Error when deserializing JSON to Object

Question

I need to convert JSON data that I get from a REST API and convert them to CSV for some analytic. The problem is that the JSON data do not necessarily follow the same content, so I can't define a type for mapping. This has become a challenge that is taking too much of my time. I have already created some code, but of course it is not working as it throws exception on this line

var data = JsonConvert.DeserializeObject<List<object>>(jsonData);

The error is:

Additional information: Cannot deserialize the current JSON object (e.g. {"name":"value"}) into type 'System.Collections.Generic.List`1[System.Object]' because the type requires a JSON array (e.g. [1,2,3]) to deserialize correctly.

To fix this error either change the JSON to a JSON array (e.g. [1,2,3]) or change the deserialized type so that it is a normal .NET type (e.g. not a primitive type like integer, not a collection type like an array or List) that can be deserialized from a JSON object. JsonObjectAttribute can also be added to the type to force it to deserialize from a JSON object.

Path 'data', line 2, position 10.

please let me know what I can do to get this going.

A sample of data would be like this, the fields of data can change very often, for example a new field can be added the next day, so I don't have the liberty to create a .Net class to map the data.

{
  "data": [
    {
      "ID": "5367ab140026875f70677ab277501bfa",
      "name": "Happiness Initiatives - Flow of Communication/Process & Efficiency",
      "objCode": "PROJ",
      "percentComplete": 100.0,
      "plannedCompletionDate": "2014-08-22T17:00:00:000-0400",
      "plannedStartDate": "2014-05-05T09:00:00:000-0400",
      "priority": 1,
      "projectedCompletionDate": "2014-12-05T08:10:21:555-0500",
      "status": "CPL"
    },
    {
      "ID": "555f452900c8b845238716dd033cf71b",
      "name": "UX Personalization Think Tank and Product Strategy",
      "objCode": "PROJ",
      "percentComplete": 0.0,
      "plannedCompletionDate": "2015-12-01T09:00:00:000-0500",
      "plannedStartDate": "2015-05-22T09:00:00:000-0400",
      "priority": 1,
      "projectedCompletionDate": "2016-01-04T09:00:00:000-0500",
      "status": "APR"
    },
    {
      "ID": "528b92020051ab208aef09a4740b1fe9",
      "name": "SCL Health System - full Sitecore implementation (Task groups with SOW totals in Planned hours - do not bill time here)",
      "objCode": "PROJ",
      "percentComplete": 100.0,
      "plannedCompletionDate": "2016-04-08T17:00:00:000-0400",
      "plannedStartDate": "2013-11-04T09:00:00:000-0500",
      "priority": 1,
      "projectedCompletionDate": "2013-12-12T22:30:00:000-0500",
      "status": "CPL"
    }
 ]
}



namespace BusinessLogic
{
    public class JsonToCsv
    {

       public string ToCsv(string jsonData, string datasetName)
       {
          var data = JsonConvert.DeserializeObject<List<object>>(jsonData);
          DataTable table = ToDataTable(data); 
          StringBuilder result = new StringBuilder();

            for (int i = 0; i < table.Columns.Count; i++)
            {
                result.Append(table.Columns[i].ColumnName);
                result.Append(i == table.Columns.Count - 1 ? "\n" : ",");
            }

            foreach (DataRow row in table.Rows)
            {
                for (int i = 0; i < table.Columns.Count; i++)
                {
                    result.Append(row[i].ToString());
                    result.Append(i == table.Columns.Count - 1 ? "\n" : ",");
                }
            }

            return result.ToString().TrimEnd(new char[] {'\r', '\n'});

        }

        private DataTable ToDataTable<T>( IList<T> data )
            {
            PropertyDescriptorCollection props = TypeDescriptor.GetProperties(typeof(T));
            DataTable table = new DataTable();
            for (int i = 0 ; i < props.Count ; i++)
                {
                PropertyDescriptor prop = props[i];
                table.Columns.Add(prop.Name, prop.PropertyType);
                }

            object[] values = new object[props.Count];
            foreach (T item in data)
                {
                for (int i = 0 ; i < values.Length ; i++)
                    {
                    values[i] = props[i].GetValue(item);
                    }

                table.Rows.Add(values);
                }

            return table;
            }


        }
}

The example JSON you posted does not correlate to a single object in your error instead of the array you're trying to cast it to. — krillgar, Dec 18 '15 at 20:16

score 11 · Accepted Answer · answered Dec 19 '15 at 19:12

The real issue here is that you are trying to deserialize into a List<object> but your JSON actually represents a single object containing a data property which then contains a list of objects. That is why you are getting this error. Json.Net can't deserialize a single object into a list. I think what you really want to do is define a container class like this:

class Root
{
    public List<Dictionary<string, object>> Data { get; set;}
}

Then deserialize like this:

var data = JsonConvert.DeserializeObject<Root>(jsonData).Data;

You will then end up with a list of dictionaries, where each dictionary represents one item in the JSON array. The dictionary key-value pairs are the dynamic values in each item. You can then work with these as you would with any other dictionary. For example, here is how you would dump out all the data:

foreach (var dict in data)
{
    foreach (var kvp in dict)
    {
        Console.WriteLine(kvp.Key + ": " + kvp.Value);
    }
    Console.WriteLine();
}

Fiddle: https://dotnetfiddle.net/6UaKhJ

your answer is the most simplest and easiest one to implement. It solved my problem. thanks — Payam, Dec 21 '15 at 20:58
Thank you! its working great..for json in container class Root { public List> Data { get; set;} } — charulatha krishnamoorthy, Dec 13 '19 at 09:55

score 1 · Answer 2 · edited May 23 '17 at 12:23

What you're looking for is the dynamic type. Though unrelated, this answer contains much of the information on how you'll be able to iterate through the changing properties on your object.

