Attachments associate records with blobs. Usually that's a one record-many blobs relationship, but it is possible to associate many different records with the same blob. If you're doing that, you'll want to declare with has_one/many_attached :thingy, dependent: false, so that destroying any one record won't destroy the blob as well. (Then you'll need to do your own garbage collecting, though).

Methods
P
Instance Public methods
purge()

Synchronously purges the blob (deletes it from the configured service) and destroys the attachment.

Source: show | on GitHub 

# File activestorage/app/models/active_storage/attachment.rb, line 20
def purge
  destroy
  blob.purge
end
purge_later()

Destroys the attachment and asynchronously purges the blob (deletes it from the configured service).

Source: show | on GitHub 

# File activestorage/app/models/active_storage/attachment.rb, line 26
def purge_later
  destroy
  blob.purge_later
end