Newtonsoft deserialize doesn't convert string to DateTime

Question

I am using the Facebook Graph API which is returning a a json object that contains a datetime in a string in the following format: "created_time": "2013-01-25T00:11:02+0000"

The deserialized object contains this datetime: "0001-01-01 00:00:00", which I suppose is the equivalent of null. How can I deserialize the datetime string properly?

Here is my DTO class:

using System;
using System.ComponentModel;
using System.Runtime.Serialization;
using System.Text.Json.Serialization;
using Newtonsoft.Json.Converters;
using project.DTOs;

namespace project.DTOs.Facebook
{
    public class FacebookCommentResponseDto
    {
        [JsonPropertyName("id")]
        public string Id { get; set; }
        [JsonPropertyName("from")]
        public FacebookUserDto From { get; set; }
        [JsonPropertyName("message")]
        public string Message { get; set; }
        [JsonPropertyName("created_time")]
        [JsonConverter(typeof(CustomDateTimeConverter))]
        public DateTime CreatedTime { get; set;}
    }
    internal class CustomDateTimeConverter : IsoDateTimeConverter
    {
        public CustomDateTimeConverter()
        {
            base.DateTimeFormat = "yyyy-MM-ddTH:mm:ss.fffK";
        }
    }
}

This is the code where I deserialize the object:

var result = await response.Content.ReadAsStringAsync();
return JsonConvert.DeserializeObject<T>(result);

That is `ISO 8601` format. If you want a `unix` timestamp (to convert) you could add `date_format=U` as part of your call. [See](https://stackoverflow.com/a/3556188/1797425) there for more about converting the ISO 8601 format. — Trevor, Nov 26 '19 at 19:06
Possibly your format is just off a bit? yyyy-MM-ddTH:mm:ss.fffK --> yyyy-MM-ddTHH:mm:ss.ffK(added an H and remove an f as the format you are expecting seems to have hours in two digits and miliseconds in two as well) — peinearydevelopment, Nov 26 '19 at 19:07
Changing the format by adding the H and removing the f didn't work. How exactly do I add ```date_format=U```? — Mattieeec3, Nov 26 '19 at 19:15
@Mattieeec3 Might not help, but rereading, it should be yyyy-MM-ddTHH:mm:ssK as there are no milliseconds provided. — peinearydevelopment, Nov 26 '19 at 19:19

Marius · Accepted Answer · 2019-11-26T20:33:42.973

In your code you have using Newtonsoft.Json.Converters; and using System.Text.Json.Serialization;. On FacebookCommentResponseDto you use JsonPropertyName which belongs to System.Text but the converter class CustomDateTimeConverter is meant to be used with the Newtonsoft.Json attribute JsonProperty not with the System.Text attribute JsonPropertyName. Hence in your code the converter is never called.

One solution ist to remove using System.Text.Json.Serialization; and replace JsonPropertyName in FacebookCommentResponseDto with JsonProperty. That means you only use Newtonsoft.Json and then the date conversion even works out-of-the-box without a converter. The following test is green:

using Newtonsoft.Json;
using System;
using Xunit;

namespace XUnitTestProject1
{
    public class TimeFormatUnitTest
    {
        [Fact]
        public void ParseCreatedTime()
        {
            var timeString = "2013-01-25T00:11:02+0000";
            var json = "{ \"created_time\": \"" + timeString + "\" }";

            var data = JsonConvert.DeserializeObject<FacebookCommentResponseDto>(json);

            Assert.Equal(DateTime.Parse(timeString), data.CreatedTime);
        }
    }

    public class FacebookCommentResponseDto
    {
        [JsonProperty("created_time")]
        public DateTime CreatedTime { get; set; }
    }
}

Explain why that's needed (the fact that his converter is for Newtonsoft while attributes are for `System.Text.Json`) and you've covered the answer — ColinM, Nov 26 '19 at 20:16
@ColinM Thank you for the suggestion. I edited my post and tried to explain it as well as I can. Feel free to edit it if you think its necessary. — Marius, Nov 26 '19 at 20:35

Rena · Answer 2 · 2019-11-27T06:08:24.977

As Marius said,your converter is for Newtonsoft while attributes are for System.Text.Json.You could change [JsonPropertyName] to [JsonProperty].

Another solution is to custom converter which implements JsonConverter<DateTime> in System.Text.Json:

1.Converter:

public class FacebookCommentResponseDto
{
    [JsonPropertyName("id")]
    public string Id { get; set; }

    [JsonPropertyName("message")]
    public string Message { get; set; }
    [JsonPropertyName("created_time")]
    [JsonConverter(typeof(CustomDateTimeConverter))]
    public DateTime CreatedTime { get; set; }
}
public class CustomDateTimeConverter : JsonConverter<DateTime>
{
    public override DateTime Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        Debug.Assert(typeToConvert == typeof(DateTime));
        return DateTime.Parse(reader.GetString());
    }

    public override void Write(Utf8JsonWriter writer, DateTime value, JsonSerializerOptions options)
    {
        writer.WriteStringValue(value.ToString());
    }
}

2.Deserialize:

var time = "2013-01-25T00:11:02+0000";
var ID = "1001";                    
var result = "{ \"created_time\": \"" + time + "\", \"id\": \"" + ID + "\" }";
var data = System.Text.Json.JsonSerializer.Deserialize<FacebookCommentResponseDto>(result);

Newtonsoft deserialize doesn't convert string to DateTime

2 Answers2