Increase `AR#cache_key` precision to nanoseconds

activerecord/lib/active_record/integration.rb

@@ -39,7 +39,7 @@ def cache_key
       when new_record?
         "#{self.class.model_name.cache_key}/new"
       when timestamp = self[:updated_at]
-        timestamp = timestamp.utc.to_s(:number)
+        timestamp = timestamp.utc.to_s(:nsec)
         "#{self.class.model_name.cache_key}/#{id}-#{timestamp}"
       else
         "#{self.class.model_name.cache_key}/#{id}"

activerecord/test/cases/base_test.rb

@@ -1939,7 +1939,7 @@ def test_cache_key_for_existing_record_is_not_timezone_dependent
 
   def test_cache_key_format_for_existing_record_with_updated_at
     dev = Developer.first
-    assert_equal "developers/#{dev.id}-#{dev.updated_at.utc.to_s(:number)}", dev.cache_key
+    assert_equal "developers/#{dev.id}-#{dev.updated_at.utc.to_s(:nsec)}", dev.cache_key
   end
 
   def test_cache_key_format_for_existing_record_with_nil_updated_at

activesupport/lib/active_support/core_ext/time/conversions.rb

@@ -5,6 +5,7 @@ class Time
   DATE_FORMATS = {
     :db           => '%Y-%m-%d %H:%M:%S',
     :number       => '%Y%m%d%H%M%S',
+    :nsec         => '%Y%m%d%H%M%S%9N',
     :time         => '%H:%M',
     :short        => '%d %b %H:%M',
     :long         => '%B %d, %Y %H:%M',

activesupport/test/core_ext/time_ext_test.rb

@@ -557,12 +557,14 @@ def test_next_week_near_daylight_end
   end
 
   def test_to_s
-    time = Time.utc(2005, 2, 21, 17, 44, 30)
+    time = Time.utc(2005, 2, 21, 17, 44, 30.12345678901)
     assert_equal time.to_default_s,                 time.to_s
     assert_equal time.to_default_s,                 time.to_s(:doesnt_exist)
     assert_equal "2005-02-21 17:44:30",             time.to_s(:db)
     assert_equal "21 Feb 17:44",                    time.to_s(:short)
     assert_equal "17:44",                           time.to_s(:time)
+    assert_equal "20050221174430",                  time.to_s(:number)
+    assert_equal "20050221174430123456789",         time.to_s(:nsec)
     assert_equal "February 21, 2005 17:44",         time.to_s(:long)
     assert_equal "February 21st, 2005 17:44",       time.to_s(:long_ordinal)
     with_env_tz "UTC" do