Addressing JSON in C# dynamically

Question

I wish to write some C# which allows the client to provide a JSON string and query string. The query string would then be used to address values in the JSON object.

For example, if I had this JSON:

{
  "head": "big",
  "fingers": [
    "one", "thumb",
    "two", "ring"
  ],
  "arm": {
    "elbow", "locked"
  }
}

And this query string:

"fingers.two"

I would want to return the value "ring".

Is this (or something like it) possible in C#?

I have tried using the ExpandoObject class, but this does not allow dynamic runtime inspection:

var json = JsonConvert.DeserializeObject<ExpandoObject>(jsonStr);

As far as I can tell, the discovery of values on the json variable needs to be done at code time, rather than runtime, which means I cannot dynamically find values being queried for.

Maybe this has the answer you need: Deserialize JSON into C# dynamic object? — Catalin
– Catalin, Commented Aug 7, 2019 at 12:19
Have you considered JSON queries using JSONPath etc? There's a tool here that uses those technologies jsonquerytool.com (JSONPath is built into JSON.Net - newtonsoft.com/json/help/html/QueryJsonSelectTokenJsonPath.htm) — Charleh
– Charleh, Commented Aug 7, 2019 at 12:23
@catalin I don't think so because I want to specify the value to be retrieved as a string, rather than code. — Matt W
– Matt W, Commented Aug 7, 2019 at 12:27
@charleh Thank you - I had forgotten about that class. :) Would you like to post an answer so I can accept it? — Matt W
– Matt W, Commented Aug 7, 2019 at 12:38

Charleh · Accepted Answer · 2019-08-07 12:42:40Z

1

JSONPath does this

Assuming the following JSON (fixed a few syntax errors in the original)

{
  "head": "big",
  "fingers": {
    "one":"thumb",
    "two":"ring"
  },
  "arm": {
    "elbow": "locked"
  }
}

And this query

MyJObjectOrToken.SelectToken("fingers.two")

You will get the following output:

[
    "ring"
]

It should be trivial then to extract the value as a string using JSON.Net methods and return the result to your user.

Support for JSONPath is built into JSON.Net

https://www.newtonsoft.com/json/help/html/SelectToken.htm

answered Aug 7, 2019 at 12:42

Charleh

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