Deserializing via JSON.NET with Variable Property Name

Question

Given some json that looks like

{
  "id":"123_678",
  "fs_123_678":
   {
     "title":"Apple Parts",
     "data": 134
   }
}

I'd like to deserialize it into the following classes

public class Result
{
   public string Id {get; set;}
   public ResultInfo Info {get; set;}
}

public class ResultInfo
{
   public string Title {get; set;}
   public int Data {get; set;}
}

... but that second property (fs_123_678) is not a fixed name. I've looked at other similar posts on SO here, and the common solution is to use a IDictionary<string, MyPoco> however, that only works when the variable data is not at the root level. The name of the property is 100% predictable, and I could describe in code what it will be for a given JSON response based off of values used in the source HTTP request. The trick is, how do I let the JSON deseralizer in on the business rule around what it will be called for this given deserialization? I basically need something that would act like [JsonProperty(PropertyName = *insert logic here*)] (which of course isn't possible).

What's a reasonable way to approach this, all while retaining the "for free" strong-typed deserialization of the rest of the object?

I'd write a custom deserializer (JSON.NET has a great article about it on their site). — Sam Axe
– Sam Axe, Commented Aug 23, 2017 at 0:27
@SamAxe awesome, I was looking in the "Serializing and Deserializing JSON" section (newtonsoft.com/json/help/html/SerializingJSON.htm) and I didn't see anything that would help me out - but maybe I missed it? Got a handy dandy link by chance? — ckittel
– ckittel, Commented Aug 23, 2017 at 0:55
You could use [JsonTypedExtensionData] and TypedExtensionDataConverter<ResultInfo> from How to deserialize a child object with dynamic (numeric) key names?. Or you could write a custom JsonConverter for Result as shown in, say, this answer or this one. — dbc
– dbc, Commented Aug 23, 2017 at 1:17
Can someone link to the "similar" posts? I've also searched, but I can't find them, and it sounds like I can use dictionaries but its not clear how to me. — James Hurley
– James Hurley, Commented Jul 20, 2022 at 12:58

ckittel · Accepted Answer · 2017-08-23 14:31:38Z

Based on the links that dbc provided in comments, I found that this solution appears to be functional, but open to other suggestions. I'm bascially taking the current reader stream, loading it as a JObject then replacing the original JProperty with another that has the name my model is expecting.

public class MyCustomResultConverter : JsonConverter
{
    public override bool CanWrite => false;
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        var obj = JObject.Load(reader);
        var formData = obj.SelectToken("fs_" + obj.SelectToken("id").Value<string>());
        formData.Parent.Replace(new JProperty("info", formData));

        existingValue = existingValue ?? new FormActionResult();
        serializer.Populate(obj.CreateReader(), existingValue);
        return existingValue;
    }

    public override bool CanConvert(Type objectType)
    {
        return typeof(Result).GetTypeInfo().IsAssignableFrom(objectType);
    }
}

[JsonConverter(typeof(MyCustomResultConverter))]
public class Result
{
   public string Id {get; set;}
   public ResultInfo Info {get; set;}
}

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