How can I make Web API serialize DateTime in any object into number of milliseconds since 1970?

Question

In my ASP.NET web service I need all my dates to be serialized to JSON as numbers which represent a number of milliseconds passed since 1970 please. I'm using Newtonsoft.Json serializer. What do I need to do to set it up this way?

UPDATE: the available documentation (http://www.newtonsoft.com/json/help/html/DatesInJSON.htm) only mentions serializing a single object with custom settings, what i am looking for is the default serialization settings that would govern serialization of any object

Answer 1

Off the top of my head I would get the ticks of the 1970 date subtract it from the ticks of the current date then divide by 10000 since there are 10000 ticks in a milisecond. This will give you a number which should be easier to serialize. You could make this an extension method of DateTime. Ticks on MSDN: DateTime.Ticks

Answer 2

Have a look at this excellent blog post on creating your own DateTime converter to deal with your requirement. Example actually shows you creating UnixDateTimeConverter.

Answer 3

I'm not sure if this is the easiest way, but you can create a custom converter for DateTimes, then a custom JsonMediaTypeFormatter which uses that converter.

// This class overrides conversion for DateTime values
public class MyDateConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(DateTime);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        // Your algorithm here
        var customValue = ((DateTime)value).Ticks;
        writer.WriteValue(customValue);
    }
}

// This formatter will create serializers with the above converter injected
public class MyJsonFormatter : JsonMediaTypeFormatter
{
    public override JsonSerializer CreateJsonSerializer()
    {
        var serializer = base.CreateJsonSerializer();
        serializer.Converters.Add(new MyDateConverter());
        return serializer;
    }
}

// Inside your WebApi config code, replace the default formatter with your custom one
var defaultJsonFormatter = config.Formatters.OfType<JsonMediaTypeFormatter>().First();
config.Formatters.Remove(defaultJsonFormatter);
config.Formatters.Insert(0, new MyJsonFormatter());

Answer 4

here is what worked:

public class MyConverter: JsonConverter
{
    public override bool CanConvert(Type type)
    {
        return (type == typeof(DateTime) || type == typeof(DateTime?));
    }
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        return new NotSupportedException("An attempt to read a date using a write-only converter from DateTime -> number of milliseconds since 1970.");
    }

    static readonly long ticksTo1970 = new DateTime(1970, 1, 1).Ticks;

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        if (value is DateTime)
        {
            var date = (DateTime)value;
            var unixDateSpan = new TimeSpan(date.Ticks - ticksTo1970);
            var milliseconds = (long)unixDateSpan.TotalMilliseconds;
            writer.WriteValue(milliseconds);
        }
        else
        {
            throw new NotSupportedException("A value of unexpected type where a DateTime value is expected.");
        }
    }
}

public class BaseApiController : ApiController
{
    [NonAction]
    protected JsonResult<T> MyJson<T>(T data)
    {
        var result = this.Json(data);
        result.SerializerSettings.Converters.Insert(0, new MyConverter());
        return result;
    }   
}