JSON deserialization error when property name is missing

Question

I am trying to consume an external web service and I am using .NET Core and the Flurl framework. I get a response from the service like below:

[
   "Successful Request: 96 Results",
   [
      {
         "eventdate":"2019-10-18",
         "name":"",
         "url":"",
         "info":"",
         "showtime":null,
         "url_tix":"",
         "event_owner":"xxx",
         "follow_url":"xxx",
         "event_image":"xxx",
         "venue":"xxx",
         "city":"xxx",
         "country":"xxx",
         "state":""
      }
   ]
]

and I have a C# entity definition like below:

public class ServiceResponce
{
    public Event[] Events { get; set; }
}

public class Event
{
    [JsonProperty("eventdate")]
    public DateTimeOffset Eventdate { get; set; }

    [JsonProperty("name")]
    public string Name { get; set; }

    [JsonProperty("url")]
    public string Url { get; set; }

    [JsonProperty("info")]
    public string Info { get; set; }

    [JsonProperty("showtime")]
    public object Showtime { get; set; }

    [JsonProperty("url_tix")]
    public object UrlTix { get; set; }

    [JsonProperty("event_owner")]
    public string EventOwner { get; set; }

    [JsonProperty("follow_url")]
    public Uri FollowUrl { get; set; }

    [JsonProperty("event_image")]
    public object EventImage { get; set; }

    [JsonProperty("venue")]
    public string Venue { get; set; }

    [JsonProperty("city")]
    public string City { get; set; }

    [JsonProperty("country")]
    public string Country { get; set; }

    [JsonProperty("state")]
    public string State { get; set; }
}

When I tried to call the Flurl method to consume the web service like below:

var result = await serviceUrl.GetJsonAsync<ServiceResponce>();

I got the error mentioned below:

Cannot deserialize the current JSON array (e.g. [1,2,3]) into type 'xxx.ServiceResponce' because the type requires a JSON object (e.g. {"name":"value"}) to deserialize correctly. To fix this error either change the JSON to a JSON object (e.g. {"name":"value"}) or change the deserialized type to an array or a type that implements a collection interface (e.g. ICollection, IList) like List that can be deserialized from a JSON array. JsonArrayAttribute can also be added to the type to force it to deserialize from a JSON array. Path '', line 1, position 1.

Do you have any solution for that? Any help always is welcome.

I had only get; in the property, because of that also not serialized :( . After adding Set; also into the property def, serialized correctly. Hope It Helps! — HydTechie
– HydTechie, Commented Oct 31, 2021 at 19:52

Brian Rogers · Accepted Answer · 2019-10-14 17:40:05Z

The problem here is the JSON response is actually an array of mixed types. The first element of the array is a string, and the second element is an array of event objects. You will need a custom JsonConverter to deserialize this JSON.

Here is the code you would need for the converter:

class ServiceResponceConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return (objectType == typeof(ServiceResponce));
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        JArray ja = JArray.Load(reader);
        ServiceResponce resp = new ServiceResponce();

        resp.Events = ja[1].ToObject<Event[]>(serializer);

        return resp;
    }

    public override bool CanWrite => false;

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

Then, add a [JsonConverter] attribute to the ServiceResponce class to tie it to the converter:

[JsonConverter(typeof(ServiceResponceConverter))]
public class ServiceResponce
{
    public Event[] Events { get; set; }
}

Now you can deserialize to the ServiceResponce class as normal and it will work properly.

