How to modify content of org-mode document using org-element API?

Question

Let's say I have an org-mode file at ~/myorg.org, looking like this:

* TODO My TODO list
** TODO Play games
** TODO Build a boat
** DONE Do something else

Now I want to modify this document using org-element. Let's say I want to change all TODO items to DONE. I thought something like this would work:

(with-current-buffer (find-file-noselect "~/myorg.org") 
  (org-element-map (org-element-parse-buffer) 'headline
    (lambda (h)
      (org-element-put-property h :todo-keyword "DONE")))
  (save-buffer))

The structure returned from org-element-map seems fine, but the code doesn't modify the file. Do I have to replace the whole buffer text using org-element-interpret-data, or is there some other way?

Answer 1

The org-element-put-property command does not modify the buffer content, it just returns the new element.

I would approach your use case differently: call save-excursion, then jump to the top of the buffer (or region, etc). Move forward using outline-next-heading. At each heading you can call org-entry-is-todo-p and (org-todo 'done) to mark each one done. Then save the buffer.

More generally: if you want to use the org-element API to apply changes, I think you are correct that you would need to call org-element-interpret-data to convert the updated AST back to text and then replace the buffer content. See http://orgmode.org/worg/dev/org-element-api.html.

Answer 2

Here is one solution using org-map-entries. If you do C-c C-c on the source code block it will change all TODO entries to DONE in the current buffer. One caveat is that if you have DONE with @ (e.g., "DONE(d@)") in org-todo-keywords, then the last entry's change will invoke note taking for the change, and I'm not sure how to suppress it. I guess pressing C-c C-k once is not too bad.

#+BEGIN_SRC emacs-lisp :results none
(let ((MATCH "/+TODO")
      (SCOPE nil)
      (SKIP nil)
      (spacing nil))

  (org-map-entries
   (lambda () 
       (org-todo 'done))
    MATCH SCOPE SKIP))
#+END_SRC

* TODO My TODO list
** TODO Play games
** TODO Build a boat
** DONE Do something else