Question

我希望将我的Web API返回的DateTime字段设置为DateTime.MinValue，并将其序列化为NULL而不是"0001-01-01T00:00:00"。

我知道有一种方法可以让JSON.NET省略设置为默认值的字段，但我更希望JSON.NET能够专门序列化DateTime MinValue / "0001-01-01T00:00:00" as null。

有办法做到这一点吗？

Answer 1

创建一个自定义转换器，将DateTime.MinValue序列化为null，并（如果需要）将null反序列化为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);
    }
}

然后，您可以使用属性将转换器添加到数据类中，如下例所示：

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();
}

控制台输出：

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

Answer 2

自定义DateTime Json转换器

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);
    }
}

<强>用法：

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));
}

<强>结果：

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

JSON.NET将DateTime.MinValue序列化为null

2 个答案: