How to do recursive descent of json using json.net?

Question

I am trying to parse a json file using json.net. The file looks like this

{X:
   {
      Title:"foo",
      xxxx:xxxx
   }
}
{Y:
   {ZZ:
        {Title: "bar",...}
    }
}

I am trying to recurse down this structure processing all objects with a Title attribute. But I am confused about JToken, JProperty, JContainer, JValue, JObject. Reading the source code has not left me much wiser and none of the samples help. I want something along the lines of

WalkNode(node, Action<Node> action)
{
    foreach(var child in node.Children)
    {
        Action(child);
        WalkNode(child);
    }
}

Parse()
{
   WalkNode(root, n=>
    {
        if(n["Title"] != null)
        {
           ...
        }
    });
}

Some questions: The above example is not valid JSON. Are the containing objects of properties X and Y supposed to be in an array, or did you intend for X and Y to be in the same containing object? Also, will there be arrays anywhere in the JSON hierarchy that you need to traverse, or is it just nested objects and properties? — Brian Rogers
– Brian Rogers, Commented Apr 25, 2013 at 5:49

Brian Rogers · Accepted Answer · 2013-04-25 06:39:26Z

35

The code below should be pretty close to what you are looking for. I made the assumption that there is an outer array, and that arrays can appear anywhere in the hierarchy. (If this is not true, you can simplify the WalkNode method code a bit, but it should work either way.)

using System;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;

namespace JsonRecursiveDescent
{
    class Program
    {
        static void Main(string[] args)
        {
            string json =
            @"[
                {
                    ""X"":
                    {
                        ""Title"":""foo"",
                        ""xxxx"":""xxxx""
                    }
                },
                {
                    ""Y"":
                    {
                        ""ZZ"":
                        {
                            ""Title"":""bar"",
                            ""xxxx"":""xxxx""
                        }
                    }
                }
            ]";

            JToken node = JToken.Parse(json);

            WalkNode(node, n =>
            {
                JToken token = n["Title"];
                if (token != null && token.Type == JTokenType.String)
                {
                    string title = token.Value<string>();
                    Console.WriteLine(title);
                }
            });
        }

        static void WalkNode(JToken node, Action<JObject> action)
        {
            if (node.Type == JTokenType.Object)
            {
                action((JObject)node);

                foreach (JProperty child in node.Children<JProperty>())
                {
                    WalkNode(child.Value, action);
                }
            }
            else if (node.Type == JTokenType.Array)
            {
                foreach (JToken child in node.Children())
                {
                    WalkNode(child, action);
                }
            }
        }

    }
}

answered Apr 25, 2013 at 6:39

Brian Rogers

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2 Comments

rodolfoprado Over a year ago

But if I don't know that "Title" exists and I want all the properties?

Brian Rogers Over a year ago

That is a different question. If you want to post a new question describing what you're trying to do, I will be happy to answer it. Be sure to tag it json.net.

TheRisingEdge · Accepted Answer · 2017-05-07 20:08:25Z

24

Also needed to do something of the sorts. Would like to propose my solution. It has the advantage of:

not being recursive
no callbacks
not assuming any internal structure (arrays)

decouples tree traversal from the action needed to be executed

IEnumerable<JToken> AllTokens(JObject obj) {
    var toSearch = new Stack<JToken>(obj.Children());
    while (toSearch.Count > 0) {
        var inspected = toSearch.Pop();
        yield return inspected;
        foreach (var child in inspected) {
            toSearch.Push(child);
        }
    }
}

Then you can use linq to filter and perform action:

var tokens = AllTokens(jsonObj);
var titles = tokens.Where(t => t.Type == JTokenType.Property && ((JProperty)t).Name == "Title");

answered May 7, 2017 at 20:08

TheRisingEdge

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1 Comment

Kiquenet Over a year ago

how-to lowername all nodes from json string or JObject ?

Thymine · Accepted Answer · 2013-11-20 17:17:52Z

I thought I'd include my minor tweaks to @BrianRogers WalkNode method, made it slightly more versatile:

private static void WalkNode(JToken node,
                                Action<JObject> objectAction = null,
                                Action<JProperty> propertyAction = null)
{
    if (node.Type == JTokenType.Object)
    {
        if (objectAction != null) objectAction((JObject) node);

        foreach (JProperty child in node.Children<JProperty>())
        {
            if (propertyAction != null) propertyAction(child);
            WalkNode(child.Value, objectAction, propertyAction);
        }
    }
    else if (node.Type == JTokenType.Array)
    {
        foreach (JToken child in node.Children())
        {
            WalkNode(child, objectAction, propertyAction);
        }
    }
}

Then OP could do something like:

WalkNode(json, null, prop =>
{
     if (prop.Name == "Title" && prop.Value.Type == JTokenType.String)
     {
         string title = prop.Value<string>();
         Console.WriteLine(title);
     }
});

asgerhallas · Accepted Answer · 2019-06-24 08:14:49Z

9

You could also do it with JSONPath: node.SelectTokens("$..*");

Used like this:

var jObjectsWithTitle = node
    .SelectTokens("$..*")
    .OfType<JObject>()
    .Where(x => x.Property("Title") != null);

Or just:

var jObjectsWithTitle = node.SelectTokens("$..[?(@.Title)]");

edited Jun 24, 2019 at 8:14

answered Jun 24, 2019 at 6:57

asgerhallas

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Comments

marsnebulasoup · Accepted Answer · 2021-07-11 16:18:43Z

1

Try this Method I have written it after some unsuccessful tries:

 private void Traverse(JToken token, TreeNode tn)
    {
        if (token is JProperty)
            if (token.First is JValue)
                tn.Nodes.Add(((JProperty)token).Name + ": " + ((JProperty)token).Value);
            else
                tn = tn.Nodes.Add(((JProperty)token).Name);

        foreach (JToken token2 in token.Children())
            Traverse(token2, tn);
    }

You first have to pass it the complete JSON file like this:

TreeNode rooty= tvu.Nodes.Add("Rooty") // not the Indian bread,just Rooty,  Ok?
JToken token = JToken.Parse(File.ReadAllText(<"Path to json file">));
Traverse(token, rooty);

Done, Boom you got this one: Oh no, I am not allowed to embed pictures. sad.

edited Jul 11, 2021 at 16:18

marsnebulasoup

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answered Dec 15, 2015 at 16:26

Abubaker Hamid

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Comments

EricCodebot · Accepted Answer · 2021-04-02 16:10:07Z

I wrapped the data with a "root" node, and wrapped it all as an array value. Then this works for me:

    private static void TraverseJson(string jsonText)
    {
        dynamic jsonObject = JsonConvert.DeserializeObject(jsonText);

        JArray ja = (JArray)jsonObject.root;
        int itemCount = ja.Count;

        foreach (JObject jobj in jsonObject.root)
        {
            WalkHierarchy(jobj);
        }
    }

    private static void WalkHierarchy(JObject jobj)
    {
        foreach (JProperty jprop in (JToken)jobj)
        {
            if (jprop.Value.Type == JTokenType.Object)
            {
                WalkHierarchy((JObject)jprop.Value);
            }
            else
            {
                Console.WriteLine(jprop.Value.ToString());
            }
        }
    }

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