Not formatting Newtonsoft-deserialized object as JSON

[jupiter144]

This was reproduced using the out-of-the-box WeatherForecast api, that Microsoft gives you as a template, when creating a new api in Visual Studio 2022. NLog successfully deserializes an object that is instantiated and initialized normally. It fails to deserialize, it seems, when the object is created through a Newtonsoft deserialization.

UseNlog is called off of the Host as specified in the wiki. The code

using APITestApp.ErrorResponses;
using Microsoft.AspNetCore.Mvc;
using Newtonsoft.Json;

namespace APITestApp.Controllers
{
    [ApiController]
    [Route("[controller]")]
    public class WeatherForecastController : ControllerBase
    {
        private static readonly string[] Summaries = new[]
        {
            "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
        };

        private const string SampleAPIError = @"        {
            ""apiVersion"": ""/prices/v3"",
            ""error"": {
                ""code"": ""400"",
                ""message"": ""OASValidation OpenAPI-Spec-Validation-Domestic-Prices with resource oas://domestic-prices-v3.yaml: failed with reason: [ERROR - Instance failed to match all required schemas (matched only 1 out of 2): [/allOf/0: Object has missing required properties ([height,length,width])]ERROR - Object has missing required properties ([height,length,width]): []]"",
                ""errors"": [
                    {
                        ""title"": ""OASValidation OpenAPI-Spec-Validation-Domestic-Prices with resource 'oas: //domestic-prices-v3.yaml': failed with reason: '[ERROR - Instance failed to match all required schemas (matched only 1 out of 2): [/allOf/0: Object has missing required properties ([height,length,width])] ERROR - Object has missing required properties ([height,length,width]): []],detail:}]        }    }'""
                    }
                ]
            }
        }";

        private readonly ILogger<WeatherForecastController> _logger;

        public WeatherForecastController(ILogger<WeatherForecastController> logger)
        {
            _logger = logger;
        }

        [HttpGet]
        public IEnumerable<WeatherForecast> Get()
        {
            var wf = Enumerable.Range(1, 5).Select(index => new WeatherForecast
            {
                Date = DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
                TemperatureC = Random.Shared.Next(-20, 55),
                Summary = Summaries[Random.Shared.Next(Summaries.Length)]
            })
            .ToArray();
            _logger.LogDebug("GET method {@wf}", wf);
            //
            var errorObject = JsonConvert.DeserializeObject<APIError>(SampleAPIError);
            _logger.LogDebug("GET method with error: {@errorObject}", errorObject);
            return wf;
        }

        [HttpPost]
        public string ReturnApiError(APIError error)
        {            
            return "ReturnApiError";
        }
    }
}

then

ErrorResponses.zip

outputs

2025-11-28 15:35:04.9641|0|DEBUG|APITestApp.Controllers.WeatherForecastController|GET method {"Date":"11/29/2025", "TemperatureC":25, "TemperatureF":76, "Summary":"Hot"} 2025-11-28 15:35:05.1951|0|DEBUG|APITestApp.Controllers.WeatherForecastController|GET method with error: "APITestApp.ErrorResponses.APIError"

ErrorResponses model attached.

[snakefoot]

When using NLog v6.0.6 with the following code:

        private const string SampleAPIError = @"        {
        ""apiVersion"": ""/prices/v3"",
        ""error"": {
            ""code"": ""400"",
            ""message"": ""OASValidation OpenAPI-Spec-Validation-Domestic-Prices with resource oas://domestic-prices-v3.yaml: failed with reason: [ERROR - Instance failed to match all required schemas (matched only 1 out of 2): [/allOf/0: Object has missing required properties ([height,length,width])]ERROR - Object has missing required properties ([height,length,width]): []]"",
            ""errors"": [
                {
                    ""title"": ""OASValidation OpenAPI-Spec-Validation-Domestic-Prices with resource 'oas: //domestic-prices-v3.yaml': failed with reason: '[ERROR - Instance failed to match all required schemas (matched only 1 out of 2): [/allOf/0: Object has missing required properties ([height,length,width])] ERROR - Object has missing required properties ([height,length,width]): []],detail:}]        }    }'""
                }
            ]
        }
    }";

        public class APIError
        {
            public string ApiVersion { get; set; }
            public ErrorDetail Error { get; set; }
        }

        public class ErrorDetail
        {
            public string Code { get; set; }
            public string Message { get; set; }
            public ErrorItem[] Errors { get; set; }
        }

        public class ErrorItem
        {
            public string Title { get; set; }
        }

            var errorObject = JsonConvert.DeserializeObject<APIError>(SampleAPIError);
            _logger.LogDebug("Doing hard work! {@Action}", errorObject);

Then NLog v6.0.6 produces the following output (Tested on net8 and net48):

