reference unique id across emacs org-mode files

Question

I have several .org files, and I'd like to be able to create links between them using an ID. I am using DOIs as unique identifiers. I can link within a file by using properties:

* Paper 1
  :PROPERTIES:
  :CUSTOM_ID: 10.1088/0953-8984/23/21/213001
  :END:

* Paper 2
  :PROPERTIES:
  :CUSTOM_ID: 10.1038/nphys2935
See also [[#10.1088/0953-8984/23/21/213001]]

Is there a way to make the custom_id global, so I can reference it from another file?

I think that org-id is what I need to go further, but I've found the documentation a little confusing. I tried adding the following lines in my .emacs

;; Use global IDs
(require 'org-id)
(setq org-id-link-to-org-use-id use-existing)

;; Update ID file .org-id-locations on startup
(org-id-update-id-locations)

but the file .emacs.d/.org-id-locations only has nil.

It seems like global links won't be automatically generated (Assign IDs to every entry in Org-mode). I tried (with cursor on the heading) to use M-x org-id-get-create, but this does not seem to do anything.

EDIT: (Based on helpful comment)

Within one session, I can store and create links using M-x org-store-link while on the heading (Paper 1 in my example above). Then I can use M-x org-insert-link, and type the ID to insert the link. The link looks like [[id:10.1088/0953-8984/23/21/213001][Paper 1]]. But I am running into two problems: (1) I'd like the ids to be stored automatically. (2) The links don't work when I close and re-open the file.

EDIT: A related question:

https://emacs.stackexchange.com/questions/2186/have-org-modes-exported-html-use-custom-id-when-linking-to-sub-sections-in-toc

Answer 1

So here's the solution I came up with.

1. In my .emacs configuration, I have kept the same settings as in my question:

   (require 'org-id)
   (setq org-id-link-to-org-use-id use-existing)
   
   ;; Update ID file on startup
   (org-id-update-id-locations)
   

2. The files need to be part of the agenda list (or added to the list of additional files using org-id-extra-files (See org-id documentation))

3. Use ID instead of CUSTOM_ID in the PROPERTIES drawer:

   * Paper 1
     :PROPERTIES:
     :ID: 10.1088/0953-8984/23/21/213001
     :END:
   

4. Each ID needs to be created (if necessary; in my case I already have them), and a link added to the ID file (links are stored in .emacs.d/.org-id-locations). This is done using org-id-get-create: with the cursor on the heading, call it using

   M-x org-id-get-create
   

5. Link to an ID using [[id:10.1088/0953-8984/23/21/213001][Paper 1]].

I have to think a little bit more about when I'd like the ID to be created; I can automate the process by tying the ID storing to another function that I'll do to all the headings.