JSON.NET Serialize DateTime.MinValue as null

问题:

I'd like DateTime fields that are set to DateTime.MinValue returned by my Web API to be serialized to NULL instead of "0001-01-01T00:00:00".

I understand there's a way to get JSON.NET to omit fields that are set to default values, but I would prefer JSON.NET to specifically serialize DateTime MinValue / "0001-01-01T00:00:00" as null.

Is there a way to do this?

回答1:

Create a custom converter which serializes DateTime.MinValue into null, and (if required) deserializes null into DateTime.MinValue:

public class MinDateTimeConverter : DateTimeConverterBase
{
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (reader.Value == null)
            return DateTime.MinValue;

        return (DateTime)reader.Value;
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        DateTime dateTimeValue = (DateTime)value;
        if (dateTimeValue == DateTime.MinValue)
        {
            writer.WriteNull();
            return;
        }

        writer.WriteValue(value);
    }
}

You can then use attributes to add the converter to your data class, as shown in this example:

public class Example
{
    [JsonConverter(typeof(MinDateTimeConverter))]
    public DateTime ValueOne { get; set; }

    [JsonConverter(typeof(MinDateTimeConverter))]
    public DateTime ValueTwo { get; set; }
}

public static void Main(string[] args)
{
    Example data = new Example();
    data.ValueOne = DateTime.MinValue;
    data.ValueTwo = DateTime.Now;

    JsonSerializer serializer = new JsonSerializer();

    using (StringWriter writer = new StringWriter())
    {
        serializer.Serialize(writer, data);
        Console.Write(writer.ToString());
    }

    Console.ReadKey();
}

Console output:

{"ValueOne":null,"ValueTwo":"2016-10-26T09:54:48.497463+01:00"}

回答2:

Custom DateTime Json Converter

public class DateTimeConverter : JsonConverter
{   
    public override void WriteJson(JsonWriter jsonWriter, object inputObject,JsonSerializer jsonSerializer)
    {
        // Typecast the input object
        var dateTimeObject = inputObject as DateTime?;

        // Set the properties of the Json Writer
        jsonWriter.Formatting = Newtonsoft.Json.Formatting.Indented;

        if(dateTimeObject == DateTime.MinValue)
            jsonWriter.WriteValue((DateTime?)null);
        else
            jsonWriter.WriteValue(dateTimeObject);
    }


    public override object ReadJson(JsonReader reader,
        Type objectType,
        object existingValue,
        JsonSerializer serializer)
    {
        DateTime? readValue = reader.ReadAsDateTime();

        return (readValue == null) ? DateTime.MinValue : readValue;     

    }


    public override bool CanConvert(Type objectType)
    {
        return typeof(DateTime?).IsAssignableFrom(objectType);
    }
}

Usage:

public class DateTest
{
    [JsonConverterAttribute(typeof(DateTimeConverter))]
    public DateTime? MyDateTime { get; set;}

    [JsonConverterAttribute(typeof(DateTimeConverter))]
    public DateTime? MyDateTime1 { get; set; }
}

void Main()
{
    DateTest dateTest = new DateTest 
    { 
      MyDateTime = DateTime.MinValue, 
      MyDateTime1 = DateTime.MaxValue
    };

    Console.WriteLine(JsonConvert.SerializeObject(dateTest));
}

Result:

{
  "MyDateTime": null,
  "MyDateTime1": "9999-12-31T23:59:59.9999999"
}