Deserialize JSON to Array or List with HTTPClient .ReadAsAsync using .NET 4.0 Task pattern

Question

I'm trying to deserialize the JSON returned from http://api.usa.gov/jobs/search.json?query=nursing+jobs using the .NET 4.0 Task pattern. It returns this JSON ('Load JSON data' @ http://jsonviewer.stack.hu/).

[
  {
    "id": "usajobs:353400300",
    "position_title": "Nurse",
    "organization_name": "Indian Health Service",
    "rate_interval_code": "PA",
    "minimum": 42492,
    "maximum": 61171,
    "start_date": "2013-10-01",
    "end_date": "2014-09-30",
    "locations": [
      "Gallup, NM"
    ],
    "url": "https://www.usajobs.gov/GetJob/ViewDetails/353400300"
  },
  {
    "id": "usajobs:359509200",
    "position_title": "Nurse",
    "organization_name": "Indian Health Service",
    "rate_interval_code": "PA",
    "minimum": 42913,
    "maximum": 61775,
    "start_date": "2014-01-16",
    "end_date": "2014-12-31",
    "locations": [
      "Gallup, NM"
    ],
    "url": "https://www.usajobs.gov/GetJob/ViewDetails/359509200"
  },
  ...
]

Index Action:

  public class HomeController : Controller
  {
    public ActionResult Index()
    {
      Jobs model = null;
      var client = new HttpClient();
      var task = client.GetAsync("http://api.usa.gov/jobs/search.json?query=nursing+jobs")
        .ContinueWith((taskwithresponse) =>
        {
          var response = taskwithresponse.Result;
          var jsonTask = response.Content.ReadAsAsync<Jobs>();
          jsonTask.Wait();
          model = jsonTask.Result;
        });
      task.Wait();
      ...
     }

Jobs and Job class:

  [JsonArray]
  public class Jobs { public List<Job> JSON; }

  public class Job
  {
    [JsonProperty("organization_name")]
    public string Organization { get; set; }
    [JsonProperty("position_title")]
    public string Title { get; set; }
  }

When I set a breakpoint on jsonTask.Wait(); and examine jsonTask the status is Faulted. The InnerException is "Type ProjectName.Jobs is not a collection."

I started with the Jobs type without the JsonArray attribute and Jobs as an array (Job[]) and got this error.

  public class Jobs { public Job[] JSON; }

    +       InnerException  {"Cannot deserialize the current JSON array (e.g. [1,2,3]) into type 'ProjectName.Models.Jobs' because the type requires a JSON object (e.g. {\"name\":\"value\"}) to deserialize correctly.\r\n
    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<T> 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.\r\n
Path '', line 1, position 1."}  System.Exception {Newtonsoft.Json.JsonSerializationException}

How would I process this site's JSON with the .NET 4.0 Task pattern? I would like to get this working before moving onto the await async pattern in .NET 4.5.

ANSWER UPDATE:

Here's an example using the .NET 4.5 async await pattern with brumScouse's answer.

 public async Task<ActionResult>Index()
 {
    List<Job> model = null;
    var client = newHttpClient();

    // .NET 4.5 async await pattern
    var task = await client.GetAsync(http://api.usa.gov/jobs/search.json?query=nursing+jobs);
    var jsonString = await task.Content.ReadAsStringAsync();
    model = JsonConvert.DeserializeObject<List<Job>>(jsonString);
    returnView(model);
 }

You will need to bring in the System.Threading.Tasks namespace.
Note: there is no .ReadAsString method available on .Content which is why I used the .ReadAsStringAsync method.

Answer 1

Instead of handcranking your models try using something like the Json2csharp.com website. Paste In an example JSON response, the fuller the better and then pull in the resultant generated classes. This, at least, takes away some moving parts, will get you the shape of the JSON in csharp giving the serialiser an easier time and you shouldnt have to add attributes.

Just get it working and then make amendments to your class names, to conform to your naming conventions, and add in attributes later.

EDIT: Ok after a little messing around I have successfully deserialised the result into a List of Job (I used Json2csharp.com to create the class for me)

public class Job
{
        public string id { get; set; }
        public string position_title { get; set; }
        public string organization_name { get; set; }
        public string rate_interval_code { get; set; }
        public int minimum { get; set; }
        public int maximum { get; set; }
        public string start_date { get; set; }
        public string end_date { get; set; }
        public List<string> locations { get; set; }
        public string url { get; set; }
}

And an edit to your code:

        List<Job> model = null;
        var client = new HttpClient();
        var task = client.GetAsync("http://api.usa.gov/jobs/search.json?query=nursing+jobs")
          .ContinueWith((taskwithresponse) =>
          {
              var response = taskwithresponse.Result;
              var jsonString = response.Content.ReadAsStringAsync();
              jsonString.Wait();
              model = JsonConvert.DeserializeObject<List<Job>>(jsonString.Result);

          });
        task.Wait();

This means you can get rid of your containing object. Its worth noting that this isn't a Task related issue but rather a deserialisation issue.

EDIT 2:

There is a way to take a JSON object and generate classes in Visual Studio. Simply copy the JSON of choice and then Edit> Paste Special > Paste JSON as Classes. A whole page is devoted to this here:

http://blog.codeinside.eu/2014/09/08/Visual-Studio-2013-Paste-Special-JSON-And-Xml/

Answer 2

var response = taskwithresponse.Result;
          var jsonString = response.ReadAsAsync<List<Job>>().Result;

Answer 3

The return type depends on the server, sometimes the response is indeed a JSON array but sent as text/plain

Setting the accept headers in the request should get the correct type:

client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json")); 

which can then be serialized to a JSON list or array. Thanks for the comment from @svick which made me curious that it should work.

The Exception I got without configuring the accept headers was System.Net.Http.UnsupportedMediaTypeException.

Following code is cleaner and should work (untested, but works in my case):

    var client = new HttpClient();
    client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
    var response = await client.GetAsync("http://api.usa.gov/jobs/search.json?query=nursing+jobs");
    var model = await response.Content.ReadAsAsync<List<Job>>();