Merge branch 'master' into adequaterecord

* master: (108 commits)
  make tests pass on Ruby 2.2
  Use Sqlite3 adapter in examples
  use the body proxy to freeze headers
  just ask the response for the commit status, we do not need to ask the jar
  only write the jar if the response isn't committed
  Fix a grammatical error in the i18n guide [ci skip]
  use method_defined? to check whether or not a method is defined
  Enhance docs for update_attribute [ci-skip]
  Change usec to 0 on tests that compare seconds
  Unit test for mysql quote time usec
  Changelog entry for mysql56 microseconds
  Test microsecond on mysql 5.6
  MySQL 5.6 and later supports microsecond precision in datetime.
  [ci skip] Add documentation for original_fullpath.
  Remove mocking on save, when not necessary
  comment why we are modifying global state. [ci skip]
  `change_table` supports `citext`. Follow up to #12523.
  Removed unnecessary command "application"
  register OID for PostgreSQL citex datatype [Troy Kruthoff & Lachlan Sylvester]
  Fixes STI when 2+ levels deep.
  ...

1 files changed, 1 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/associations/preloader/through_association.rb b/activerecord/lib/active_record/associations/preloader/through_association.rb
index 2a8530af62..70e97432e4 100644
--- a/activerecord/lib/active_record/associations/preloader/through_association.rb
+++ b/activerecord/lib/active_record/associations/preloader/through_association.rb
@@ -23,7 +23,7 @@ module ActiveRecord
 
           reset_association owners, through_reflection.name
 
-          middle_records = through_records.map { |(_,rec)| rec }.flatten
+          middle_records = through_records.flat_map { |(_,rec)| rec }
 
           preloaders = preloader.preload(middle_records,
                                          source_reflection.name,