How do I deserialize a nested JSON object which is a string in System.Text.Json?

Question

I'm deserializing JSON in a ASP.NET 5 MVC application using:

var tulemus = JsonSerializer.Deserialize<EstoJarelMaksTulemnus>(apiResponse, new JsonSerializerOptions { PropertyNameCaseInsensitive = true });

public class EstoJarelMaksTulemnus
{
   public string[] Errors { get; set; }
   public EstoData Data { get; set; }
   public string Mac { get; set; }
}

public class EstoData
{
   public string Id { get; set; }
   public string Status { get; set; }
   public string Purchase_url { get; set; }
   public string Merchant_reference { get; set; }
   public decimal Amount { get; set; }
   public string Currency { get; set; }
   public bool Is_test { get; set; }
   public string Return_url { get; set; }
   public string Notification_url { get; set; }
}

This throws the error:

System.Text.Json.JsonException: The JSON value could not be converted to Store.Controllers.CheckoutController+EstoData. Path: $.data | LineNumber: 0 | BytePositionInLine: 497. at System.Text.Json.ThrowHelper.ThrowJsonException_DeserializeUnableToConvertValue(Type propertyType) ...

apiResponse is a single line string, containing an embedded EstoData:

{"errors":[],"data":"{\"id\":\"iUW3YiDIz5Ahg5eO8hV7d3Cv7SVbZ913\",\"status\":\"CREATED\",\"purchase_url\":\"https:\\\/\\\/user.esto.com\\\/application\\\/iUW3YiDIeO8hV7d3Cv7SVbZ913\",\"merchant_reference\":\"15502\",\"amount\":93.95,\"currency\":\"EUR\",\"is_test\":true,\"return_url\":\"http:\\\/\\\/localhost:54274\\\/CheckoutController\\\/EstoJarelmaksOK?tellimus=104742\",\"notification_url\":\"http:\\\/\\\/localhost:54274\\\/CheckoutController\\\/EstoJarelmaksTeade?tellimus=104742\"}","mac":"E9C3E61FC347D8043ABDCF464D537C37A609EC878F95B5F526271A2287F2D2E507B5A14FA3AF5F7A6D4CDECB6E8A1DBDF9A5633E0B3AD96DA35FA1C9"}

Position 497 seems to point to the end of the Data property before mac.

How can I deserialize this JSON to EstoJarelMaksTulemnus, considering EstoData is a concrete nested type in my object but a string in the JSON?

I have seen like a dozen questions about this in the past week. Why is everyone writing or consuming APIs that return this format? — CodeCaster
– CodeCaster, Commented Oct 10, 2021 at 19:26

Ermiya Eskandary · Accepted Answer · 2021-10-09 11:59:49Z

You need to create a custom JsonConverter<T>, where T is EstoData in this case, to be able to correctly deserialise the nested Data JSON object.

This should work, both for deserialisation and serialisation of the object again:

StringToEstoDataConverter.cs

public class StringToEstoDataConverter : JsonConverter<EstoData>
{
  public override EstoData? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
  {
      using (var jsonDoc = JsonDocument.ParseValue(ref reader))
      {
          var infoData = jsonDoc.RootElement.GetString();
          if (infoData != null)
              return JsonSerializer.Deserialize<EstoData>(infoData, options);
      }

      return default;
  }

  public override void Write(Utf8JsonWriter writer, EstoData value, JsonSerializerOptions options)
  {
      JsonSerializer.Serialize(writer, value, value.GetType(), options);
  }
}

EstoJarelMaksTulemnus.cs

public class EstoJarelMaksTulemnus
{
  public string[] Errors { get; set; }

  [JsonConverter(typeof(StringToEstoDataConverter))]
  public EstoData Data { get; set; }

  public string Mac { get; set; }
}

Usage:

var tulemus = JsonSerializer.Deserialize<EstoJarelMaksTulemnus>(apiResponse, new JsonSerializerOptions { PropertyNameCaseInsensitive = true });

Here's a working demo:

public class Program
{
  public static void Main()
  {
      var data =
          "{\"errors\":[],\"data\":\"{\\\"id\\\":\\\"iUW3YiDIz5Ahg5eO8hV7d3Cv7SVbZ913\\\",\\\"status\\\":\\\"CREATED\\\",\\\"purchase_url\\\":\\\"https:\\\\\\/\\\\\\/user.esto.ee\\\\\\/application\\\\\\/iUW3YiDIz5Ahg5eO8hV7d3Cv7SVbZ913\\\",\\\"merchant_reference\\\":\\\"158502\\\",\\\"amount\\\":93.95,\\\"currency\\\":\\\"EUR\\\",\\\"is_test\\\":true,\\\"return_url\\\":\\\"http:\\\\\\/\\\\\\/localhost:54274\\\\\\/CheckoutController\\\\\\/EstoJarelmaksOK?tellimus=104742\\\",\\\"notification_url\\\":\\\"http:\\\\\\/\\\\\\/localhost:54274\\\\\\/CheckoutController\\\\\\/EstoJarelmaksTeade?tellimus=104742\\\"}\",\"mac\":\"E9C3E61FC347D80200F542C43ABDCF464D537C37A609EC878F95B5F526271A2287F2D2E507B5A14FA3AF5F7A6D4CDECB6E8A1DBDF9A5633E0B3AD96DA35FA1C9\"}";


      var tulemus = JsonSerializer.Deserialize<EstoJarelMaksTulemnus>(data, new JsonSerializerOptions { PropertyNameCaseInsensitive = true });

