c# - Converting a JSON.NET JObject's Properties/Tokens into Dictionary Keys

Question

I'm using JSON.NET to parse a JSON reponse from openexhangerates.org server side using .NET. The response contains a nested object ("rates") which has a long list of numeric properties:

    {
    "disclaimer": "Exchange rates provided for informational purposes only, with no guarantee whatsoever of accuracy, validity, availability, or fitness for any purpose; use at your own risk. Other than that, have fun! Usage subject to acceptance of terms: http://openexchangerates.org/terms/",
    "license": "Data sourced from various providers with public-facing APIs; copyright may apply; not for resale; no warranties given. Usage subject to acceptance of license agreement: http://openexchangerates.org/license/",
        "timestamp": 1357268408,
        "base": "USD",
        "rates": {
            "AED": 3.673033,
            "AFN": 51.5663,
            "ALL": 106.813749,
            "AMD": 403.579996,
            etc...
        }
    }

The property names correspond to the currency type (e.g. "USD"). I need to assume that the list of properties can change over time, so I want to convert the object into a Dictionary instead of a corresponding C# object.

So instead of deserializing the JSON object into something like this:

class Rates
{
public decimal AED; // United Arab Emirates Dirham
public decimal AFN; // Afghan Afghani
public decimal ALL; // Albanian Lek
public decimal AMD; // Armenian Dram
// etc...
}

I want to end up with this:

Dictionary<string,decimal>() {{"AED",0.2828},{"AFN",0.3373},{"ALL",2.2823},{"AMD",33.378} // etc...};

How do I do this starting from either the response string or from the JObject produced by calling JObject.Parse(responseString)?

Answer 1

JObject already implements IDictionary<string, JToken>, so I suspect that when you've navigated down to the rates member, you should be able to use:

var result = rates.ToDictionary(pair => pair.Key, pair => (decimal) pair.Value);

Unfortunately it uses explicit interface implementation, which makes this a bit of a pain - but if you go via the IDictionary<string, JToken> interface, it's fine.

Here's a short but complete example which appears to work with the JSON you've provided (saved into a test.json file):

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Newtonsoft.Json.Linq;

class Test
{
    static void Main()
    {
        JObject parsed = JObject.Parse(File.ReadAllText("test.json"));
        IDictionary<string, JToken> rates = (JObject) parsed["rates"];
        // Explicit typing just for "proof" here
        Dictionary<string, decimal> dictionary =
            rates.ToDictionary(pair => pair.Key,
                               pair => (decimal) pair.Value);
        Console.WriteLine(dictionary["ALL"]);
    }
}