Deserialize JSON where the property name indicates the type of the value

Question

I'm currently dealing with getting data from an external API. The data I receive looks something like what is shown below. (Just a mockup; don't expect the values to make any sense. It's just to illustrate what kind of data I get.)

{
   "user": [
      {
        "key": "12345678",
        "data": [
          {
            "id": "Name",
            "string": "Bob"
          },
          {
            "id": "ElapsedTimeSinceLastMessage",
            "timestamp": 1618233964000
          },
          {
            "id": "Age",
            "number": 27
          }
        ]
      }
   ]
}

I don't really know how I should be going about deserializing this JSON.

The classes I'm using to deserialize right now look like this:

public class User
{
    [JsonProperty("key")]
    public string Key { get; set; }

    [JsonProperty("data")]
    public List<DataEntry> DataEntries { get; set; }
}

public class DataEntry
{
    [JsonProperty("id")]
    public string Id { get; set; }

    public Type Value { get; set; }
}

And I don't know what I need to set in order to deserialize the Value inside the DataEntry. Maybe someone can guide me into the right direction?

Answer 1

The Data part of this JSON is really just a Dictionary<string, object> in disguise. You can use a custom JsonConverter to transform the list of id/value pairs into that format for easy use.

Frist, define these classes:

class RootObject
{
    [JsonProperty("user")]
    public List<User> Users { get; set; }
}

class User
{
    public string Key { get; set; }

    [JsonConverter(typeof(CustomDataConverter))]
    public Dictionary<string, object> Data { get; set; }
}

Next, define the converter:

class CustomDataConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(Dictionary<string, object>);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        return JToken.Load(reader)
            .Children<JObject>()
            .ToDictionary(jo => (string)jo["id"],
                          jo => jo.Properties()
                                  .Where(jp => jp.Name != "id" && jp.Value is JValue)
                                  .Select(jp => ((JValue)jp.Value).Value)
                                  .FirstOrDefault());
    }

    public override bool CanWrite => false;

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

You can then deserialize and dump out the data like this:

var root = JsonConvert.DeserializeObject<RootObject>(json);
foreach (User user in root.Users)
{
    Console.WriteLine("User Key: " + user.Key);
    foreach (var kvp in user.Data)
    {
        Console.WriteLine(kvp.Key + ": " + kvp.Value);
    }
}

Here is a working demo: https://dotnetfiddle.net/GIT4dl

Answer 2

One angle of attack would be with Dictionaries:

public class WithUser
{
    public List<User> User { get; set; }

}

public class User
{
    [JsonProperty("key")]
    public string Key { get; set; }

    [JsonProperty("data")]
    public List<Dictionary<string,object>> DataEntries { get; set; }
}

The extraction is a bit of a pain but possible:

public static void Main()
{
    var json = File.ReadAllText("Example.json");
    var x = JsonConvert.DeserializeObject<WithUser>(json);

    var user = x.User.Single();
    var age = Extract<long>(user, "Age");
    var name = Extract<string>(user, "Name");
    var elapsedTimeSinceLastMessage = TimeSpan.FromTicks(Extract<long>(user, "ElapsedTimeSinceLastMessage"));
    
}

public static T Extract<T>(User user, string name)
{
    var o = user.DataEntries
        .SingleOrDefault(d => (string)d["id"] == name) // Find the one with age
        .SingleOrDefault(kvp => kvp.Key != "id") // Find the not 'id' value
        .Value; // Take the value  
    return (T)o;
}