Write a JsonPath query for a null property with Newtonsoft Json.NET

Question

Given a JSON array of:

[
  {
      "id": 1,
      "name": "abc"
  },
  {
      "id": 2
  },
  {
      "id": 3,
      "name": "def"
  }
]

I would expect:

JArray jArray = JArray.Parse(json);
dynamic value = jArray.SelectTokens("$[?(@['name'] == null || @['name'] == 'abc')]");

to produce:

[
  {
    "id": 1,
    "name": "abc"
  },
  {
    "id": 2
  }
]

This tests correctly using a variety of online JsonPath testers. But when I run it with Json.NET, I am getting:

[
  {
    "id": 1,
    "name": "abc"
  }
]

Is it possible for me to change the JsonPath to handle this? Is it the null in the query that is the problem?

For clarity, I need to use JsonPath because it is stored in a configuration file and applied dynamically.

gregsdennis · Accepted Answer · 2021-09-06 09:21:32Z

2

I expect that Newtsoft is considering absence to be different from "present with a null value," whereas the others you've tried consider them to be the same.

I imagine if you update the path to

$[?(!@['name'] || @['name'] == null || @['name'] == 'abc')]

it might work for you.

Alternatively, updating the data to

[
  {
      "id": 1,
      "name": "abc"
  },
  {
      "id": 2,
      "name": null
  },
  {
      "id": 3,
      "name": "def"
  }
]

would also yield the middle item.

We haven't defined this yet in the specification effort, but it's a good one. I'll raise that in an issue.

You can also see there's no consensus among libraries with this test.

edited Sep 6, 2021 at 9:21

answered Sep 6, 2021 at 5:07

gregsdennis

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2 Comments

Peter Csala Over a year ago

The related github issue

maxmoore14 Over a year ago

Unfortunately Newtonsoft treats ! as an unexpected character if I use that syntax. Good suggestion though.

Peter Csala · Accepted Answer · 2021-09-06 07:47:04Z

0

With LINQ to JSON you can solve the same problem like this:

var json = File.ReadAllText("sample.json");

var semiParsedJson = JArray.Parse(json);
var filteredJson = from item in semiParsedJson
                   let name = (string)item["name"]
                   where name == null || name == "abc"
                   select item;

Console.WriteLine(new JArray(filteredJson));

The output will be as expected:

[
  {
    "id": 1,
    "name": "abc"
  },
  {
    "id": 2
  }
]

answered Sep 6, 2021 at 7:47

Peter Csala

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2 Comments

maxmoore14 Over a year ago

Yes, another good suggestion. In my case, I need to use JsonPath because it is stored in a configuration file and applied dynamically.

Peter Csala Over a year ago

@maxmoore14 Could you please include this valuable information into your question? To avoid further alternative suggestions :D

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