3 files changed, 57 insertions, 0 deletions
diff --git a/activerecord/lib/active_record.rb b/activerecord/lib/active_record.rb
index d9d47c3d99..ef14e065ae 100644
--- a/activerecord/lib/active_record.rb
+++ b/activerecord/lib/active_record.rb
@@ -62,6 +62,7 @@ module ActiveRecord
   autoload :Serialization
   autoload :StatementCache
   autoload :Store
+  autoload :Suppressor
   autoload :TableMetadata
   autoload :Timestamp
   autoload :Transactions
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 100d3780f6..cc03e37a12 100644
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -313,6 +313,7 @@ module ActiveRecord #:nodoc:
     include Serialization
     include Store
     include SecureToken
+    include Suppressor
   end
 
   ActiveSupport.run_load_hooks(:active_record, Base)
diff --git a/activerecord/lib/active_record/suppressor.rb b/activerecord/lib/active_record/suppressor.rb
new file mode 100644
index 0000000000..b47f02143c
--- /dev/null
+++ b/activerecord/lib/active_record/suppressor.rb
@@ -0,0 +1,55 @@
+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