Where are you doing this? In the Rails app?
If so, then you can generate the URLs using upload.short_url and upload.url.
To find an upload record in the first place, you can do:
sha1 = Upload.sha1_from_long_url(...)
# or
sha1 = Upload.sha1_from_short_url(...)
# then
upload = Upload.find_by(sha1: sha1)