Dynamic org-agenda with org-roam - https://d12frosted.io/posts/2021-01-16-task-management-with-roam-vol5.html

agenda.el

(defun vulpea-project-p ()
  "Return non-nil if current buffer has any todo entry.

TODO entries marked as done are ignored, meaning the this
function returns nil if current buffer contains only completed
tasks."
  (seq-find                                 ; (3)
   (lambda (type)
     (eq type 'todo))
   (org-element-map                         ; (2)
       (org-element-parse-buffer 'headline) ; (1)
       'headline
     (lambda (h)
       (org-element-property :todo-type h)))))

(defun vulpea-project-update-tag ()
    "Update PROJECT tag in the current buffer."
    (when (and (not (active-minibuffer-window))
               (vulpea-buffer-p))
      (save-excursion
        (goto-char (point-min))
        (let* ((tags (vulpea-buffer-tags-get))
               (original-tags tags))
          (if (vulpea-project-p)
              (setq tags (cons "project" tags))
            (setq tags (remove "project" tags)))

          ;; cleanup duplicates
          (setq tags (seq-uniq tags))

          ;; update tags if changed
          (when (or (seq-difference tags original-tags)
                    (seq-difference original-tags tags))
            (apply #'vulpea-buffer-tags-set tags))))))

(defun vulpea-buffer-p ()
  "Return non-nil if the currently visited buffer is a note."
  (and buffer-file-name
       (eq major-mode 'org-mode)
       (string-suffix-p "org" buffer-file-name)
       (string-prefix-p
        (expand-file-name (file-name-as-directory vulpea-directory))
        (file-name-directory buffer-file-name))))

(defun vulpea-project-files ()
    "Return a list of note files containing 'project' tag." ;
    (seq-uniq
     (seq-map
      #'car
      (org-roam-db-query
       [:select [nodes:file]
        :from tags
        :left-join nodes
        :on (= tags:node-id nodes:id)
        :where (like tag (quote "%\"project\"%"))]))))

(defun vulpea-agenda-files-update (&rest _)
  "Update the value of `org-agenda-files'."
  (setq org-agenda-files (vulpea-project-files)))

(add-hook 'find-file-hook #'vulpea-project-update-tag)
(add-hook 'before-save-hook #'vulpea-project-update-tag)

(advice-add 'org-agenda :before #'vulpea-agenda-files-update)
(advice-add 'org-todo-list :before #'vulpea-agenda-files-update)

;; functions borrowed from `vulpea' library
;; https://github.com/d12frosted/vulpea/blob/6a735c34f1f64e1f70da77989e9ce8da7864e5ff/vulpea-buffer.el

(defun vulpea-buffer-tags-get ()
  "Return filetags value in current buffer."
  (vulpea-buffer-prop-get-list "filetags" "[ :]"))

(defun vulpea-buffer-tags-set (&rest tags)
  "Set TAGS in current buffer.

If filetags value is already set, replace it."
  (if tags
      (vulpea-buffer-prop-set
       "filetags" (concat ":" (string-join tags ":") ":"))
    (vulpea-buffer-prop-remove "filetags")))

(defun vulpea-buffer-tags-add (tag)
  "Add a TAG to filetags in current buffer."
  (let* ((tags (vulpea-buffer-tags-get))
         (tags (append tags (list tag))))
    (apply #'vulpea-buffer-tags-set tags)))

(defun vulpea-buffer-tags-remove (tag)
  "Remove a TAG from filetags in current buffer."
  (let* ((tags (vulpea-buffer-tags-get))
         (tags (delete tag tags)))
    (apply #'vulpea-buffer-tags-set tags)))

(defun vulpea-buffer-prop-set (name value)
  "Set a file property called NAME to VALUE in buffer file.
If the property is already set, replace its value."
  (setq name (downcase name))
  (org-with-point-at 1
    (let ((case-fold-search t))
      (if (re-search-forward (concat "^#\\+" name ":\\(.*\\)")
                             (point-max) t)
          (replace-match (concat "#+" name ": " value) 'fixedcase)
        (while (and (not (eobp))
                    (looking-at "^[#:]"))
          (if (save-excursion (end-of-line) (eobp))
              (progn
                (end-of-line)
                (insert "\n"))
            (forward-line)
            (beginning-of-line)))
        (insert "#+" name ": " value "\n")))))

