🎉 Add refcount-like functionality to storages.

This allows reuse of storage objects among different files.

backend/src/app/migrations/sql/0043-drop-old-tables-and-fields.sql

@@ -0,0 +1,10 @@
+DROP TABLE IF EXISTS file_media_thumbnail;
+
+ALTER TABLE profile DROP COLUMN photo;
+ALTER TABLE team DROP COLUMN photo;
+
+ALTER TABLE file_media_object DROP COLUMN path;
+ALTER TABLE file_media_object ALTER COLUMN media_id SET NOT NULL;
+
+ALTER TRIGGER media_object__insert__tgr
+   ON file_media_object RENAME TO file_media_object__on_insert__tgr;

backend/src/app/migrations/sql/0044-add-storage-refcount.sql

@@ -0,0 +1,26 @@
+ALTER TABLE storage_object
+  ADD COLUMN touched_at timestamptz NULL;
+
+CREATE INDEX storage_object__id_touched_at__idx
+    ON storage_object (touched_at, id)
+ WHERE touched_at IS NOT NULL;
+
+-- DROP TRIGGER file_media_object__on_delete__tgr ON file_media_object CASCADE;
+-- DROP FUNCTION on_delete_file_media_object () ;
+
+CREATE OR REPLACE FUNCTION on_delete_file_media_object()
+  RETURNS TRIGGER AS $func$
+  BEGIN
+    IF OLD.thumbnail_id IS NOT NULL THEN
+      UPDATE storage_object
+         SET touched_at = now()
+       WHERE id in (OLD.thumbnail_id, OLD.media_id);
+    ELSE
+      UPDATE storage_object
+         SET touched_at = now()
+       WHERE id = OLD.media_id;
+    END IF;
+    RETURN OLD;
+  END;
+$func$ LANGUAGE plpgsql;
+