children = new List<RootObject>(); }

​

        public string A { get; set; }

        public string B { get; set; }

​

        public List<RootObject> Children { get; set; }

    }

​

    class TestClass

    {

        public static void Test()

        {

            var parent = new RootObject()

            {

                A = "Parent A",

                B = "Parent B",

            };

​

            var child = new RootObject

            {

                A = "Child A",

                B = "Child B",

            };

​

            parent.Children.AddRange(new[] { parent, child, child, parent, child });

            child.Children.AddRange(new[] { parent, child });

​

            var settings = new JsonSerializerSettings

            {

                Converters = { new DefaultReferenceHandlingCustomCreationConverter<RootObject>() },

                ReferenceLoopHandling = ReferenceLoopHandling.Serialize,

            };

            var json = JsonConvert.SerializeObject(parent, Formatting.Indented, settings);

​

            Console.WriteLine(json);

​

            var parent2 = JsonConvert.DeserializeAnonymousType(json, parent, settings);

​

            var json2 = JsonConvert.SerializeObject(parent2, Formatting.Indented, settings);

​

            Assert.IsTrue(json == json2);

​

            Assert.IsTrue(parent.Children.Distinct().Count() == parent2.Children.Distinct().Count());

​

            Assert.IsTrue(parent.Children.Select(c => c == parent).SequenceEqual(parent2.Children.Select(c => c == parent2)));

​

        }

    }

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: " + Environment.Version);

            Console.WriteLine("Json.NET version: " + typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

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

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​