C# JSON.Net parse and get list of all elements matching a value using LINQ

Question

I'm having trouble finding the correct method for getting a list of json arrays from JObject.
_name element inside the array should be equal to foo.

This is the sample json:

{
    "doc": [{
        "bob": [{
            "tom": [{
                "frank": [{
                    "category": [{
                        "_name": "foo",
                        "letters": "abc"
                    },
                    {
                        "_name": "foo",
                        "letters": "def"
                    },
                    {
                        "_name": "foo",
                        "letters": "ghi"
                    },
                    {
                        "_name": "foo",
                        "letters": "jkl"
                    }]
                }]
            }]
        }]
    }]
}

And here's my code so far:

JObject o = JObject.Parse(File.ReadAllText(@"D:/Client/data.json"));

var results = from x in o["doc"].Children()
              where x["_name"].Value<string>() == "foo"
              select x;

I get this error:

"Value cannot be null.\r\nParameter name: source"

How do I get a list in which each element will be an array containing "_name" and "letters"?

Is it really your intention to have doc.bob be an array containing an object with a property tom which has a property frank? — Steve Ruble
– Steve Ruble, Commented Aug 10, 2014 at 17:14
It's not mine JSON, it's from somewhere else. I simplified it. I get it as Json feed every couple of seconds. — VixinG
– VixinG, Commented Aug 10, 2014 at 17:22

Jon Skeet · Accepted Answer · 2014-08-10 17:13:22Z

5

Three problems:

You don't want the direct children of doc, you want the descendants.
You're using x["_name"].Value<string>() even if there is no _name property
You're using x["_name"].Value<string>() even on non-object children

These are all easily fixed though:

var doc = (JContainer) o["doc"];
var results = doc.Descendants()
                 .OfType<JObject>()
                 .Where(x => x["_name"] != null &&
                             x["_name"].Value<string>() == "foo");

answered Aug 10, 2014 at 17:13

Jon Skeet

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1 Comment

VixinG Over a year ago

Great, thank you. I must have misunderstood, because in documentation it says: "Returns a collection of child tokens of every array in the source collection." and I thought "child tokens of every array" will work.

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