path: root/activerecord/lib/active_record/suppressor.rb

module ActiveRecord
  # ActiveRecord::Suppressor prevents the receiver from being saved during
  # a given block.
  #
  # For example, here's a pattern of creating notifications when new comments
  # are posted. (The notification may in turn trigger an email, a push
  # notification, or just appear in the UI somewhere):
  # 
  # class Comment < ActiveRecord::Base
  #   belongs_to :commentable, polymorphic: true
  #   after_create -> { Notification.create! comment: self,
  #     recipients: commentable.recipients }
  # end
  # 
  # That's what you want the bulk of the time. New comment creates a new
  # Notification. But there may well be off cases, like copying a commentable
  # and its comments, where you don't want that. So you'd have a concern
  # something like this:
  # 
  # module Copyable
  #   def copy_to(destination)
  #     Notification.suppress do
  #       # Copy logic that creates new comments that we do not want
  #       # triggering notifications.
  #     end
  #   end
  # end
  module Suppressor
    extend ActiveSupport::Concern

    module ClassMethods
      def suppress(&block)
        SuppressorRegistry.suppressed[name] = true
        yield
      ensure
        SuppressorRegistry.suppressed[name] = false
      end
    end

    # Ignore saving events if we're in suppression mode.
    def save!(*args)
      SuppressorRegistry.suppressed[self.class.name] ? self : super
    end
  end

  class SuppressorRegistry # :nodoc:
    extend ActiveSupport::PerThreadRegistry

    attr_reader :suppressed

    def initialize
      @suppressed = {}
    end
  end
end