(feat): graph of bfs from given node (#418)

org-roam-db.el

@@ -263,6 +263,32 @@ If the file does not have any connections, nil is returned."
          (files (mapcar 'car-safe (emacsql (org-roam-db) query file))))
     files))
 
+(defun org-roam-db--links-with-max-distance (file max-distance)
+  "Return all files reachable from/connected to FILE in at most MAX-DISTANCE steps,
+including the file itself.  If the file does not have any connections, nil is returned."
+  (let* ((query "WITH RECURSIVE
+                   links_of(file, link) AS
+                     (SELECT \"from\", \"to\" FROM links UNION
+                      SELECT \"to\", \"from\" FROM links),
+                   -- Links are traversed in a breadth-first search.  In order to calculate the
+                   -- distance of nodes and to avoid following cyclic links, the visited nodes
+                   -- are tracked in 'trace'.
+                   connected_component(file, trace) AS
+                     (VALUES($s1, json_array($s1))
+                      UNION
+                      SELECT lo.link, json_insert(cc.trace, '$[' || json_array_length(cc.trace) || ']', lo.link) FROM
+                      connected_component AS cc JOIN links_of AS lo USING(file)
+                      WHERE (
+                        -- Avoid cycles by only visiting each file once.
+                        (SELECT count(*) FROM json_each(cc.trace) WHERE json_each.value == lo.link) == 0
+                        -- Note: BFS is cut off early here.
+                        AND json_array_length(cc.trace) < ($s2 + 1)))
+                   SELECT DISTINCT file, min(json_array_length(trace)) AS distance
+                   FROM connected_component GROUP BY file ORDER BY distance;")
+         ;; In principle the distance would be available in the second column.
+         (files (mapcar 'car-safe (emacsql (org-roam-db) query file max-distance))))
+    files))
+
 ;;;;; Updating
 (defun org-roam-db--update-titles ()
   "Update the title of the current buffer into the cache."

org-roam-graph.el

@@ -130,7 +130,7 @@ into a digraph."
     (let* ((nodes (org-roam-db-query node-query))
            (edges-query
             `[:with selected :as [:select [file] :from ,node-query]
-              :select [to from] :from links
+              :select :distinct [to from] :from links
               :where (and (in to selected) (in from selected))])
            (edges (org-roam-db-query edges-query)))
       (insert "digraph \"org-roam\" {\n")
@@ -186,18 +186,22 @@ If PREFIX, then the graph is generated but the viewer is not invoked."
 	        (call-process org-roam-graph-viewer nil 0 nil temp-graph)
         (view-file temp-graph)))))
 
-(defun org-roam-graph-show-connected-component (&optional prefix)
+(defun org-roam-graph-show-connected-component (&optional max-distance no-display)
   "Like `org-roam-graph-show', but only show nodes connected to the current entry.
-If PREFIX is non-nil, the graph is generated but the viewer is not invoked."
+If MAX-DISTANCE is non-nil, only nodes within the given number of steps are shown.
+If NO-DISPLAY is non-nil, the graph is generated but the viewer is not invoked."
   (interactive "P")
   (unless (org-roam--org-roam-file-p)
     (user-error "Not in an Org-roam file"))
   (let* ((file (file-truename (buffer-file-name)))
-         (files (or (org-roam-db--connected-component file) (list file)))
+         (files (or (if (and max-distance (>= (prefix-numeric-value max-distance) 0))
+                        (org-roam-db--links-with-max-distance file max-distance)
+                      (org-roam-db--connected-component file))
+                    (list file)))
          (query `[:select [file titles]
                   :from titles
                   :where (in file [,@files])]))
-    (org-roam-graph-show prefix query)))
+    (org-roam-graph-show no-display query)))
 
 (provide 'org-roam-graph)