class ActiveStorage::Attached::One

person.avatar.attach(avatar_blob) # ActiveStorage::Blob object
person.avatar.attach(io: File.open("/path/to/face.jpg"), filename: "face.jpg", content_type: "image/jpeg")
person.avatar.attach(params[:signed_blob_id]) # Signed reference to blob from direct upload
person.avatar.attach(params[:avatar]) # ActionDispatch::Http::UploadedFile object

record is next saved.
the database immediately. Otherwise, it'll be saved to the DB when the
If the record is persisted and unchanged, the attachment is saved to

Attaches an +attachable+ to the record.

def attach(attachable)
  record.public_send("#{name}=", attachable)
  if record.persisted? && !record.changed?
    return if !record.save
  end
  record.public_send("#{name}")
end