JsonSerializer: discriminate the Kind of DateTime objects

Question

I have a dynamic object that contains dates (among other data).

Some of these dates have Kind UTC and others have Kind Local, eg:

var dynamicObject = new 
{
     utcDate = DateTime.UtcNow,    //This one has Kind = DateTimeKind.Utc
     localDate = DateTime.Now      //This one has Kind = DateTimeKind.Local
}

And then I have a JsonSerializer that works as follows:

var isoDateTimeConverter = new IsoDateTimeConverter();
isoDateTimeConverter.DateTimeFormat = "yyyy'-'MM'-'dd'T'HH':'mm':'ss'Z'";
                                            //                       ^
                                            //                  Notice this

var serializerSettings = new JsonSerializerSettings();
SerializerSettings.Converters.Add(isoDateTimeConverter);

var response = context.HttpContext.Response;
var writer = new JsonTextWriter(response.Output) { Formatting = Formatting };

var serializer = JsonSerializer.Create(serializerSettings);
serializer.Serialize(writer, dynamicObject);

writer.Flush();

Which creates a JSON string as this:

{
     "utcDate":"2019-05-02T19:52:20Z",
     "localDate":"2019-05-02T15:52:20Z"
}

This is expected because of how my isoDateTimeConverter is currently defined.

But I'd like to serialize as follows:

{
     "utcDate":"2019-05-02T19:52:20Z",
     "localDate":"2019-05-02T15:52:20"    // <--- no Z
}

Meaning that I'd like to add a 'Z' only when the Kind of the DateTime is Utc.

Is this possible with IsoDateTimeConverter and/or JsonSerializerSettings ?

Answer 1

I would either use IsoDateTimeConverter without setting the DateTimeFormat, which outputs the full DateTime value, with fractions of seconds, and a "Z" if the DateTimeKind is UTC or a time zone offset in "+-HH:mm" format if Local (and the empty string if None).

Otherwise, the K specifier will format the value as you desire, appending the same values for the offset from UTC.

using System;
using Newtonsoft.Json;
using Newtonsoft.Json.Converters;

public class Program
{
    public static void Main(string[] args)
    {
        var dynamicObject = new
        {
            utcDate = DateTime.UtcNow, //This one has Kind = DateTimeKind.Utc
            localDate = DateTime.Now //This one has Kind = DateTimeKind.Local
        }

        ;
        var isoDateTimeConverter = new IsoDateTimeConverter();
        isoDateTimeConverter.DateTimeFormat = "yyyy'-'MM'-'dd'T'HH':'mm':'ssK";
        var serializerSettings = new JsonSerializerSettings();
        serializerSettings.Converters.Add(isoDateTimeConverter);
        var s = new System.Text.StringBuilder();
        using (var w = new System.IO.StringWriter(s))
        using (var writer = new JsonTextWriter(w)
                   {Formatting = Formatting.Indented})
        {
            var serializer = JsonSerializer.Create(serializerSettings);
            serializer.Serialize(writer, dynamicObject);
            writer.Flush();
        }

        Console.WriteLine(s.ToString());
    }
}

dotnetfiddle.

The ISO 8601 format allows for many variations of dates and times, to arbitrary precision. From Wikipedia's article on ISO 8601:

There is no limit on the number of decimal places for the decimal fraction. However, the number of decimal places needs to be agreed to by the communicating parties.