ExJSONPath - an Elixir JSONPath library

bettio

I am pleased to announce an initial release ExJSONPath.

ExJsonPath is an Elixir library which allows to query maps (JSON objects) and lists (JSON arrays), using JSONPath expressions.

We decided to implement ExJSONPath while working on Astarte Flow, since we wanted to allow users to query arbitrary JSON objects from their pipelines code.

ExJsonPath allows to query deserialized JSON files [1] using expressions similar to the following:

ExJsonPath.eval(store, "$.store.book[?(@.price > 20)].title")
{:ok, ["The Lord of the Rings"]}

ExJsonPath is not tied to JSON at all, the same kind of JSONPath expression can be used on any Elixir map or list.
Right now, the only hard requirement is that keys must be strings.

Hope you’ll find this useful
Let me know if you have any request/question/feedback.

[1]:

{ "store": {
    "book": [ 
      { "category": "reference",
        "author": "Nigel Rees",
        "title": "Sayings of the Century",
        "price": 8.95
      },
      { "category": "fiction",
        "author": "J. R. R. Tolkien",
        "title": "The Lord of the Rings",
        "isbn": "0-395-19395-8",
        "price": 22.99
      }
    ],
    "bicycle": {
      "color": "red",
      "price": 19.95
    }
  }
}

5 comments

#library #json #exjsonpath #jsonpath

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2023-03-15 16:20:15 UTC

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LostKobrakai

Looks interesting. I took a quick look at the code and it seems you’re recursing the structure manually. I’m wondering if it would make sense to convert to an Access pattern instead, so it could be used with get_in, put_in, … all by implementing one transformation from the JSONPath format to a list of Access accessors.

Post #1

bettio

Thanks for the feedback
I’ll try to focus on your advice as soon as I finished writing more tests. I need to write them since JSONPath is not “strongly specified” so I want to ensure a consistent (and stable) behaviour across different library releases.

Post #2

gregvaughn

Is JSONPath widely used in general? I first encountered it in some other libraries as I was doing some background search before writing my first library, path_express, which more closely adheres to Kernel.get_in/2. I’ve used xpath before and I assume some equivalent ideas. I’m on the fence on whether my library should be more or less JSON focused instead of get_in focused. I hope your insight can help in my decisions.

Post #3

bettio

I know there are several software around that use it (e.g. kubectl).
The syntax is quite well known and there are tutorials, several tools (that allows users to test their expressions) and libraries in several languages.
So it was my first choice since it doesn’t require people to learn a new syntax.
I think you should focus your library to a specific use-case, my use-case was to allow people to write JSON templates and pipelines for arbitrary JSON inputs. As a side effect several kind of maps and lists are now supported by my JSONPath library.
I think I will add support to protocols and funs so I can extend my library to use-cases outside JSON.

Post #4