Rails Suppressor Pattern

While grokking through Rails source code, one pattern caught my eye, namely Suppressor.

Here is the full listing, and as you could spot, it’s quite concise.

But, I spent some time trying to figure out how it works in the context of ActiveRecord. How does it suppress callbacks and notifications?

Honestly, it took me a while to figure out. Give yourselve several minutes to read through the code. It’s really there!

module ActiveRecord
  module Suppressor
    extend ActiveSupport::Concern

    class << self
      def registry # :nodoc:
        ActiveSupport::IsolatedExecutionState[:active_record_suppressor_registry] ||= {}
      end
    end

    module ClassMethods
      def suppress(&block)
        previous_state = Suppressor.registry[name]
        Suppressor.registry[name] = true
        yield
      ensure
        Suppressor.registry[name] = previous_state
      end
    end

    def save(**) # :nodoc:
      Suppressor.registry[self.class.name] ? true : super
    end

    def save!(**) # :nodoc:
      Suppressor.registry[self.class.name] ? true : super
    end
  end
end

How smart! I thought after discovery.

Turns out, when this class is included in ActiveRecord, it replaces save method of the instance with this implementation from above, that either returns true and skips the execution or calls super method, which, I’m sure, should be available in the execution stack.

Inspired by this I was able to quickly implement the same idea in my code, responsible for suppression of the Notifications delivery class, which was just PORO.

Final thouhts, how often we ignore wisdom of others lying right under the feets? Just read the beautiful code we all already have!