# File activestorage/lib/active_storage/attached/one.rb, line 30
def attach(attachable)
  if record.persisted? && !record.changed?
    record.update(name => attachable)
  else
    record.public_send("#{name}=", attachable)
  end
end

Attaches an attachable to the record.

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

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

# File activestorage/lib/active_storage/attached/one.rb, line 45
def attached?
  attachment.present?
end

Returns true if an attachment has been made.

class User < ActiveRecord::Base
  has_one_attached :avatar
end

User.new.avatar.attached? # => false

# File activestorage/lib/active_storage/attached/one.rb, line 12
def attachment
  change.present? ? change.attachment : record.public_send("#{name}_attachment")
end

Returns the associated attachment record.

You don't have to call this method to access the attachment's methods as they are all available at the model level.

# File activestorage/lib/active_storage/attached/one.rb, line 50
def detach
  if attached?
    attachment.delete
    write_attachment nil
  end
end

Deletes the attachment without purging it, leaving its blob in place.

# File activestorage/lib/active_storage/attached/one.rb, line 59
def purge
  if attached?
    attachment.purge
    write_attachment nil
  end
end

Directly purges the attachment (i.e. destroys the blob and attachment and deletes the file on the service).

# File activestorage/lib/active_storage/attached/one.rb, line 67
def purge_later
  if attached?
    attachment.purge_later
    write_attachment nil
  end
end

Purges the attachment through the queuing system.