Merge pull request #6986 from kennyj/fix_6975

Fix #6975. Round usec when writing timestamp attribute.

Conflicts:
	activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb

3 files changed, 34 insertions, 5 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 9c063e897c..6f81625429 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,5 +1,10 @@
 ## Rails 3.2.9 (unreleased)
 
+*   Round usec when comparing timestamp attributes in the dirty tracking.
+    Fixes #6975.
+
+    *kennyj*
+
 *   Use inversed parent for first and last child of has_many association.
 
     *Ravil Bayramgalin*
diff --git a/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb b/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
index 7abe29c7d5..4c3d5eed4c 100644
--- a/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
+++ b/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
@@ -41,11 +41,14 @@ module ActiveRecord
                   unless time.acts_like?(:time)
                     time = time.is_a?(String) ? Time.zone.parse(time) : time.to_time rescue 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
+                  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
                 end
               EOV
               generated_attribute_methods.module_eval(method_body, __FILE__, line)
@@ -59,6 +62,12 @@ module ActiveRecord
             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
diff --git a/activerecord/test/cases/dirty_test.rb b/activerecord/test/cases/dirty_test.rb
index 26afd203d2..3bd2e909d7 100644
--- a/activerecord/test/cases/dirty_test.rb
+++ b/activerecord/test/cases/dirty_test.rb
@@ -521,6 +521,21 @@ class DirtyTest < ActiveRecord::TestCase
     assert !pirate.previous_changes.key?('created_on')
   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?