On Mon, Oct 1, 2018 at 11:50 AM Ihor Radchenko <yantar92@gmail.com> wrote:

Hello Ihor,

That code is perfect!

I was able to get what I want with minor refactoring. Thanks!

Refactored code:

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(defvar org-concatenated-properties '("AA")
  "List of property names whose values are allowed to be concatenated.
The list is of type '(PROP1 PROP2 ..) where each element is a string.")

(defvar org-property-concat-string "/"
  "String use to concat the `org-concatenated-properties' properties.")

(defun org-get-parent-property (property inherit literal-nil)
  "Get the value of PROPERTY from the parent relative to current point."
  (org-with-wide-buffer
   (if (org-up-heading-safe)
       (or (org-entry-get nil property inherit literal-nil) "")
     "")))

(defun org/advice-concatenate-properties-maybe (orig-fun &rest args)
  "Concatenate an Org Property value with its inherited value.
The concatenation happens only if the Org Property is in
`org-concatenated-properties' list."
  (let* ((value-orig (apply orig-fun args))
         (property (nth 1 args))
         (dont-concat (not (member property org-concatenated-properties))))
    ;; (message "dbg: args:%S value-orig:%S property:%S" args value-orig property)
    (if dont-concat
        value-orig
      (let* ((pom (nth 0 args))
             (inherit (nth 2 args))
             (literal-nil (nth 3 args))
             (value-here-no-inherit (apply orig-fun `(,pom ,property nil ,literal-nil)))
             (value-parent (apply #'org-get-parent-property `(,property ,inherit ,literal-nil))))
        ;; (message "dbg advice: value-here-no-inherit: %S" value-here-no-inherit)
        (if value-here-no-inherit
            (format "%s%s%s"
                    value-parent
                    (if (org-string-nw-p value-parent)
                        org-property-concat-string
                      "")
                    value-orig)
          value-parent)))))
(advice-add 'org-entry-get :around #'org/advice-concatenate-properties-maybe)
;; (advice-remove 'org-entry-get #'org/advice-concatenate-properties-maybe)

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Example Org file:

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* heading 1
:PROPERTIES:
:FOO:      abc
:END:

asdf
** heading 1
:PROPERTIES:
:FOO: def
:AA: pqr
:END:
*** heading 2
:PROPERTIES:
:FOO: 123
:AA: 456
:END:
**** heading 3
=====