c# parse json value, check if null

Question

So I have this Web API that calls a service which in turn, returns a json string. The string looks a bit like this:

{
    "title": "Test",
    "slug": "test",
    "collection":{  },
    "catalog_only":{  },
    "configurator":null
}

I have cut this down considerably to make it easier to see my issue.

When I make my API call, I then use a Factory method to factorize the response which looks something like this:

    /// <summary>
    /// Used to create a product response from a JToken
    /// </summary>
    /// <param name="model">The JToken representing the product</param>
    /// <returns>A ProductResponseViewModel</returns>
    public ProductResponseViewModel Create(JToken model)
    {

        // Create our response
        var response = new ProductResponseViewModel()
        {
            Title = model["title"].ToString(),
            Slug = model["slug"].ToString()
        };

        // Get our configurator property
        var configurator = model["configurator"];

        // If the configurator is null
        if (configurator == null)
            throw new ArgumentNullException("Configurator");

        // For each item in our configurator data
        foreach (var item in (JObject)configurator["data"])
        {

            // Get our current option
            var option = item.Value["option"].ToString().ToLower();

            // Assign our configuration values
            if (!response.IsConfigurable) response.IsConfigurable = (option == "configurable");
            if (!response.IsDesignable) response.IsDesignable = (option == "designable");
            if (!response.HasGraphics) response.HasGraphics = (option == "graphics");
            if (!response.HasOptions) response.HasOptions = (option == "options");
            if (!response.HasFonts) response.HasFonts = (option == "fonts");
        }

        // Return our Product response
        return response;
    }
}

Now, as you can see I am getting my configurator property and then checking it to see if it's null. The json string shows the configurator as null, but when I put a breakpoint on the check, it actually shows it's value as {}. My question is how can I get it to show the value (null) as opposed to this bracket response?

Jon Skeet · Accepted Answer · 2015-06-08 10:15:01Z

18

You're asking for the JToken associated with the configurator key. There is such a token - it's a null token.

You can check this with:

if (configurator.Type == JTokenType.Null)

So if you want to throw if either there's an explicit null token or configurator hasn't been specified at all, you could use:

if (configurator == null || configurator.Type == JTokenType.Null)

answered Jun 8, 2015 at 10:15

Jon Skeet

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Comments

Amir Mahdi Nassiri · Accepted Answer · 2021-07-22 16:15:29Z

16

For those who use System.Text.Json in newer .Net versions (e.g. .Net 5):

var jsonDocument = JsonDocument.Parse("{ \"configurator\": null }");
var jsonElement = jsonDocument.RootElement.GetProperty("configurator");

if (jsonElement.ValueKind == JsonValueKind.Null)
{
    Console.WriteLine("Property is null.");
}

answered Jul 22, 2021 at 16:15

Amir Mahdi Nassiri

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Comments

Amit Kumar Ghosh · Accepted Answer · 2015-06-08 10:25:09Z

    public class Collection
    {
    }

    public class CatalogOnly
    {
    }

    public class RootObject
    {
        public string title { get; set; }
        public string slug { get; set; }
        public Collection collection { get; set; }
        public CatalogOnly catalog_only { get; set; }
        public object configurator { get; set; }
    }

    var k = JsonConvert.SerializeObject(new RootObject
                {
                    catalog_only =new CatalogOnly(),
                    collection = new Collection(),
                    configurator =null,
                    slug="Test",
                    title="Test"
                });

    var t = JsonConvert.DeserializeObject<RootObject>(k).configurator;

Here configurator is null.

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