class ActiveStorage::Attached::Many

document.images.attach([ first_blob, second_blob ])
document.images.attach(io: File.open("/path/to/racecar.jpg"), filename: "racecar.jpg", content_type: "image/jpeg")
document.images.attach(params[:signed_blob_id]) # Signed reference to blob from direct upload
document.images.attach(params[:images]) # Array of ActionDispatch::Http::UploadedFile objects

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

Attaches one or more +attachables+ to the record.

def attach(*attachables)
  if record.persisted? && !record.changed?
    record.public_send("#{name}=", blobs + attachables.flatten)
    record.save
  else
    record.public_send("#{name}=", (change&.attachables || blobs) + attachables.flatten)
  end
end