Cannot Deserialize JSON Object

Question

My problem is that I'm getting this error

"Cannot deserialize the current JSON object (e.g. {\"name\":\"value\"}) into type 'System.Collections.Generic.List`1[api.Controllers.Journey]' because the type requires a JSON array (e.g. [1,2,3]) to deserialize correctly" ... When I try to serialize my API json response.

The API return something like this:

{
"Transport": [
    {
        "$id": "6",
        "SourceID": "1",
        "Context": "1",
        "Id": "AMADEUS#1",
        "Provider": null,
        "Journey": {
            "SourceID": "R1G0S0",
            "Duration": "42000",
            "Id": "5b6db9c6bfac4"
        }

    },
    {
        "$id": "7",
        "SourceID": "1",
        "Context": "1",
        "Id": "AMADEUS#1",
        "Provider": null,
        "Journey": [
            {
                "SourceID": "R1G0S0",
                "Duration": "42000",
                "Id": "5b6db9c6bfac4"
            },
            {
                "SourceID": "R1G0S1",
                "Duration": "42000",
                "Id": "5b6db9c6bsac4"
            }
        ]

    }
]
}

The Journey field is an JObject at first result, but is an JArray on second...

And I'm getting the error when I deserialize:

Transport Transport = JsonConvert.DeserializeObject<Transport>(json_response);

My class properties:

public class Transport{
    public string SourceID { get; set; }
    public string Context { get; set; }
    public string Id { get; set; }
    public ProviderOD Provider { get; set; }
    public Journey[] Journey { get; set; }
    public PriceOD Price { get; set; }
}
public class Journey
{
    public string Id { get; set; }
    public string SourceID { get; set; }
    public string Duration { get; set; }
}

What should I do, to set Journey[ ] or Journey dynamically ??

Thanks in advance ...

score 2 · Answer 1 · answered Aug 10 '18 at 16:43

2

Your class declaration is not right, you have to use the following to decode

TransportRootObject Transport = JsonConvert.DeserializeObject<TransportRootObject>(json_response);

and this class(es) declaration

public class TransportRootObject
{
    public List<Transport> Transport { get; set; }
}
public class Transport
{
    [JsonProperty("$id")]
    public string Id { get; set; }
    public string SourceID { get; set; }
    public string Context { get; set; }
    public string Id { get; set; }
    public ProviderOD Provider { get; set; }
    public List<Journey> Journey { get; set; }
}
public class Journey
{
    public string Id { get; set; }
    public string SourceID { get; set; }
    public string Duration { get; set; }
}

answered Aug 10 '18 at 16:43

cramopy

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You're right, thanks, but I'm still getting the error... The real problem is when serialize the first journey is not a List. So thats why is giving me this "Cannot deserialize the current JSON object (e.g. {\"name\":\"value\"}) into type 'System.Collections.Generic.List`1[api.Controllers.Journey]' because the type requires a JSON array (e.g. [1,2,3]) to deserialize correctly" – Aly Daniel Zuniaga Ramos Aug 10 '18 at 16:47
@AlyDanielZuniagaRamos the problem here is, that JSON does not allow a *comma* after the last element. Thus `"Id": "5b6db9c6bfac4", }` has to get rid of the last *comma* before the `}` to become valid. This has to be done at all instances of `, }`. – cramopy Aug 10 '18 at 16:52
No man, that was my error typing here... but not solved my problem... Thanks – Aly Daniel Zuniaga Ramos Aug 10 '18 at 16:59
@AlyDanielZuniagaRamos Okay, then there is another problem. please see https://stackoverflow.com/questions/44100383/handling-json-single-object-and-array Your JSON is not static within its structure. Please see the provided link and feel free to upvote and mark my answer as correct. – cramopy Aug 10 '18 at 17:04

score 0 · Answer 2 · answered Aug 10 '18 at 16:43

So there's a few issues here. Your top level Transport object in your JSON is actually an array of transport objects. So you need an extra class:

public class DocumentRoot
{
    public List<Transport> Transport { get; set; }
}

Then you want:

var DocumentRoot = JsonConvert.DeserializeObject<DocumentRoot>(json_response);
//DocumentRoot.Transport is now a List<Transport> of your transport elements from the document.

In your JSON one of the member names is "$id" which of course isn't valid in C#, so to make this behave you need to add a [JsonProperty(PropertyName = "$id")] attribute on your Id property to tell the serializer the name.

You're right, thanks, but I'm still getting the error... The real problem is when serialize the first journey is not a List. So thats why is giving me this "Cannot deserialize the current JSON object (e.g. {\"name\":\"value\"}) into type 'System.Collections.Generic.List`1[api.Controllers.Journey]' because the type requires a JSON array (e.g. [1,2,3]) to deserialize correctly" — Aly Daniel Zuniaga Ramos, Aug 10 '18 at 16:47

score 0 · Accepted Answer · answered Aug 10 '18 at 17:07

I think your issue is that you've got poorly formatted JSON being returned from your API. If Journey is an array, it should always return as an array/list...not an object if there is only 1 and then an array if there is more than one.

If this is a third party API that you are unable to fix then your next option is to use a custom converter to handle weirdly formatted json like this.

I don't recall where i found the original source/solution for this but I'll walk you through the steps.

First you'll need to create a new class such as this.

public class SingleOrArrayConverter<T> : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return (objectType == typeof(List<T>));
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        JToken token = JToken.Load(reader);
        if (token.Type == JTokenType.Array)
        {
            return token.ToObject<List<T>>();
        }
        return new List<T> { token.ToObject<T>() };
    }

    public override bool CanWrite
    {
        get { return false; }
    }

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

This is your custom converter to handle a "sometimes array, sometimes object" situation. It pretty much just does a test to determine if its an array or an object and handles accordingly.

Then, within your transport class, you'll add the attribute above the Journey array property like so.

[JsonConverter(typeof(SingleOrArrayConverter<Journey>))]
public List<Journey> Journey { get; set; }

This should then handle situations where journey comes through as an array or as an object.

Cannot Deserialize JSON Object

3 Answers3