JSON.Net Serialize Collection To Array of Arrays

Question

By default DataTables Ajax expects JSON data to be an array of arrays.

Using JSON.Net is it possible to serialize a collection into an array of arrays instead of an array of objects via an attribute/setting or does it have to be done via a custom JsonConverter. The object I am trying to serialize is as follows:

public class DeviceIndex
{
    public int Id { get; set; }

    [Display(Name = "Asset Tag")]
    public string AssetTag { get; set; }

    [Display(Name = "Lease End")]
    [DataType(DataType.Date)]
    public DateTime LeaseEndDate { get; set; }

    public string Type { get; set; }

    [Display(Name = "Operating System")]
    public string OperatingSystem { get; set; }

    public string Model { get; set; }
}

And my controller action is as follows:

public IActionResult IndexJson()
{
    var model = _db.Devices.Select(d => new DeviceIndex { ... }).ToList();
    return Content(JsonConvert.SerializeObject(new { data = model }), "application/json");
}

Which outputs the JSON:

{
  "data": [
    {
      "Id": 1649,
      ...
    },
    {
      "Id": 703,
      ...
    }
  ]
}

Though my desired results are as follows:

{
  "data": [
    [
      "1649",
      ...
    ],
    [
      "703",
      ...
    ]
  ]
}

I thought I could use the JsonArray attribute for my collection but it doesn't look to change the output.

[JsonArray]
public class DevicesIndex: IEnumerable<DeviceIndex>
{
    List<DeviceIndex> devices;

    public IEnumerator<DeviceIndex> GetEnumerator()
    {
        return devices.GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}

So you need json look like your first json, an array of array object? If yes you have to serialize List> this will be json as an array of array string. — M. Wiśnicki, Nov 23 '16 at 16:20
Looks similar to, or a duplicate of, [C# JSON.NET - Deserialize response that uses an unusual data structure](https://stackoverflow.com/questions/39461518). — dbc, Nov 24 '16 at 07:25

M. Wiśnicki · Answer 1 · 2016-11-23T17:41:11.227

You can simple way achieve it, just update your IndexJson() method using this simple sample.

You need serialize List<List<object>>, try this sample. This is List of List<string>.

public IActionResult IndexJson()
    {
        List<List<string>> data = new List<List<string>>();

        data.Add(new List<string>(new string[] {"test1", "test2"}));
        data.Add(new List<string>(new string[] {"test3", "test4"}));

        var json = JsonConvert.SerializeObject(new {data = data});
        return Content(json, "application/json");
    }

You will get this JSON

{
  "data":[
    ["test1","test2"],
    ["test3","test4"]
]}

Using Your data model

   List<List<string>> data =new List<List<string>>();

        List<DeviceIndex> deviceIndex = new List<DeviceIndex>();
        DeviceIndex item = new DeviceIndex();
        item.Id = 111;
        item.AssetTag = "Tag";
        item.LeaseEndDate = DateTime.Now;
        item.Type = "Type";
        item.OperatingSystem = "OS";
        item.Model = "Model";

        deviceIndex.Add(item);
        deviceIndex.Add(item);

        foreach (var device in deviceIndex)
        {

            data.Add(new List<string>(new string[] { device.Id.ToString(), device.AssetTag, device.AssetTag, device.OperatingSystem }));
        }

       var json =  JsonConvert.SerializeObject(new {data= data });

JSON

{
 "data":[
   ["111","Tag","Tag","OS"],
   ["111","Tag","Tag","OS"]
  ]
}

Your first example gives the desired output but the second one using a class does not. The property names should not be output and all values should be within an array, not an object within an array. — mheptinstall, Nov 23 '16 at 17:15

score 1 · Accepted Answer · edited May 08 '17 at 09:25

It looks like a custom JsonConverter is the suggested method

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

    public override object ReadJson(JsonReader reader, 
                                    Type objectType, 
                                    object existingValue, 
                                    JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }

    public override void WriteJson(JsonWriter writer, 
                                   object value, 
                                   JsonSerializer serializer)
    {
        if (value == null) return;

        writer.WriteStartArray();

        var properties = value.GetType().GetProperties();
        foreach (var property in properties)
            writer.WriteValue(value.GetType().GetProperty(property.Name).GetValue(value));

        writer.WriteEndArray();
    }
}

JSON.Net Serialize Collection To Array of Arrays

2 Answers2