Cannot deserialize the current JSON array after API call

Question

I have a NET Core MVC web application where I'm calling an API to show the results in my UI. I'm calling the API using an ajax call but after calling the API I get the following error message:

An unhandled exception occurred while processing the request. JsonSerializationException: Cannot deserialize the current JSON array (e.g. [1,2,3]) into type 'ProjectName.Models.ControllerName' because the type requires a JSON object (e.g. {"name":"value"}) to deserialize correctly.

JSON Result from API:

[
    [
        {
            "Col1": "Value",
            "Col2": "Value",
            "Col3": "Value",
            "Col4": [
                {
                    "Value": [
                        {}
                    ]
                },
                {
                    "Value": [
                        {}
                    ]
                }
            ],
            "Col5": "Value"
        }
    ],
    [
        {
            "Col1": "Value",
            "Col2": "Value",
            "Col3": "Value",
            "Col5": "Value"
         }
     ],
     [
        {
            "Col1": "Value",
            "Col2": "Value",
            "Col3": "Value",
            "Col4": [
                {
                    "Value": [
                        {}
                    ]
                },
                {
                    "Value": [
                        {}
                    ]
                 }
             ],
             "Col5": "Value"
        }
    ]
]

MyController

[HttpGet, ActionName("GetData")]
public async Task<IActionResult> GetReport()
{
    return this.Json(await _cuRepo.GetReportAsync("https://apiurlforcall/report"));
}

Repository

public async Task<IEnumerable<T>> GetReportAsync(string url)
{
    using (var client = new HttpClient())
    {
        client.DefaultRequestHeaders.Add("Token", "apiToken");
        HttpResponseMessage response = await client.GetAsync(url);
        if (response.StatusCode == System.Net.HttpStatusCode.OK)
        {
            //jsonString is populated with the above JSON result
            var jsonString = await response.Content.ReadAsStringAsync();
            return JsonConvert.DeserializeObject<IEnumerable<T>>(jsonString);
        }
        else
            return null;
    }
}

AjaxCall (What I'm trying to do)

$.ajax({
    url: "Controller/GetData",
    data: {},
    method: "GET",
    success: function (data) {
        var json = data;
        var html = "";

        for (var x = 0; x < json.length; x++) {
            html += "<tr><td>" + json[x].Col1+ "</td><td>" + json[x].Col2+ "</td></tr>";
        }
        $('#MyTable').html("");
        $('#MyTable').html(html);
        console.log(json);
    }
});

To be honest, I don't have too much experience with net core, I'm trying to learn by doing this project but this issue is a big roadblock and I'm kind of lost.

Can you please add your class that you are using to deserialize and also the api response? — Manprit Singh Sahota
– Manprit Singh Sahota, Commented Jan 11, 2021 at 5:55
@ManpritSinghSahota Hello, I added the api response and what I'm using to deserialize is this IEnumerable<T> — User1899289003
– User1899289003, Commented Jan 11, 2021 at 6:06
Sometimes your Col4 in json is a list,and sometimes it is a string.Col4 cannot be like this. — Yiyi You
– Yiyi You, Commented Jan 11, 2021 at 6:08
@YiyiYou Sorry, my fault, Col4 always is a list, sometimes is returned by the API and sometimes not as the above example — User1899289003
– User1899289003, Commented Jan 11, 2021 at 6:12

Yiyi You · Accepted Answer · 2021-01-11 07:22:19Z

2

You can do like this:

models:

public class Cols
    {
        public string  Col1 { get; set; }
        public string Col2 { get; set; }
        public string Col3 { get; set; }
        public List<Col4> Col4 { get; set; }
        public string Col5 { get; set; }

        
    }
    public class Col4
    {
        public List<Col> Value { get; set; }
    }
    public class Col
    { 

    }

change

return JsonConvert.DeserializeObject<IEnumerable<T>>(jsonString);

to

return JsonConvert.DeserializeObject<List<List<Cols>>>(jsonString);

Update:

1.change

public async Task<IEnumerable<T>> GetReportAsync(string url)

to

public async Task<List<List<Cols>>> GetReportAsync(string url)

2.change

var json = data;

to

var json = data[0];

3.change

html += "<tr><td>" + json[x].Col1+ "</td><td>" + json[x].Col2+ "</td></tr>";

to

html += "<tr><td>" + json[x].col1+ "</td><td>" + json[x].col2+ "</td></tr>";

edited Jan 11, 2021 at 7:22

answered Jan 11, 2021 at 6:23

Yiyi You

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3 Comments

User1899289003 Over a year ago

Doing this I'm getting "cannot implicitly convert System.Generics.List to System.Generics.IEnumerable<T>"

User1899289003 Over a year ago

I do this to avoid the error return (IEnumerable<T>)JsonConvert.DeserializeObject<List<List<Cols>>>(jsonString); but now I'm getting this error: InvalidCastException: Unable to cast object of type 'System.Collections.Generic.List1[System.Collections.Generic.List1[ProjectName.Models.Cols]]' to type 'System.Collections.Generic.IEnumerable`1[ProjectName.Models.Cols]'

Yiyi You Over a year ago

I have updated my answer.You need to return Task<List<List<Cols>>>

Manprit Singh Sahota · Accepted Answer · 2021-01-11 07:00:48Z

1

You can use below class to deserialize your json:

public class DataObject
    {
        public ColDetails[][] MyData { get; set; }
    }

    public class ColDetails
    {
        public string Col1 { get; set; }
        public string Col2 { get; set; }
        public string Col3 { get; set; }
        public Col4[] Col4 { get; set; }
        public string Col5 { get; set; }
    }

    public class Col4
    {
        public Value[] Value { get; set; }
    }

    public class Value
    {
    }

Then, return the object that you want after converting to your class.

Use below code to deserialize:

JsonConvert.DeserializeObject<DataObject>(jsonString);

answered Jan 11, 2021 at 7:00

Manprit Singh Sahota

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