Deserializing JSON with numeric string keys in C#

Question

{
  Items: [
    {
      "title": "Object1",
      "preview": {
        "2048": "preview_9212.jpg",
        "1024": "preview_6693.jpg",
      }
    },
    {
      "title": "Object2",
      "preview": {
        "2048": "preview_9888.jpg",
        "1024": "preview_6890.jpg",
      }
    },
    {
      "title": "Object3",
      "preview": {
        "2048": "preview_9822.jpg",
        "1024": "preview_6848.jpg",
      }
    }
  ]
}

I usually deserialise like this:

[Serializable]
public class JsonParser
{
    public string title;
    public List<Preview> preview;
}

[Serializable]
class Preview
{
    public string 2048;
}

But since 2048 is an Integer is not possible to use this way. I tried to deserialize the JSON to get preview like these:

public class Preview
{
  [JsonProperty("2048")]
  public string imageNumber { get; set; }
}

var user = JsonConvert.DeserializeObject<Preview>(jsonValue);

or

var json = JObject.Parse(jsonValue);
var preview = json["preview"].ToObject<Dictionary<string, string>>();
foreach (var entry in preview)
{
    Debug.Log(entry.Key);
    Debug.Log(entry.Value);
}

I got: NullReferenceException: Object reference not set to an instance of an object.

I also tried Deserializing JSON that has an int as a key in C# but again NullReferenceException;

Thanks for any help!

The JsonProperty attribute doesn't do what you think it does. You need to deserialize the whole thing, and then get the data you want from the deserialized object. — Robert Harvey, Feb 08 '22 at 14:49
your json string has much more nested levels than your coded types. maybe you can try some **json path**. — Lei Yang, Feb 08 '22 at 14:50
Have a look [here](https://stackoverflow.com/questions/37335030/deserialize-part-of-json-string-array-in-c-sharp) and [here](https://www.newtonsoft.com/json/help/html/SerializingJSONFragments.htm). — Robert Harvey, Feb 08 '22 at 14:53
@RobertHarvey the problem is on those ones the key is not an Integer. — A9191, Feb 08 '22 at 15:02
if the problem is about int keys, you should paste a much simpler json, e.g. `{"1":"a"}` don't mess up our mind with unrelated things. — Lei Yang, Feb 08 '22 at 15:18
The JSON shown is invalid (no quotes around `Items`), and will be difficult to deserialize because of differing property names (two of the objects have `"title"`, one has `"type"`). Please edit your title, as there are no integer keys; there are numeric string keys. Similar problem, different description. — Heretic Monkey, Feb 08 '22 at 15:48

Serge · Accepted Answer · 2022-02-08T15:59:59.383

Since you have numeric string properties, you have 2 main choices:

Use something like [JsonProperty("2048")] and select valid name for the property
Or use a dictionary. This looks much more flexible for me, so you can try this code

Data data= JsonConvert.DeserializeObject<Data>(json);

string preview2048 = data.Items[0].Preview["2048"];  //preview_9212.jpg

or more complicated search using Linq

string  obj3Preview2048 = data.Items.Where(i=> i.Title == "Object3")
.Select(i =>i.Preview["2048"]).FirstOrDefault(); //preview_9822.jpg

classes

public partial class Data
{
    [JsonProperty("Items")]
    public List<Item> Items { get; set; }
}

public partial class Item
{
    [JsonProperty("title", NullValueHandling = NullValueHandling.Ignore)]
    public string Title { get; set; }

    [JsonProperty("token")]
    public string Token { get; set; }

    [JsonProperty("preview")]
    public Dictionary<string, string> Preview { get; set; }
}

and you have some typos in json you posted, and I fix "type" to "title" in one of json objects. This is a fixed version

{
    "Items": [{
            "title": "Object1",
            "token": "6561b1bbe5f1958848jhgd43d2",
            "preview": {
                "2048": "preview_9212.jpg",
                "1024": "preview_6693.jpg"
            }
        },
        {
            "title": "Object2",
            "token": "4a42eb54648DSFhUI664654d25",
            "preview": {
                "2048": "preview_9888.jpg",
                "1024": "preview_6890.jpg"
            }
        },
        {
            "type": "Object3",
            "token": "3fba64831dghkjgfkl5dfaegoj9",
            "preview": {
                "2048": "preview_9822.jpg",
                "1024": "preview_6848.jpg"
            }
        }
    ]
}

There is no item with a title of "Object3". There is an item with a "type" of "Object3"... Also, they are numeric strings, not numbers. — Heretic Monkey, Feb 08 '22 at 15:52
@HereticMonkey Thanks for mentioning the error. It was a mistake in question. — A9191, Feb 08 '22 at 15:56

Deserializing JSON with numeric string keys in C#

1 Answers1