QueryingLINQtoJSON.md

Querying JSON with LINQ

LINQ to JSON provides methods for getting data from its objects. The index methods on JObject/JArray supports quickly get data by its property name on an object or index in a collection, while Argon.JToken.Children allows the retrieval of ranges of data as IEnumerable<JToken> to then query using LINQ.

Getting values by Property Name or Collection Index

The simplest way to get a value from LINQ to JSON is to use the Argon.JToken.Item(System.Object) index on JObject/JArray and then cast the returned Argon.JValue to the type required.

var json = """
           {
             'channel': {
               'title': 'James Newton-King',
               'link': 'http://james.newtonking.com',
               'description': 'James Newton-King\'s blog.',
               'item': [
                 {
                   'title': 'Json.NET 1.3 + New license + Now on CodePlex',
                   'description': 'Announcing the release of Json.NET 1.3, the MIT license and the source on CodePlex',
                   'link': 'http://james.newtonking.com/projects/json-net.aspx',
                   'categories': [
                     'Json.NET',
                     'CodePlex'
                   ]
                 },
                 {
                   'title': 'LINQ to JSON beta',
                   'description': 'Announcing LINQ to JSON',
                   'link': 'http://james.newtonking.com/projects/json-net.aspx',
                   'categories': [
                     'Json.NET',
                     'LINQ'
                   ]
                 }
               ]
             }
           }
           """;

var rss = JObject.Parse(json);

var rssTitle = (string) rss["channel"]["title"];
// James Newton-King

var itemTitle = (string) rss["channel"]["item"][0]["title"];
// Json.NET 1.3 + New license + Now on CodePlex

var categories = (JArray) rss["channel"]["item"][0]["categories"];
// ["Json.NET", "CodePlex"]

var categoriesText = categories
    .Select(c => (string) c)
    .ToList();
// Json.NET
// CodePlex

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Querying with LINQ

JObject/JArray can also be queried using LINQ. Argon.JToken.Children returns the children values of a JObject/JArray as an IEnumerable<JToken> that can then be queried with the standard Where/OrderBy/Select LINQ operators.

Argon.JToken.Children returns all the children of a token. If it is a JObject it will return a collection of properties to work with, and if it is a JArray a collection of the array's values will be returned.

var postTitles =
    (
        from p in rss["channel"]["item"]
        select (string) p["title"]
    )
    .ToList();

foreach (var item in postTitles)
{
    Console.WriteLine(item);
}

//LINQ to JSON beta
//Json.NET 1.3 + New license + Now on CodePlex

var categories =
    (
        from c in rss["channel"]["item"]
            .SelectMany(_ => _["categories"])
            .Values<string>()
        group c by c
        into g
        orderby g.Count() descending
        select new
        {
            Category = g.Key,
            Count = g.Count()
        }
    )
    .ToList();

foreach (var c in categories)
{
    Console.WriteLine($"{c.Category} - Count: {c.Count}");
}

//Json.NET - Count: 2
//LINQ - Count: 1
//CodePlex - Count: 1

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LINQ to JSON can also be used to manually convert JSON to a .NET object.

public class Shortie
{
    public string Original { get; set; }
    public string Shortened { get; set; }
    public string Short { get; set; }
    public ShortieException Error { get; set; }
}

public class ShortieException
{
    public int Code { get; set; }
    public string ErrorMessage { get; set; }
}

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Manually serializing and deserializing between .NET objects is useful when working with JSON that doesn't closely match the .NET objects.

var jsonText = """
               {
                 'short': {
                   'original': 'http://www.foo.com/',
                   'short': 'krehqk',
                   'error': {
                     'code': 0,
                     'msg': 'No action taken'
                   }
                 }
               }
               """;

var json = JObject.Parse(jsonText);

var shortie = new Shortie
{
    Original = (string) json["short"]["original"],
    Short = (string) json["short"]["short"],
    Error = new()
    {
        Code = (int) json["short"]["error"]["code"],
        ErrorMessage = (string) json["short"]["error"]["msg"]
    }
};

Console.WriteLine(shortie.Original);
// http://www.foo.com/

Console.WriteLine(shortie.Error.ErrorMessage);
// No action taken

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Related Topics

• LINQtoJSON
• Argon.JToken.Item(System.Object)
• Argon.JToken.Children