fixes #21815

The default timestamp used for AR is `updated_at` in nanoseconds! (:nsec) This causes issues on any machine that runs an OS that supports nanoseconds timestamps, i.e. not-OS X, where the cache_key of the record persisted in the database (milliseconds precision) is out-of-sync with the cache_key in the ruby VM.

This commit adds:

A test that shows the issue, it can be found in the separate file `cache_key_test.rb`, because
- model couldn't be defined inline
- transactional testing needed to be turned off to get it to pass the MySQL tests
This seemed cleaner than putting it in an existing testcase file.

It adds :usec as a dateformat that calculates datetime in microseconds

It sets precision of cache_key to :usec instead of :nsec, as no db supports nsec precision on timestamps

1 files changed, 1 insertions, 0 deletions

diff --git a/activesupport/test/core_ext/time_ext_test.rb b/activesupport/test/core_ext/time_ext_test.rb
index b14c04fba6..2d0fb70a6b 100644
--- a/activesupport/test/core_ext/time_ext_test.rb
+++ b/activesupport/test/core_ext/time_ext_test.rb
@@ -534,6 +534,7 @@ class TimeExtCalculationsTest < ActiveSupport::TestCase
     assert_equal "17:44",                           time.to_s(:time)
     assert_equal "20050221174430",                  time.to_s(:number)
     assert_equal "20050221174430123456789",         time.to_s(:nsec)
+    assert_equal "20050221174430123456",            time.to_s(:usec)
     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