Add DateTime#subsec

Mirrors the Time#subsec method by returning the fraction
of the second as a Rational.

3 files changed, 16 insertions, 0 deletions

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 304b540aa2..8908247287 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Add `DateTime#subsec` to return the fraction of a second as a `Rational`.
+
+    *Andrew White*
+
 *   Add additional aliases for `DateTime#utc` to mirror the ones on
     `ActiveSupport::TimeWithZone` and `Time`.
 
diff --git a/activesupport/lib/active_support/core_ext/date_time/calculations.rb b/activesupport/lib/active_support/core_ext/date_time/calculations.rb
index 1eaf51243c..7e214524df 100644
--- a/activesupport/lib/active_support/core_ext/date_time/calculations.rb
+++ b/activesupport/lib/active_support/core_ext/date_time/calculations.rb
@@ -28,6 +28,13 @@ class DateTime
     end_of_day.to_i - to_i
   end
 
+  # Returns the fraction of a second as a +Rational+
+  #
+  #   DateTime.new(2012, 8, 29, 0, 0, 0.5).subsec # => (1/2)
+  def subsec
+    sec_fraction
+  end
+
   # Returns a new DateTime where one or more of the elements have been changed
   # according to the +options+ parameter. The time options (<tt>:hour</tt>,
   # <tt>:min</tt>, <tt>:sec</tt>) reset cascadingly, so if only the hour is
diff --git a/activesupport/test/core_ext/date_time_ext_test.rb b/activesupport/test/core_ext/date_time_ext_test.rb
index d57e71df3b..c19992553f 100644
--- a/activesupport/test/core_ext/date_time_ext_test.rb
+++ b/activesupport/test/core_ext/date_time_ext_test.rb
@@ -400,4 +400,9 @@ class DateTimeExtCalculationsTest < ActiveSupport::TestCase
     assert_equal 0, DateTime.civil(2000).nsec
     assert_equal 500000000, DateTime.civil(2000, 1, 1, 0, 0, Rational(1,2)).nsec
   end
+
+  def test_subsec
+    assert_equal 0, DateTime.civil(2000).subsec
+    assert_equal Rational(1,2), DateTime.civil(2000, 1, 1, 0, 0, Rational(1,2)).subsec
+  end
 end