t/var/configs/extra.json

   1 {
   2         "sets": [{
   3                 "class": "Photo",
   4                 "quantity": "all",
   5         "external": {
   6             "file": {
   7                 "class": "File",
   8                 "args": {"path":"__ATTR(photo_dir)__"}
   9             }
  10         }
  11         }]
  12 }