add #no_touching on ActiveRecord models

activerecord/CHANGELOG.md

+*   Added `ActiveRecord::Base.no_touching`, which allows ignoring touch on models.
+
+    Examples:
+
+      Post.no_touching do
+        Post.first.touch
+      end
+
+    *Sam Stephenson*, *Damien Mathieu*
+
 *   Prevent the counter cache from being decremented twice when destroying
     a record on a has_many :through association.
 

activerecord/lib/active_record.rb

@@ -45,6 +45,7 @@ module ActiveRecord
   autoload :Migrator, 'active_record/migration'
   autoload :ModelSchema
   autoload :NestedAttributes
+  autoload :NoTouching
   autoload :Persistence
   autoload :QueryCache
   autoload :Querying

activerecord/lib/active_record/base.rb

@@ -295,6 +295,7 @@ class Base
     extend Delegation::DelegateCache
 
     include Persistence
+    include NoTouching
     include ReadonlyAttributes
     include ModelSchema
     include Inheritance

activerecord/lib/active_record/no_touching.rb

+module ActiveRecord
+  # = Active Record No Touching
+  module NoTouching
+    extend ActiveSupport::Concern
+
+    module ClassMethods
+      # Lets you selectively disable calls to `touch` for the
+      # duration of a block.
+      #
+      # ==== Examples
+      #   ActiveRecord::Base.no_touching do
+      #     Project.first.touch  # does nothing
+      #     Message.first.touch  # does nothing
+      #   end
+      #
+      #   Project.no_touching do
+      #     Project.first.touch  # does nothing
+      #     Message.first.touch  # works, but does not touch the associated project
+      #   end
+      #
+      def no_touching(&block)
+        NoTouching.apply_to(self, &block)
+      end
+    end
+
+    class << self
+      def apply_to(klass) #:nodoc:
+        klasses.push(klass)
+        yield
+      ensure
+        klasses.pop
+      end
+
+      def applied_to?(klass) #:nodoc:
+        klasses.any? { |k| k >= klass }
+      end
+
+      private
+        def klasses
+          Thread.current[:no_touching_classes] ||= []
+        end
+    end
+
+    def no_touching?
+      NoTouching.applied_to?(self.class)
+    end
+
+    def touch(*)
+      super unless no_touching?
+    end
+  end
+end

activerecord/test/cases/timestamp_test.rb

@@ -11,6 +11,7 @@ class TimestampTest < ActiveRecord::TestCase
 
   def setup
     @developer = Developer.first
+    @owner = Owner.first
     @developer.update_columns(updated_at: Time.now.prev_month)
     @previously_updated_at = @developer.updated_at
   end
@@ -92,6 +93,53 @@ def test_touching_a_record_without_timestamps_is_unexceptional
     assert_nothing_raised { Car.first.touch }
   end
 
+  def test_touching_a_no_touching_object
+    Developer.no_touching do
+      assert @developer.no_touching?
+      assert !@owner.no_touching?
+      @developer.touch
+    end
+
+    assert !@developer.no_touching?
+    assert !@owner.no_touching?
+    assert_equal @previously_updated_at, @developer.updated_at
+  end
+
+  def test_touching_related_objects
+    @owner = Owner.first
+    @previously_updated_at = @owner.updated_at
+
+    Owner.no_touching do
+      @owner.pets.first.touch
+    end
+
+    assert_equal @previously_updated_at, @owner.updated_at
+  end
+
+  def test_global_no_touching
+    ActiveRecord::Base.no_touching do
+      assert @developer.no_touching?
+      assert @owner.no_touching?
+      @developer.touch
+    end
+
+    assert !@developer.no_touching?
+    assert !@owner.no_touching?
+    assert_equal @previously_updated_at, @developer.updated_at
+  end
+
+  def test_no_touching_threadsafe
+    Thread.new do
+      Developer.no_touching do
+        assert @developer.no_touching?
+
+        sleep(1)
+      end
+    end
+
+    assert !@developer.no_touching?
+  end
+
   def test_saving_a_record_with_a_belongs_to_that_specifies_touching_the_parent_should_update_the_parent_updated_at
     pet   = Pet.first
     owner = pet.owner