如何在 asp.net-core 6.0 中构建 DateOnlyJsonConverter

Question

Like many others already had the problem, I'm having problem with serializing a JSON from string/object to DateOnly.

I had already tried to implement solutions that were given in these posts. I also use Newtonsoft.Json .

https://github.com/JamesNK/Newtonsoft.Json/issues/2521

Thats my current DTO

using Newtonsoft.Json;
using JsonSerializer = Newtonsoft.Json.JsonSerializer;

namespace ......;

public class PostDto
{
    public PostDto(
        DateOnly postDate
    )
    {
        PostDate = postDate;
    }

    [JsonConverter(typeof(DateOnlyJsonConverter))]
    public DateOnly PostDate { get; }
}

If I build the converter like this, I get the problem that reader.Value can be null. If I bypass the warning, which I do, I get this error.

public class DateOnlyJsonConverter : JsonConverter<DateOnly>
{
    private const string Format = "yyyy-MM-dd";

    public override void WriteJson(JsonWriter writer, DateOnly value, JsonSerializer serializer) =>
        writer.WriteValue(value.ToString(Format, CultureInfo.InvariantCulture));

    public override DateOnly ReadJson(
        JsonReader reader, Type objectType, DateOnly existingValue, bool hasExistingValue,
        JsonSerializer serializer) => DateOnly.ParseExact(((string)
        reader.Value)!, Format, CultureInfo.InvariantCulture);
}

System.ArgumentNullException: Value cannot be null. (Parameter 's') at System.DateOnly.ParseExact(String s, String format, IFormatProvider provider, DateTimeStyles style)

The JSON I am Posting

   "postDate": {
      "year": 2020,
      "month": 10,
      "day": 10,
      "dayOfWeek": 0
    },

Program.cs

builder.Services.AddControllers().AddNewtonsoftJson();

Answer 1

To use the converter from this answer you need to post data in correct format. The this DateOnlyJsonConverter specifies it "yyyy-MM-dd" so your post body should look like:

{
   "postDate": "2020-10-10"
}