docs: def set_location(self, uri, size, checksum, storage_class=None):
          """Set only URI location of for object.
  
          Useful to link files on externally controlled storage. If a file
          instance has already been set, this methods raises an
          ``FileInstanceAlreadySetError`` exception.
  
          :param uri: Full URI to object (which can be interpreted by the storage
              interface).
          :param size: Size of file.
          :param checksum: Checksum of file.
          :param storage_class: Storage class where file is stored ()
          """
          self.file = FileInstance()
          self.file.set_uri(
              uri, size, checksum, storage_class=storage_class
          )
          db.session.add(self.file)
          return self