C# Parsing JSON Issue

Question

I have following JSON and I am using Json.NET (Newtonsoft.Json):

{
  "total_items": "62",
  "page_number": "6",
  "page_size": "10",
  "page_count": "7",
  "cars": {
    "car": [     
      {
        "car_name": "Honda", 
        "engines": {
          "engine": [  <-- HONDA has multiple engines, so this is an array
            {
              "name": "1.2L"
            },
            {
              "name": "1.8L"
            }
          ]
        },
        "country": "Japan"
        "image": {
            "thumb": {
                "url": "http://image_path/Honda.jpg" <-- Image provided
            }
        }
      },
      {
        "car_name": "Ford",
        "engines": {
          "engine": {   <-- FORD has single engine, so this is an object
              "name": "2.2L"
          }
        },
        "country": "Japan"
        "image": null  <-- image is null
      },
      { 
        "car_name": "VW",
        "engines": null,  <-- VW has no engines, so this is null
        "country": "Germany"  
        "image": null    <-- image is null
      }
    ]
  }
}

And I have following Car object:

class Car
{
    public Car() { }

    public string Name { get; set; }
    public string Country { get; set; }
    public List<String> EngineNames { get; set; }
}

I need to handle all 3 cases above (array for HONDA, object for FORD, null for VW). If it is not null, then get all engine names. So, for example above, my EngineNames list for the 3 cars would be:

Honda.EngineNames = {"1.2L", "1.8L"} // array in JSON
Ford.EngineNames = {"2.2L"} //object in JSON
VW.EngineNames = null //null in JSON

I need to parse the JSON above to get car data. I am parsing car_name and country but I don't know how to parse all engine names by handling the 3 situations above.

private Cars GetCars(string json)
{
    dynamic data = (JObject)JsonConvert.DeserializeObject(json);

    foreach (dynamic d in data.cars.car)
    {
        Car c = new Car(); 

        c.Name = (string)d.SelectToken("car_name");
        c.Country = (string)d.SelectToken("country");

        // PROBLEM: This works fine for array or null in JSON above (HONDA and VW), but it errors on JSON object (in case of FORD)
        // When handling FORD, I get error "'Newtonsoft.Json.Linq.JProperty' does not contain a definition for 'name'"
        c.EngineNames = (d.engines != null ? ((IEnumerable)d.engines.engine).Cast<dynamic>().Select(e => (string)e.name) : null);

        CarList.Add(c);
    }
    return CarList;
}

Answer 1

You should be able to use this as your class structure;

public class Rootobject
{
    public string total_items { get; set; }
    public string page_number { get; set; }
    public string page_size { get; set; }
    public string page_count { get; set; }
    public Cars cars { get; set; }
}

public class Cars
{
    public Car[] car { get; set; }
}

public class Car
{
    public string car_name { get; set; }
    public Engines engines { get; set; }
    public string country { get; set; }
}

public class Engines
{
    public object engine { get; set; }
}

//I created below class manually
public class Engine
{
    public string name { get; set; }
}

I used inbuilt functionality of VS to generate this. Steps;

1. Open a new cs file.
2. Copy your json
3. Go to Edit menu> Paste special
4. Select Paste JSON as classes

Once this is done, it should be just a matter of creating two methods to serialize and deserialize.

Updated with serialise/deserialise methods

        private static T Deserialise<T>(string json)
        {
            var myopject = JsonConvert.DeserializeObject<T>(json);
            return myopject;
        }

        private static string Serialise<T>(T value)
        {
            var mycontent =  JsonConvert.SerializeObject(value);
            return mycontent;
        }

Now to test above methods, you can do this.

            var jsonstring = @"{
              ""total_items"": ""62"",
              ""page_number"": ""6"",
              ""page_size"": ""10"",
              ""page_count"": ""7"",
              ""cars"": {
                ""car"": [
                  {
                    ""car_name"": ""Honda"",
                    ""engines"": {
                      ""engine"": [
                        {
                          ""name"": ""1.2L""
                        },
                        {
                          ""name"": ""1.8L""
                        }
                      ]
                    },
                    ""country"": ""Japan""
                  },
                  {
                    ""car_name"": ""Ford"",
                    ""engines"": {
                      ""engine"": {
                        ""name"": ""2.2L""
                      }
                    },
                    ""country"": ""Japan""
                  },
                  {
                    ""car_name"": ""VW"",
                    ""engines"": null,
                    ""country"": ""Germany""
                  }
                ]
              }
            }";
            var myobject = Deserialise<Rootobject>(jsonstring);

            //if you want to parse engines you can do something like    this.

          if (myobject.cars != null && myobject.cars.car != null && myobject.cars.car.Any())
        {
            foreach (Car car in myobject.cars.car)
            {
                if (car.engines != null && car.engines.engine != null)
                {
                    bool isList = false;
                    try
                    {
                        var eng = Deserialise<Engine>(car.engines.engine.ToString());
                    }
                    catch
                    {
                        isList = true;
                    }
                    if (isList)
                    {
                        try
                        {
                            var eng = Deserialise<List<Engine>>(car.engines.engine.ToString());
                        }
                        catch
                        {
                            Debug.WriteLine("Not a list");
                        }
                    }
                }
            }
        }

            var myjson = Serialise(myobject);

Answer 2

Using the converter from here (originally a proposed duplicate, but this question had some other issues with the JSON)

Your class structure needs to be modified a bit.

Looking at this JSON:

"cars": { <-- cars is an object, not an array
    "car": [ <-- the cars object actually contains the array
      {
        "car_name": "Honda", 
        "engines": { <-- same goes for this
          "engine": [
            {

Therefore, you'll need to write wrapper classes to properly reflect the JSON. Here's what I've come up with:

public class Root 
{
    public CarHolder Cars {get;set;}
}
public class CarHolder
{
    public IList<Car> Car { get; set; }
}
public class Car
{
    public Car() { }

    public string car_name { get; set; }
    public string Country { get; set; }

    public EngineHolder Engines { get; set; }
}
public class EngineHolder 
{
    [JsonConverter(typeof(SingleOrArrayConverter<Engine>))]
    public List<Engine> Engine { get; set; }
}
public class Engine
{
    public string Name { get; set; }
}

And using the convert from the above question:

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();
    }
}

Usage:

var result = JsonConvert.DeserializeObject<Root>(jsonStr);
Console.WriteLine(result.Cars.Car[0].Engines.Engine[0].Name == "1.2L");
Console.WriteLine(result.Cars.Car[0].Engines.Engine[1].Name == "1.8L");
Console.WriteLine(result.Cars.Car[1].Engines.Engine[0].Name == "2.2L");
Console.WriteLine(result.Cars.Car[2].Engines == null);

All print true

Looping through the cars & engines

foreach(var car in result.Cars.Car)
{
    if (car.Engines != null)
    {
        foreach(var engine in car.Engines.Engine)
        {
            var engineName = engine.Name;
        }
    }
}