Optional: If you also want to capture the "Successful Request: 96 Results" string from the response, add

public string ResultString { get; set; }

to the ServiceResponce class and add the following line to the the ReadJson method of the converter:

resp.ResultString = (string)ja[0];

Working demo here: https://dotnetfiddle.net/opPUmX

Ahmed Msaouri · Accepted Answer · 2019-10-14 11:05:08Z

I think the problem is in the Json object, I have generated a class with 'Newtonsoft.Json', if you can try this code:

// <auto-generated />
//
// To parse this JSON data, add NuGet 'Newtonsoft.Json' then do:
//
//    using MyNameSpace;
//
//    var event = Event.FromJson(jsonString);

namespace MyNameSpace
{
    using System;
    using System.Collections.Generic;

    using System.Globalization;
    using Newtonsoft.Json;
    using Newtonsoft.Json.Converters;

    public partial class EventClass
    {
        [JsonProperty("eventdate")]
        public DateTimeOffset Eventdate { get; set; }

        [JsonProperty("name")]
        public string Name { get; set; }

        [JsonProperty("url")]
        public string Url { get; set; }

        [JsonProperty("info")]
        public string Info { get; set; }

        [JsonProperty("showtime")]
        public object Showtime { get; set; }

        [JsonProperty("url_tix")]
        public string UrlTix { get; set; }

        [JsonProperty("event_owner")]
        public string EventOwner { get; set; }

        [JsonProperty("follow_url")]
        public string FollowUrl { get; set; }

        [JsonProperty("event_image")]
        public string EventImage { get; set; }

        [JsonProperty("venue")]
        public string Venue { get; set; }

        [JsonProperty("city")]
        public string City { get; set; }

        [JsonProperty("country")]
        public string Country { get; set; }

        [JsonProperty("state")]
        public string State { get; set; }
    }

    public partial struct EventUnion
    {
        public EventClass[] EventClassArray;
        public string String;

        public static implicit operator EventUnion(EventClass[] EventClassArray) => new EventUnion { EventClassArray = EventClassArray };
        public static implicit operator EventUnion(string String) => new EventUnion { String = String };
    }

    public class Event
    {
        public static EventUnion[] FromJson(string json) => JsonConvert.DeserializeObject<EventUnion[]>(json, MyNameSpace.Converter.Settings);
    }

    public static class Serialize
    {
        public static string ToJson(this EventUnion[] self) => JsonConvert.SerializeObject(self, MyNameSpace.Converter.Settings);
    }

    internal static class Converter
    {
        public static readonly JsonSerializerSettings Settings = new JsonSerializerSettings
        {
            MetadataPropertyHandling = MetadataPropertyHandling.Ignore,
            DateParseHandling = DateParseHandling.None,
            Converters =
            {
                EventUnionConverter.Singleton,
                new IsoDateTimeConverter { DateTimeStyles = DateTimeStyles.AssumeUniversal }
            },
        };
    }

    internal class EventUnionConverter : JsonConverter
    {
        public override bool CanConvert(Type t) => t == typeof(EventUnion) || t == typeof(EventUnion?);

        public override object ReadJson(JsonReader reader, Type t, object existingValue, JsonSerializer serializer)
        {
            switch (reader.TokenType)
            {
                case JsonToken.String:
                case JsonToken.Date:
                    var stringValue = serializer.Deserialize<string>(reader);
                    return new EventUnion { String = stringValue };
                case JsonToken.StartArray:
                    var arrayValue = serializer.Deserialize<EventClass[]>(reader);
                    return new EventUnion { EventClassArray = arrayValue };
            }
            throw new Exception("Cannot unmarshal type EventUnion");
        }

        public override void WriteJson(JsonWriter writer, object untypedValue, JsonSerializer serializer)
        {
            var value = (EventUnion)untypedValue;
            if (value.String != null)
            {
                serializer.Serialize(writer, value.String);
                return;
            }
            if (value.EventClassArray != null)
            {
                serializer.Serialize(writer, value.EventClassArray);
                return;
            }
            throw new Exception("Cannot marshal type EventUnion");
        }

        public static readonly EventUnionConverter Singleton = new EventUnionConverter();
    }
}

Thanks for your answer. Actually I tried the same thing by using an online json to c# object tool. But I got another error. Like below: Error converting value "Successful Request: 96 Results" to type 'DataMigration.EventClass'. Path '[0]', line 1, position 33.
I think I got this error because "Successful Request: 96 Results" does not have property name but only value.The thing is I cannot touch the service result since it is external.

Collectives™ on Stack Overflow

JSON deserialization error when property name is missing

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related