You will need to add some additional work to figure out how to handle your result when it is an array versus a single object as your error shows us. However, this is a good first step for you.

Basically, a dynamic object is a Dictionary, much like how a JSON object is treated in JavaScript. You just need to iterate through each of the KeyValuePair objects within the main object and go through their properties.

var data = JsonConvert.DeserializeObject<dynamic>(jsonData);
var rows = new List<string>();

// Go through the overall object, and get each item in 
// the array, or property in a single object.
foreach (KeyValuePair<string, object> item in data)
{
    dynamic obj = item.Value;
    var row = "";

    // Perhaps add a check here to see if there are more
    // properties (if it is an item in an array). If not
    // then you are working with a single object, and each
    // item is a property itself.
    foreach (KeyValuePair<string, object> prop in obj)
    {
        // Very dummy way to demo adding to a CSV
        string += prop.Value.ToString() + ",";
    }

    rows.Add(string);
}

This is far from a complete example, but we don't have enough information to go on to help you finish what you're trying to do.

score 1 · Answer 3 · edited May 09 '20 at 09:00

1

You are trying to deserialize into a List but your JSON actually represents a single object containing a data property containing list of objects. That is why you are getting this error. Json.Net can't deserialize a single object into a list.

Please try this:Create a class which contain single property on datatype Object and pass this class for deserialization.

class Parent
{
    public object Data { get; set;}
}

Then deserialize like this:

var output = JsonConvert.DeserializeObject<Parent>(jsonData);

edited May 09 '20 at 09:00

rizerphe

1,340
1
14
24

answered May 09 '20 at 06:06

Somen

11
1

Please properly format code, [click here to learn how](https://stackoverflow.com/help/formatting). – rizerphe May 09 '20 at 06:29

Jared · Answer 4 · 2015-12-18T20:17:36.763

0

Try using this class instead of Object

public class Datum
{
    public string ID { get; set; }
    public string name { get; set; }
    public string objCode { get; set; }
    public double percentComplete { get; set; }
    public string plannedCompletionDate { get; set; }
    public string plannedStartDate { get; set; }
    public int priority { get; set; }
    public string projectedCompletionDate { get; set; }
    public string status { get; set; }
}

public class RootObject
{
    public List<Datum> data { get; set; }
}

Change to this:

var data = JsonConvert.DeserializeObject<RootObject>(jsonData);

edited Dec 18 '15 at 20:17

answered Dec 18 '15 at 20:12

Jared

310
1
9

The problem is that I can't do this. This data can change tomorrow. The next day I will get username added to it too or other fields. It is very dynamic. Your suggestion works for this particular case, but what if it changes very regularly. I can't go everyday and update the class. – Payam Dec 18 '15 at 20:22
2

I see. Ok. What about using List ? – Jared Dec 18 '15 at 20:41
In my case I have an integration engine. The number of classes to manage and the number of fields is too massive and since we are using a document database we prefer to not have to map all fields. It should always pass all data as json regardless of what new data it contains. So what do you do in this case? – Urasquirrel Apr 13 '21 at 15:44

score 0 · Answer 5 · answered Dec 18 '15 at 20:36

0

If your data is dynamic so try a dynamic list:

using System.Web.Script.Serialization;

JavaScriptSerializer jss = new JavaScriptSerializer();
var d=jss.Deserialize<dynamic>(str);

answered Dec 18 '15 at 20:36

Rodolfo

247
2
14

this is not a question for javascript. This question is .net C#. Completely different language. – Urasquirrel Apr 13 '21 at 15:45

joordan831 · Answer 6 · 2015-12-18T21:35:47.780

Since you're trying to deserialize an object type into a list type, it won't deseralize directly.

You can do this:

var data = JsonConvert.DeserializeObject<ObjectDataList>(jsonData);
var rows = new List<DeserializedData>();

foreach (dynamic item in data)
{
    var newData = new DeserializedData();
    foreach (dynamic prop in item)
    {
         var row = new KeyValuePair<string, string>
         (prop.Name.ToString(), prop.Value.ToString());
         newData.Add(row);
    }
    rows.Add(newData);
}

Here are new classes

//class for key value type data

class DeserializedData
{
    List<KeyValuePair<string, string>> NewData = 
    new List<KeyValuePair<string, string>>();

    internal void Add(KeyValuePair<string, string> row)
    {
        NewData.Add(row);
    }
}


[DataContract]
class ObjectDataList
{
    [DataMember(Name ="data")]
    List<object> Data { get; set; }
    public IEnumerator<object> GetEnumerator()
    {
        foreach (var d in Data)
        {
            yield return d;
        }
    }
}

score 0 · Answer 7 · answered May 30 '18 at 12:06

As far as I can tell, more recent versions of Newtonsoft can actually do this now, no additional work required.

I was working with the binary version however, and this did still have the issue - I had a test where you could configure to use binary or json, and the json version worked just fine, but the binary complained about not getting an array type.

I started using the BsonDataReader for this, and was looking through the properties and methods on it to see how I could best look at the contents, and lo and behold, this had a property called:

reader.ReadRootValueAsArray

Setting this to 'true' did the trick.

score 0 · Answer 8 · answered May 06 '23 at 21:37

this worked for me
make a class for root element
public class JsonRoot{public List<Animal> Animmals { get; set; }}
and deserialize by accessing the object
List <Animal> deserializedObject = JsonConvert.DeserializeObject<JsonRoot> (jsonString).Animmals;

Error when deserializing JSON to Object

8 Answers8

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