JsonSerializer.Deserialize returns an empty object with null properties

Question

I try to parse a response by the OSRM map matching service using the following code (here a .NET Fiddle too; UPDATED with fixed version):

namespace OsrmMapMatch
{
    public class OsrmResponse
    {
        public string code;
        public OsrmLeg[] legs;
    }

    public class OsrmLeg
    {
        public OsrmAnnotation annotation;
    }

    public class OsrmAnnotation
    {
        public uint[] nodes;
    }

    internal class Program
    {
        static async Task Main(string[] args)
        {
            const string HttpClientMapMatch = "HttpClientMapMatch";
            const string OsrmUri = "10.757938,52.437444;10.764379,52.437314;10.770562,52.439067;10.773268,52.436633?overview=simplified&radiuses=50;50;50;50&generate_hints=false&skip_waypoints=true&gaps=ignore&annotations=nodes&geometries=geojson";

            ServiceProvider serviceProvider = new ServiceCollection()
                .AddHttpClient(HttpClientMapMatch, httpClient =>
                {
                    httpClient.BaseAddress = new Uri("https://router.project-osrm.org/match/v1/driving/");
                }).Services.BuildServiceProvider();

            IHttpClientFactory httpClientFactory = serviceProvider.GetService<IHttpClientFactory>();

            HttpClient httpClient = httpClientFactory.CreateClient(HttpClientMapMatch);

            HttpResponseMessage response = await httpClient.GetAsync(OsrmUri);
            if (response.IsSuccessStatusCode) 
            {
                string stringData = await response.Content.ReadAsStringAsync();
                OsrmResponse osrmResponse = JsonSerializer.Deserialize<OsrmResponse>(stringData);
                Console.WriteLine($"OsrmResponse: {JsonSerializer.Serialize(osrmResponse)}");
            }
        }
    }
}

Unfortunately, the returned object is empty, its code and legs properties are null:

I have tried the following change with no success:

JsonSerializerOptions options = new()
{
    PropertyNameCaseInsensitive = true
};
OsrmResponse osrmResponse = JsonSerializer.Deserialize<OsrmResponse>(stringData, options);

What could be the reason for the failing JSON parsing?

How do you debug such problems in general?

I would like to use Microsoft's System.Text.Json and do not want to use Newtonsoft.JSON.

I only need the OSM nodes array at the end, that is why I have omitted other members in the response.

there is a difference between fields and properties and how json serializer work with them — Selvin
– Selvin, Commented Jun 30, 2023 at 14:16
@Selvin you have downvoted my question. Aren't the .Net Fiddle, the simplified test case and the screenshot in my question good enough for you? — Alexander Farber
– Alexander Farber, Commented Jun 30, 2023 at 14:29
Does this answer your question? Newtonsoft.Json serialization returns empty json object — Selvin
– Selvin, Commented Jun 30, 2023 at 14:36
which can be found with simple "c# Newtonsoft fields are empty" google query — Selvin
– Selvin, Commented Jun 30, 2023 at 14:36

Krishna Varma · Accepted Answer · 2023-06-30 14:26:59Z

2

Based on the response, your model should look like below. The simplest way to generate the model is using Visual Studio->Edit->Paste Special->Paste Json as Classes or any other Online tools like json2csharp. Once you update the model your code should work.

public class Annotation
{
    public List<object> nodes { get; set; }
}

public class Geometry
{
    public List<List<double>> coordinates { get; set; }
    public string type { get; set; }
}

public class Leg
{
    public List<object> steps { get; set; }
    public string summary { get; set; }
    public double weight { get; set; }
    public double duration { get; set; }
    public Annotation annotation { get; set; }
    public double distance { get; set; }
}

public class Matching
{
    public double confidence { get; set; }
    public Geometry geometry { get; set; }
    public List<Leg> legs { get; set; }
    public string weight_name { get; set; }
    public double weight { get; set; }
    public double duration { get; set; }
    public double distance { get; set; }
}

public class OsrmResponse
{
    public string code { get; set; }
    public List<Matching> matchings { get; set; }
}

edited Jun 30, 2023 at 14:26

answered Jun 30, 2023 at 14:18

Krishna Varma

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4 Comments

Krishna Varma Over a year ago

@Selvin, I didn't understand your point. the OP post is having incorrect model for the response generated by the end point. once he corrects that, the code should work seamlessly

Selvin Over a year ago

There are already answer on using online code generator ... you may mark it as duplicate ... or wirte the answer by YOURSELF and explain what is wrong with OP code ...

Alexander Farber Over a year ago

That is a good hint with "Paste Json as Classes", thank you, I did not know that. I wonder how to detect this mismatch - because JsonSerializer.Deserialize (and I also tried GetFromJsonAsync) do not throw any exception.

Alexander Farber Over a year ago

Thanks Krishna, your suggestion works well, even with reduced members: dotnetfiddle.net/ImzJFi

RBee · Accepted Answer · 2023-07-03 15:07:20Z

2

Your problem is that the Json you want to serialize is different from what you want to deserialize to. You have to fix the class you want your response to deserialize to.

edited Jul 3, 2023 at 15:07

RBee

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answered Jun 30, 2023 at 14:22

porrokynoa

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2 Comments

Alexander Farber Over a year ago

Is there a way to detect that? There was no exception thrown by the JsonSerializer.Deserialize call

porrokynoa Over a year ago

It is not a problem of the method of desiarization. Published both the external library and that of C#. Your probbleme is how you have declared the classes. The desierialization method gives you NULL because it does not find a correspondence with your Json and for this you cannot get the data.

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