How to update JArray values with C# and Json.NET

Question

I'm getting an array of items from Web API (lines before this are omitted):

var cars = JArray.Parse(response.Content.ReadAsStringAsync().Result)

Inside the cars JArray it looks like this:

"cars": [{
            "id": 1,
            "make": "Audi",
            "color": "red"
        }, {
            "id": 2,
            "make": "Mercedes",
            "color": "red"
        }, {
            "id": 3,
            "make": "Ford",
            "color": "yellow"
        }]

I would like to update the color of Ford to red if Audi is also red.

How can I do that with C# and Json.NET?

You can use json path along with json token

Darshani Jayasekara
– Darshani Jayasekara

2021-07-01 13:34:47 +00:00
Commented Jul 1, 2021 at 13:34 — Darshani Jayasekara
– Darshani Jayasekara, Commented Jul 1, 2021 at 13:34
eeek dont do .Result on an async. Recipe for disaster.

Jamiec
– Jamiec

2021-07-01 14:32:12 +00:00
Commented Jul 1, 2021 at 14:32 — Jamiec
– Jamiec, Commented Jul 1, 2021 at 14:32

Patrick Magee · Accepted Answer · 2021-07-01 14:30:25Z

The JSON you provided is not valid for me to parse, so ive made an assumption to demonstrate. which wraps your sample in a root JSON object.

You can query the JOBject using keys. i.e to access cars propery in the JSON you can use o["cars"]. With this approach you can see i use a bit of Linq to figure out if Audi is red, and if so, you can perform direct modifications to the o object and set values accordingly.

This is the most basic approach, without any further code.

void Main()
{
    var json = @"
    {
        ""cars"": [
            { ""id"": 1, ""make"": ""Audi"", ""color"": ""red"" }, 
            { ""id"": 2, ""make"": ""Mercedes"", ""color"": ""red"" }, 
            { ""id"": 3, ""make"": ""Ford"", ""color"": ""yellow"" }
        ]
    }";

    var jObject = Newtonsoft.Json.Linq.JObject.Parse(json);
    var jArray = jObject["cars"] as JArray;

    Console.WriteLine("Before: " + JsonConvert.SerializeObject(jObject));

    var audiIsRed = jArray.Any(car => car.Value<string>("make").Equals("Audi") && car.Value<string>("color").Equals("red"));

    if (audiIsRed)
    {
        jArray.First(c => c.Value<string>("make").Equals("Ford"))["color"] = "red";
    }

    Console.WriteLine("After: " + JsonConvert.SerializeObject(jObject));
}

An alternative could be making a POCO to deserialize the results, which would contain, for example a List<Car> and then you could do all modifications with C# and no JSON.NET then serialize that result back to JSON.

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