1 files changed, 55 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/suppressor.rb b/activerecord/lib/active_record/suppressor.rb
new file mode 100644
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+++ b/activerecord/lib/active_record/suppressor.rb
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+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) # :nodoc:
+      SuppressorRegistry.suppressed[self.class.name] ? true : super
+    end
+  end
+
+  class SuppressorRegistry # :nodoc:
+    extend ActiveSupport::PerThreadRegistry
+
+    attr_reader :suppressed
+
+    def initialize
+      @suppressed = {}
+    end
+  end
+end