# File activestorage/lib/active_storage/attached/one.rb, line 56
def attach(attachable)
  if record.persisted? && !record.changed?
    record.public_send("#{name}=", attachable)
    record.save
  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/jpeg")
person.avatar.attach(avatar_blob) # ActiveStorage::Blob object

# File activestorage/lib/active_storage/attached/one.rb, line 72
def attached?
  attachment.present?
end

Returns true if an attachment has been made.

class User < ApplicationRecord
  has_one_attached :avatar
end

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

# File activestorage/lib/active_storage/attached/one.rb, line 31
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 42
def blank?
  !attached?
end

Returns true if an attachment is not attached.

class User < ApplicationRecord
  has_one_attached :avatar
end

User.new.avatar.blank? # => true

# File activestorage/lib/active_storage/attached/one.rb, line 23
delegate :detach, to: :detach_one

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

# File activestorage/lib/active_storage/attached/one.rb, line 11
delegate :purge, to: :purge_one

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 17
delegate :purge_later, to: :purge_one

Purges the attachment through the queuing system.