questions/29449641/deserialize-json-when-type-can-be-different#29449760

CSharp · Console

/Program.cs

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 Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using Newtonsoft.Json.Converters;
using Newtonsoft.Json.Serialization;	

    // https://stackoverflow.com/questions/29449641/deserialize-json-when-type-can-be-different#29449760

    public class JsonSingleOrEmptyArrayConverter<T> : JsonConverter where T : class
    {
        public override bool CanConvert(Type objectType)
        {
            return typeof(T).IsAssignableFrom(objectType);
        }

        public override bool CanWrite { get { return false; } }

        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            var contract = serializer.ContractResolver.ResolveContract(objectType);
			if (!(contract is Newtonsoft.Json.Serialization.JsonObjectContract || contract is Newtonsoft.Json.Serialization.JsonDictionaryContract))
			{
				throw new JsonSerializationException(string.Format("Unsupported objectType {0} at {1}.", objectType, reader.Path));
			}

            switch (reader.SkipComments().TokenType)
            {
                case JsonToken.StartArray:
                    {
                        int count = 0;
                        while (reader.Read())
                        {
                            switch (reader.TokenType)
                            {
                                case JsonToken.Comment:
                                    break;
                                case JsonToken.EndArray:
                                    return existingValue;
                                default:
                                    {
                                        count++;
                                        if (count > 1)
                                            throw new JsonSerializationException(string.Format("Too many objects at path {0}.", reader.Path));
                                        existingValue = existingValue ?? contract.DefaultCreator();
                                        serializer.Populate(reader, existingValue);
                                    }
                                    break;
                            }
                        }
                        // Should not come here.
                        throw new JsonSerializationException(string.Format("Unclosed array at path {0}.", reader.Path));
                    }

                case JsonToken.Null:
                    return null;

                case JsonToken.StartObject:
                    existingValue = existingValue ?? contract.DefaultCreator();
                    serializer.Populate(reader, existingValue);
                    return existingValue;

                default:
                    throw new InvalidOperationException("Unexpected token type " + reader.TokenType.ToString());
            }
        }

        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            throw new NotImplementedException();
        }
    }

    public static partial class JsonExtensions
    {
        public static JsonReader SkipComments(this JsonReader reader)
        {
            while (reader.TokenType == JsonToken.Comment && reader.Read())
                ;
            return reader;
        }
    }

    // https://stackoverflow.com/questions/29449641/deserialize-json-when-type-can-be-different#29449760
    public class User
    {
        //some other fields...
        [JsonConverter(typeof(JsonSingleOrEmptyArrayConverter<Personal>))]
        public Personal personal { get; set; }
        //some other fields...
    }

    public class Personal
    {
        public byte political { get; set; }
        public string[] langs { get; set; }
        public string religion { get; set; }
        public string inspired_by { get; set; }
        public byte people_main { get; set; }
        public byte life_main { get; set; }
        public byte smoking { get; set; }
        public byte alcohol { get; set; }
    }

    public class TestClass
    {
        public static void Test()
        {
            string json0 = @"{ personal: null }";
            string json1 = @"{ personal: [] }";
            string json2 = @"{
                personal: {
                religion: 'Нет',
                smoking: 1,
                alcohol: 4
                } //when not empty.
            }";

            string json3 = @"{
                personal: [/* Some Comment */{
                religion: 'Нет',
                smoking: 1,
                alcohol: 4
                }/* Some Comment */] //when not empty.
            }";

            string json4 = @"{
                personal: [
                /* Some Comment */{
                religion: 'Нет',
                smoking: 1,
                alcohol: 4
                }/* Some Comment */,
                /* Some Comment */{
                religion: 'Нет',
                smoking: 1,
                alcohol: 4
                }/* Some Comment */,
            ] //when not empty.
            }";

            string json5 = @"{
                personal: [
                /* Some Comment */{
                religion: 'Нет',
                smoking: 1,
                alcohol: 4
                }";

            Test(json0, p => Assert.IsTrue(p == null));
            Test(json1, p => Assert.IsTrue(p == null));
            Test(json2, p => Assert.IsTrue(p != null && p.religion == "Нет"));
            Test(json3, p => Assert.IsTrue(p != null && p.religion == "Нет"));
            try
            {
                Test(json4, p => { throw new AssertionFailedException("Should have failed"); } );
            }
            catch (JsonException ex)
            {
                Console.WriteLine("Caught expected exception: " + ex.Message);
            }

            try
            {
                Test(json5, p => { throw new AssertionFailedException("Should have failed"); });
            }
            catch (JsonException ex)
            {
                Console.WriteLine("Caught expected exception: " + ex.Message);
            }

            Console.WriteLine("Done with tests.");
        }

        static void Test(string json, Action<Personal> validate)
        {
            var user = JsonConvert.DeserializeObject<User>(json);
            var newJson = JsonConvert.SerializeObject(user, Formatting.Indented);
            Console.WriteLine(newJson);

            validate(user.personal);
        }
    }

	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;
			}
		}
	}

    public class AssertionFailedException : System.Exception
    {
        public AssertionFailedException() : base() { }

        public AssertionFailedException(string s) : base(s) { }
    }

    public static class Assert
    {
        public static void IsTrue(bool value)
        {
            IsTrue(value, "failed");
        }

        public static void IsTrue(bool value, string message)
        {
            if (value == false)
                throw new AssertionFailedException(message ?? "failed");
        }
    }