JSON Deserialization Made Simple With System.Web.Helpers and List<dynamic>

Been playing with WebMatrix and have come across some crazy and beautiful code that I really liked in the FourSquare helper on CodePlex. Check this method out, which returns a graph of friends from the fourquare api

/// Returns a list of friends
    /// </summary>
    /// <param name="accessToken">The access token of the authenticating user.</param>
    /// <param name="userId">The Id of the person for whom to pull a friend graph. if not specified, the authenticating user's list of friends will be returned.</param>
    public static IList<dynamic> GetFriends(string accessToken, int userId = 0) {
        var url = "https://api.foursquare.com/v2/users/{0}/friends?oauth_token={1}";

        var client = new WebClient();
        var jsonResult = client.DownloadString(string.Format(url, userId == 0 ? "self" : userId.ToString(), accessToken));
        var result = Json.Decode(jsonResult);
        
        return new List<dynamic>(result.response.friends.items);
    }

Notice how tight this code is. And note the crazy dynamic typing that C#4 provides in combination with the Json.Decode method. If you are wondering where that JSON.Decode method came from, it is from System.Web.Helpers -- you can use this dll anywhere, doesn't have to be with WebMatrix or Razor. Here's a link to the docs on System.Web.Helpers.Json: http://msdn.microsoft.com/en-us/library/system.web.helpers.json(VS.99).aspx 

 Serialization and JSON have long been painful in .NET because of .NET's strong typing.  This got better with the C# dynamic keyword (see this post and this post) but nothing is as elegant as the code above.

Check this example out, which returns a user's FourSquare badges:

/// <summary>
    /// Returns badges for a given user.
    /// </summary>
    /// <param name="accessToken">The access token of the authenticating user</param>
    /// <param name="userId">The Id of the user</param>
    public static IList<dynamic> GetBadges(string accessToken, int userId = 0) {
        var url = "https://api.foursquare.com/v2/users/{0}/badges?oauth_token={1}";
        
        var client = new WebClient();
        var jsonResult = client.DownloadString(string.Format(url, userId == 0 ? "self" : userId.ToString(), accessToken));
        var result = Json.Decode(jsonResult);
        
        var badges = new List<dynamic>();
        var groups = new List<dynamic>(result.response.sets.groups);
        var allBadgesGroup = groups.FirstOrDefault(g => g.type == "all");
		if (allBadgesGroup != null) {
			foreach(var badgeId in allBadgesGroup.items) {
				badges.Add(result.response.badges[badgeId]);
			}
		}
        
        return badges;
    }

Notice how the two dynamic lists get created which are then manipulated with a LINQ lambda query.  Nice! Having dealt so often with either manually mapping JSON to CLR objects and/or dealing with arrays nested in arrays nested in arrays, I'm absolutely loving this.