How to use jq-mode to query JSON in org-mode?

Question

I wanted to use jq in org-mode to query JSON, and saw a jq-mode that supports org-babel:

jq-mode provides ob-jq for working with literate programming in Org mode.

Add jq under org-babel-load-languages in your .emacs file

(org-babel-do-load-languages 'org-babel-load-languages
                             '((jq . t)))

I changed my org-mode configuration, but I am not sure how to use the jq support. There are no usage examples in the documentation. I guess I am missing something obvious due to my lack of knowledge about how code blocks work.

In the command line, jq should be used as:

$ cat a.json | jq '.[] | [.id]'
[
  1
]
[
  2
]

, where a.json is a JSON file with the following content:

[
    {
        "id": 1,
        "details": {
            "username": "jamesbrown",
            "name": "James Brown"
        }
    }
    , {
        "id": 2,
        "details": {
            "username": "johnsmith",
            "name": "John Smith"
        }
    }
]

In my initial attempt to do this query in org-mode, I added the following block with the jq filter .[] | [.id] in it:

#+begin_src jq
  .[] | [.id]
#+end_src

Then, I don't know how to provide the JSON input to jq. If I press C-c C-c on the code block, I just get an empty:

#+RESULTS:

My questions are:

How can I provide input or more generally, what is the intended way to use jq in org?

*How can I save the result JSON or text string from jq to a file?

(Ideally, I'd like to have the input to be some data/code block embedded inside the same org file, for readability)

Answer 1

For input, you can use the :in-file header:

#+begin_src jq :results drawer :in-file a.json
  .[] | [.id]
#+end_src

For input and output, you can specify a :cmd-line header:

#+begin_src jq :results drawer :cmd-line < a.json > b.json
   .[] | [.id]
#+end_src

It can also accept a :var param through which you can pass arguments, but I don't know enough about jq to tell you how to use it: it uses the --arg command line switch however - maybe you know how to use that switch and can answer that part of the question?

I got that much by reading ob-jq.el, guessing and experimenting; but it does need proper documentation. Maybe you can write some and add it to Worg? Or submit it to the GitHub site?