Can you tell JSON.Net to serialize DateTime as Utc even if unspecified?

Dates in my database are stored as Utc. But when I retreieve them w/ the entity framework they come out as type unspecified.

When JSON.Net serializes them they are not in Utc format. Is there a way to tell JSON.Net to serialize DateTimes as Utc even if their type is not specified as Utc?

Answers:

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Method 1

Set DateTimeZoneHandling on JsonSerializerSettings to Utc. That will convert all dates to UTC before serializing them.

public void SerializeObjectDateTimeZoneHandling()
{
  string json = JsonConvert.SerializeObject(
    new DateTime(2000, 1, 1, 1, 1, 1, DateTimeKind.Unspecified),
    new JsonSerializerSettings
    {
      DateTimeZoneHandling = DateTimeZoneHandling.Utc
    });

  Assert.AreEqual(@"""2000-01-01T01:01:01Z""", json);
}

Documentation: DateTimeZoneHandling setting

Method 2

The response above totally works, and so I used that to create an attribute to convert an API response from PST to UTC.

First I needed to create a JsonConverter

public class UTCDateTimeConverter : Newtonsoft.Json.JsonConverter {
    private TimeZoneInfo pacificZone = TimeZoneInfo.FindSystemTimeZoneById("Pacific Standard Time");
    public override bool CanConvert(Type objectType) {
        return objectType == typeof(DateTime);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer) {
        if (reader.Value == null) return null;
        var pacificTime = DateTime.Parse(reader.Value.ToString());
        return TimeZoneInfo.ConvertTimeToUtc(pacificTime, pacificZone);
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer) {
        writer.WriteValue(TimeZoneInfo.ConvertTimeFromUtc((DateTime) value, pacificZone));
    }
}

Then I had to apply that to the properties that needed to be converted

public class Order{
    [JsonConverter(typeof(UTCDateTimeConverter))]
    public DateTime OrderDate {get;set;}
}

Method 3

As @dez mentioned in a comment, you can “mark” the DateTime objects as UTC directly in .net code right after LOADING them from DB and BEFORE serializing them:

var item = GetItemFromDb(...);

// mark appropriate DateTime fields manually as needed
item.OrderDate = DateTime.SpecifyKind(item.OrderDate, DateTimeKind.Utc);

// now it will be serialized to "2018-10-17T16:21:23.507Z" with the Z at the end
// and javascript will parse it properly and convert to local timezone as needed

Method 4

To me, it was simpler to create the UTC converter for DateTime properties (based on the implementation of the Newtonsoft.Json.Converters.IsoDateTimeConverter).

public class UtcJsonDateTimeConverter : DateTimeConverterBase
{
    private const string DefaultDateTimeFormat = "yyyy'-'MM'-'dd'T'HH':'mm':'ss.FFFFFFFZ";

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        string text;

        if (value is DateTime dateTime)
        {
            text = dateTime.ToString(DefaultDateTimeFormat, CultureInfo.InvariantCulture);
        }
        else
        {
            throw new JsonSerializationException(
                $"Unexpected value when converting date. Expected DateTime or DateTimeOffset, got {value.GetType()}.");
        }

        writer.WriteValue(text);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        bool nullable = objectType == typeof(DateTime?);
        if (reader.TokenType == JsonToken.Null)
        {
            if (!nullable)
            {
                throw new JsonSerializationException($"Cannot convert null value to {objectType}.");
            }

            return null;
        }

        if (reader.TokenType == JsonToken.Date)
        {
            return reader.Value;
        }
        else if (reader.TokenType != JsonToken.String)
        {
            throw new JsonSerializationException($"Unexpected token parsing date. Expected String, got {reader.TokenType}.");
        }

        string date_text = reader.Value.ToString();

        if (string.IsNullOrEmpty(date_text) && nullable)
        {
            return null;
        }

        return DateTime.Parse(date_text, CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal);
    }
}

public class SomeEntity
{

   [JsonProperty(PropertyName = "id", Order = 1)]
   public int ID { get; set; }

   [JsonProperty(PropertyName = "created", Order = 2)]
   [JsonConverter(typeof(UtcJsonDateTimeConverter))]
   public DateTime Created { get; set; }
}

Method 5

I used the accepted answer however applied to the default settings:

        JsonConvert.DefaultSettings = (() =>
        {
            var settings = new JsonSerializerSettings();
            settings.Converters.Add(new StringEnumConverter());
            settings.Formatting = Formatting.Indented;
            settings.DateTimeZoneHandling = DateTimeZoneHandling.Utc;
            return settings;
        });

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0