2025-11-29 11:15:04.7164|DEBUG|Doing hard work! {"ApiVersion":"/prices/v3", "Error":{"Code":"400", "Message":"OASValidation OpenAPI-Spec-Validation-Domestic-Prices with resource oas://domestic-prices-v3.yaml: failed with reason: [ERROR - Instance failed to match all required schemas (matched only 1 out of 2): [/allOf/0: Object has missing required properties ([height,length,width])]ERROR - Object has missing required properties ([height,length,width]): []]", "Errors":[{"Title":"OASValidation OpenAPI-Spec-Validation-Domestic-Prices with resource 'oas: //domestic-prices-v3.yaml': failed with reason: '[ERROR - Instance failed to match all required schemas (matched only 1 out of 2): [/allOf/0: Object has missing required properties ([height,length,width])] ERROR - Object has missing required properties ([height,length,width]): []],detail:}] } }'"}]}}|ConsoleExample.Runner

Together with this Target Layout:

${longdate}|${level:uppercase=true}|${message:withException=true}|${logger}

Have you tried updating to NLog v6.0.6 ? See also: NLog/NLog#6030

[jupiter144]

I have done the upgrade you point out and when bringing the error model into the same namespace, as you have above, the error outputs as JSON. When the error model classes are in a different namespace that is referenced by the using statement however, the output is from the ToString call.

[jupiter144]

Appears to not have to do with deserialization either, as the code:

[HttpGet] 
public IEnumerable<WeatherForecast> Get() 
{ 
	var wf = Enumerable.Range(1, 5).Select(index => new WeatherForecast { Date = DateOnly.FromDateTime(DateTime.Now.AddDays(index)), TemperatureC = Random.Shared.Next(-20, 55), Summary = Summaries[Random.Shared.Next(Summaries.Length)] }) .ToArray(); 	
	APIError errorObject = new APIError() { Error = new MyError() { Code = "123", Message = "This is my error" } };
	_logger.LogDebug("GET method with error: {@errorObject}", errorObject); 
	return wf; 
}

outputs

2025-11-29 13:40:09.5939|0|DEBUG|APITestApp.Controllers.WeatherForecastController|GET method with error: "APITestApp.ErrorResponses.APIError"

Here's my target tag:

<target xsi:type="File" name="allfile" fileName="C:\Logs\all-${shortdate}.log"
        layout="${longdate}|${event-properties:item=EventId:whenEmpty=0}|${level:uppercase=true}|${logger}|${message} ${exception:format=tostring}" />

[snakefoot]

I need some help to reproduce the problem. Can you provide a small example that fails?

[jupiter144]

Here's something simpler. APIErrorEx is exactly the same as APIError except it's in a different namespace. This code:

using APITestApp.ErrorResponses;
using Microsoft.AspNetCore.Mvc;
using Newtonsoft.Json;

namespace APITestApp.Controllers
{
    [ApiController]
    [Route("[controller]")]
    public class WeatherForecastController : ControllerBase
    {
        private readonly ILogger<WeatherForecastController> _logger;

        public WeatherForecastController(ILogger<WeatherForecastController> logger)
        {
            _logger = logger;
        }

        [HttpGet]
        public string Get()
        {           
            //
            APIErrorEx errorObject = new APIErrorEx()
            {
                ApiVersion = "1.2"
            };
            _logger.LogDebug("GET method error from other namespace: {@errorObject}", errorObject);

            APIError a = new APIError()
            {
                ApiVersion = "2.0"
            };
            _logger.LogDebug("Here's the error from local namespace {@a}", a);
            return "Done";
        }
    }

    public class APIError
    {
        public string ApiVersion { get; set; }
    }
}

outputs

2025-11-29 21:25:53.2508|0|DEBUG|APITestApp.Controllers.WeatherForecastController|GET method error from other namespace: "APITestApp.ErrorResponses.APIErrorEx"

2025-11-29 21:25:53.2880|0|DEBUG|APITestApp.Controllers.WeatherForecastController|Here's the error from local namespace {"ApiVersion":"2.0"}

[snakefoot]

Again please provide a small reproducible example. I tried changing the namespace like this, but still NLog works:

namespace Bingo
{
    public class APIError
    {
        public string ApiVersion { get; set; }
        public ErrorDetail Error { get; set; }
    }

    public class ErrorDetail
    {
        public string Code { get; set; }
        public string Message { get; set; }
        public ErrorItem[] Errors { get; set; }
    }

    public class ErrorItem
    {
        public string Title { get; set; }
    }
}

[jupiter144]

It works with the getter/setters. With plain fields without accessors, the foreign namespace object fails to format. I know there is virtue in using properties as opposed to fields. It's just that this behavior is unpredictable.

[snakefoot]

Yes NLog JSON Serializer only recognizes class-properties.

• How to override JSON formatter
• Custom object reflection to include fields

[snakefoot]

Closing question as answered. See also: https://stackoverflow.com/a/79834407/193178