      Console.WriteLine(tulemus.Errors.Length);
      Console.WriteLine(tulemus.Data.Id);
      Console.WriteLine(tulemus.Data.Status);
      Console.WriteLine(tulemus.Data.Purchase_url);
      Console.WriteLine(tulemus.Data.Merchant_reference);
      Console.WriteLine(tulemus.Data.Amount);
      Console.WriteLine(tulemus.Data.Currency);
      Console.WriteLine(tulemus.Data.Is_test);
      Console.WriteLine(tulemus.Data.Return_url);
      Console.WriteLine(tulemus.Data.Notification_url);
      Console.WriteLine(tulemus.Mac);
  }
}

public class StringToEstoDataConverter : JsonConverter<EstoData>
{
  public override EstoData? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
  {
      using (var jsonDoc = JsonDocument.ParseValue(ref reader))
      {
          var infoData = jsonDoc.RootElement.GetString();
          if (infoData != null)
              return JsonSerializer.Deserialize<EstoData>(infoData, options);
      }

      return default;
  }

  public override void Write(Utf8JsonWriter writer, EstoData value, JsonSerializerOptions options)
  {
      JsonSerializer.Serialize(writer, value, value.GetType(), options);
  }
}


public class EstoJarelMaksTulemnus
{
  public string[] Errors { get; set; }

  [JsonConverter(typeof(StringToEstoDataConverter))]
  public EstoData Data { get; set; }

  public string Mac { get; set; }
}

public class EstoData
{
  public string Id { get; set; }
  public string Status { get; set; }
  public string Purchase_url { get; set; }
  public string Merchant_reference { get; set; }
  public decimal Amount { get; set; }
  public string Currency { get; set; }
  public bool Is_test { get; set; }
  public string Return_url { get; set; }
  public string Notification_url { get; set; }
}

Output:

0
iUW3YiDIz5Ahg5eO8hV7d3Cv7SVbZ913
CREATED
https://user.esto.ee/application/iUW3YiDIz5Ahg5eO8hV7d3Cv7SVbZ913
158502
93.95
EUR
True
http://localhost:54274/CheckoutController/EstoJarelmaksOK?tellimus=104742
http://localhost:54274/CheckoutController/EstoJarelmaksTeade?tellimus=104742
E9C3E61FC347D80200F542C43ABDCF464D537C37A609EC878F95B5F526271A2287F2D2E507B5A14FA3AF5F7A6D4CDECB6E8A1DBDF9A5633E0B3AD96DA35FA1C9

Serge · Accepted Answer · 2021-10-09 14:14:21Z

"data" property in your original json is double serialized, so it should be deserialized the second time from json string to object

so try this code

var json=...your json;

var jd = JsonSerializer.Deserialize<Root>(json, new JsonSerializerOptions { PropertyNameCaseInsensitive = true });

// the second deserialize data property from json string to instance
var jdd= JsonSerializer.Deserialize<Data>(jd.data);

JsonDeserialized result = new JsonDeserialized {errors=jd.errors, data=jdd, mac=jd.mac};

var jsonFixed=JsonSerializer.Serialize(result);

fixed json

{
  "errors": [],
  "data": {
    "id": "iUW3YiDIz5Ahg5eO8hV7d3Cv7SVbZ913",
    "status": "CREATED",
    "purchase_url": "https://user.esto.ee/application/iUW3YiDIz5Ahg5eO8hV7d3Cv7SVbZ913",
    "merchant_reference": "158502",
    "amount": 93.95,
    "currency": "EUR",
    "is_test": true,
    "return_url": "http://localhost:54274/CheckoutController/EstoJarelmaksOK?tellimus=104742",
    "notification_url": "http://localhost:54274/CheckoutController/EstoJarelmaksTeade?tellimus=104742"
  },
  "mac": "E9C3E61FC347D80200F542C43ABDCF464D537C37A609EC878F95B5F526271A2287F2D2E507B5A14FA3AF5F7A6D4CDECB6E8A1DBDF9A5633E0B3AD96DA35FA1C9"
}

Test

JsonDeserialized deserializedFixedJson = Deserialize<JsonDeserialized>(jsonFixed, new JsonSerializerOptions { PropertyNameCaseInsensitive = true });

classes

public class JsonDeserialized
{
    public List<object> errors { get; set; }
    public Data data { get; set; }
    public string mac { get; set; }
}
public class Data
{
    public string id { get; set; }
    public string status { get; set; }
    public string purchase_url { get; set; }
    public string merchant_reference { get; set; }
    public double amount { get; set; }
    public string currency { get; set; }
    public bool is_test { get; set; }
    public string return_url { get; set; }
    public string notification_url { get; set; }
}
public class Root
{
    public List<object> errors { get; set; }
    public string data { get; set; }
    public string mac { get; set; }
}

Fatemeh Mansoor · Accepted Answer · 2021-10-09 11:34:24Z

0

the Data in apiResponse is not an object, it's a string , you can convert the string into a model using Newtonsoft Json.Net , as is explained in this issue : Deserializing stringified (quote enclosed) nested objects with Newtonsoft Json.Net

answered Oct 9, 2021 at 11:34

Fatemeh Mansoor

5653 silver badges17 bronze badges

2 Comments

Andrus Over a year ago

Application is using currently only .NET5 JsonSerializer. Is it reasonable to use two serializers in same application or can this solved using .NET own Deserializer ?

Ermiya Eskandary Over a year ago

@Andrus It is doable using a temporary object in between or using a JsonConverter which I've outlined below - you can use 2 serializer but in this case, it would be overkill

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