(defun vulpea-buffer-prop-set-list (name values &optional separators)
  "Set a file property called NAME to VALUES in current buffer.
VALUES are quoted and combined into single string using
`combine-and-quote-strings'.
If SEPARATORS is non-nil, it should be a regular expression
matching text that separates, but is not part of, the substrings.
If nil it defaults to `split-string-default-separators', normally
\"[ \f\t\n\r\v]+\", and OMIT-NULLS is forced to t.
If the property is already set, replace its value."
  (vulpea-buffer-prop-set
   name (combine-and-quote-strings values separators)))

(defun vulpea-buffer-prop-get (name)
  "Get a buffer property called NAME as a string."
  (org-with-point-at 1
    (when (re-search-forward (concat "^#\\+" name ": \\(.*\\)")
                             (point-max) t)
      (buffer-substring-no-properties
       (match-beginning 1)
       (match-end 1)))))

(defun vulpea-buffer-prop-get-list (name &optional separators)
  "Get a buffer property NAME as a list using SEPARATORS.
If SEPARATORS is non-nil, it should be a regular expression
matching text that separates, but is not part of, the substrings.
If nil it defaults to `split-string-default-separators', normally
\"[ \f\t\n\r\v]+\", and OMIT-NULLS is forced to t."
  (let ((value (vulpea-buffer-prop-get name)))
    (when (and value (not (string-empty-p value)))
      (split-string-and-unquote value separators))))

(defun vulpea-buffer-prop-remove (name)
  "Remove a buffer property called NAME."
  (org-with-point-at 1
    (when (re-search-forward (concat "\\(^#\\+" name ":.*\n?\\)")
                             (point-max) t)
      (replace-match ""))))

One more question, in case I am using org-roam-dailies, which stores the tasks in individual files within a sub-folder daily within the org-roam folder, do I need to update the function vulpea-agenda-files-update to include the daily folder? Or would it be simpler to modify the capture function for org-roam-dailies-capture-templates to add the project tag?

Vulpea scans the buffer for any todo and adds the project tag automatically. It latches onto before-save hook.

(add-hook 'before-save-hook #'vulpea-project-update-tag)

(defun vulpea-project-update-tag ()
    "Update PROJECT tag in the current buffer."
  ...
        (goto-char (point-min))
        (let* ((tags (vulpea-buffer-tags-get))
               (original-tags tags))
          (if (vulpea-project-p)
              (setq tags (cons "project" tags))
            (setq tags (remove "project" tags)))
...

Hey @d12frosted Would you consider updating the gist with this
https://gist.github.com/d12frosted/a60e8ccb9aceba031af243dff0d19b2e?permalink_comment_id=4976115#gistcomment-4976115
? Or give your opinion - last time I remember it was borking pdf files from opening in emacs 29.

Thanks.

@akashpal-21 Thanks, that makes sense. I had missed it as when I was looking at my agenda, the tasks wouldn't show up, but then I realised it was because I had customized the agenda view to only show tasks with deadlines in the current week. Changing the view to all tasks with todo did indeed show up the other tasks.

@akashpal-21 updated the gist. Thanks for reminder :)

Suppose there is a TODO item

* TODO Task
SCHEDULED: <2025-01-18 Sat>

When user presses </Enter/> on the org-time-stamp, the following function calls are done

  org-agenda-prepare("Day/Week")
  org-agenda-list(nil 739270 1)
  org-follow-timestamp-link()
  org-open-at-point(nil)

However; vulpea-agenda-files-update is not run before. Therefore user will see no TODO in the agenda buffer, unless the said function has been already run somehow before (for example by calling org-agenda)

Therefore, perhaps org-agenda-list should be advised to set the org-agenda-files variable too.

(advice-add 'org-agenda-list :before #'vulpea-agenda-files-update)

Thank you.

@akashpal-21 good point. I don't use org-agenda-list, so probably that's why didn't run into the issue.

I used the above code for years, tweaking it every so often to suit my use cases, and adapting some of the code from vulpea, to reduce dependencies. However, I've recently moved to org-mem, which now allows me to simply write this (copied from org-mem's README):

 (defun my-set-agenda-files (&rest _)
  (setq org-agenda-files
        (cl-loop
         for file in (org-mem-all-files)
         unless (string-search "archive" file)
         when (seq-find (lambda (entry)
                          (or (org-mem-entry-active-timestamps entry)
                              (org-mem-entry-todo-state entry)
                              (org-mem-entry-scheduled entry)
                              (org-mem-entry-deadline entry)))
                        (org-mem-entries-in file))
         collect file)))
(add-hook 'org-mem-post-full-scan-functions #'my-set-agenda-files)

The command is virtually instantaneous, across my thousands of org files. Hope this helps others that come across this.