Revert "Merge pull request #6986 from kennyj/fix_6975"

This reverts commit 8905c1f.

Closes #8460

Conflicts:
	activerecord/test/cases/dirty_test.rb

activerecord/CHANGELOG.md

@@ -1,5 +1,10 @@
 ## Rails 3.2.12 (unreleased) ##
 
+*   Revert round usec when comparing timestamp attributes in the dirty tracking.
+    Fixes #8460.
+
+    *Andrew White*
+
 *   Revert creation of through association models when using `collection=[]`
     on a `has_many :through` association from an unsaved model.
     Fix #7661, #8269.

activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb

@@ -42,14 +42,11 @@ def #{attr_name}=(original_time)
                   unless time.acts_like?(:time)
                     time = time.is_a?(String) ? Time.zone.parse(time) : time.to_time rescue time
                   end
-                  zoned_time   = time && time.in_time_zone rescue nil
-                  rounded_time = round_usec(zoned_time)
-                  rounded_value = round_usec(read_attribute("#{attr_name}"))
-                  if (rounded_value != rounded_time) || (!rounded_value && original_time)
-                    write_attribute("#{attr_name}", original_time)
-                    #{attr_name}_will_change!
-                    @attributes_cache["#{attr_name}"] = zoned_time
-                  end
+                  time = time.in_time_zone rescue nil if time
+                  changed = read_attribute(:#{attr_name}) != time
+                  write_attribute(:#{attr_name}, original_time)
+                  #{attr_name}_will_change! if changed
+                  @attributes_cache["#{attr_name}"] = time
                 end
               EOV
               generated_attribute_methods.module_eval(method_body, __FILE__, line)
@@ -63,12 +60,6 @@ def create_time_zone_conversion_attribute?(name, column)
             time_zone_aware_attributes && !self.skip_time_zone_conversion_for_attributes.include?(name.to_sym) && column.type.in?([:datetime, :timestamp])
           end
       end
-
-      private
-      def round_usec(value)
-        return unless value
-        value.change(:usec => 0)
-      end
     end
   end
 end

activerecord/test/cases/dirty_test.rb

@@ -563,21 +563,6 @@ def test_datetime_attribute_can_be_updated_with_fractional_seconds
     end
   end
 
-  def test_setting_time_attributes_with_time_zone_field_to_same_time_should_not_be_marked_as_a_change
-    in_time_zone 'Paris' do
-      target = Class.new(ActiveRecord::Base)
-      target.table_name = 'pirates'
-
-      created_on = Time.now
-
-      pirate = target.create(:created_on => created_on)
-      pirate.reload # Here mysql truncate the usec value to 0
-
-      pirate.created_on = created_on
-      assert !pirate.created_on_changed?
-    end
-  end
-
   private
     def with_partial_updates(klass, on = true)
       old = klass.partial_updates?