Question 160614 in Json Question posted in
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How do you add a new object to an array in a nested JSON document?

Disclaimer: C# isn’t really my forte, guys; I’m usually a database guy. Alot of this is pieced together code I’ve found here and there; so please go easy on me.

I’m trying to figure out how to add a new object to an existing JSON document that a user opens and then saving the updates to that file. The below is a made up JSON that follows the same basic structure and I want to be able to add a new "car" to a "person". The "new" values are coming via textboxes and dropdowns.

{
  "Name": "Bob Bob",
  "City": "Louisville",
  "State": "Kentucky",
  "Address": "123 City Ln",
  "Cars": [
    {
      "Make": "Ford",
      "Model": "Explorer",
      "Color": "White"
    },
    {
      "Make": "Dodge",
      "Model": "Caravan",
      "Color": "White"
    },
    {
      "Make": "Bat",
      "Model": "Mobile",
      "Color": "Black:"
    }
  ],
  "Jobs": [
    {
      "Employer": "Walmart",
      "Position": "Greeter",
      "Pay": "$35,000",
      "EndDate": "12/25/1999"
    },
    {
      "Employer": "Target",
      "Position": "Cashier",
      "Pay": "$32,000",
      "EndDate": "1/1/2002"
    },
    {
      "Employer": "SkyNet",
      "Position": "Programmer",
      "Pay": "$86,000",
      "EndDate": "5/8/2023"
    }
  ]
}

I have the below classes set up

public class Person
{
    public string Name { get; set;}
    public string City { get; set;}
    public string State { get; set;}
    public string Address { get; set;}
    public Cars[] Cars {get; set;}
    public Jobs[] Jobs {get; set;}
}

public class Cars
{
    public string Make { get; set;}
    public string Model { get; set;}
    public string Color { get; set;}
}

public class Jobs
{
    public string Employer { get; set;}
    public string Position { get; set;}
    public string Pay { get; set;}
    public string EndDate { get; set;}
}

Here’s the code I have so far

private void btnSaveUpdates_Click(object sender, EventArgs e)
{
    string Make = cbMake.Text;
    string Model = txtModel.Text;
    string Color = cbColor.Text;
    string filePath = txtFileLoc.Text;

    DoJSONWork(filePath, Make, Model, Color);
}

public static void DoJSONWork(string filePath, string Make, string Model, string Color)
{
    var FileStream = File.OpenRead(filePath);

    using (StreamReader reader = new StreamReader(FileStream))
    {
        using (JsonTextReader JSONreader = new JsonTextReader(reader))
            {
                JSONreader.SupportMultipleContent = true;

                var serializer = new JsonSerializer();
                while (JSONreader.Read())
                {
                    if (JSONreader.TokenType == JsonToken.StartObject)
                    {
                        Person p = serializer.Deserialize<Person>(JSONreader);

                        Cars cars = p.Cars.FirstOrDefault(c => c.Make + c.Model + c.Color == Make + Model + Color);
                        if (cars == null)
                        {
                            cars = new Cars
                            {
                                Make = Make,
                                Model = Model,
                                Color = Color
                            };
                            p.Cars = p.Cars.Concat(new Cars[]
                            {
                              cars
                            }).ToArray();

                        }

                    }
                }
            }
        }

        //I honestly don't know what to do next 
    }

I’m struggling to figure out how to update the "cars" in the JSON document. Do I need to deserialize and serialize the entire JSON doc?

Tags:

2

Answers


  1. 0

    the short answer is Yes.
    in order to manipulate a json first you should Deserialize it to a Collection of a type that c# understands after you can add data to the collection and then serialize it again the code goes something like this

    var list = JsonConvert.DeserializeObject<List<Person>>(myJsonString);

    then you can find or add an object to the list

    list.Add(new Person());

    and in the end, you must convert your list to json

    var convertedToJson = JsonConvert.SerializeObject(list);

    by the way JsonConvert is in the namespace of using Newtonsoft.Json;
    there are plenty of ways to convert.
    this package is one of the easy ones

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  2. 0

    you don’t need any classes, just parse your json

        var json =File.ReadAllText(filePath);

    var jObj = JObject.Parse(json);
    var cars = (JArray)jObj["Cars"];
    
    if (cars == null) cars = new JArray();
    else if (cars.Any(c => ((string)c["Make"]) == Make
                                && ((string)c["Model"]) == Model
                                 && ((string)c["Color"]) == Color)) 
                                return;
    cars.Add(new JObject
    {

        ["Make"] = Make,
        ["Model"] = Model,
        ["Color"] = Color
    });
    
    json=jObj.ToString();
    
    File.WriteAllText(filePath, json);

    or you can use Cars class, since you have it already

        var jObj = JObject.Parse(json);

    List<Cars> cars = jObj["Cars"].ToObject<List<Cars>>();

    if (cars.Any(c => c.Make + c.Model + c.Color == Make + Model + Color)) return;

    cars.Add(new Cars
    {
        Make = Make,
        Model = Model,
        Color = Color
    });

    jObj["Cars"] = JArray.FromObject(cars);

    json = jObj.ToString();
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