Merge pull request #7377 from brainopia/use_inversed_parent_for_first_and_last_child

Use inversed parent for first and last child of has_many association

[Backport] Closes #3223.

Conflicts:
	activerecord/lib/active_record/associations/collection_association.rb

activerecord/CHANGELOG.md

 ## Rails 3.2.9 (unreleased)
 
+*   Use inversed parent for first and last child of has_many association.
+
+    *Ravil Bayramgalin*
+
 *   Fix Column.microseconds and Column.fast_string_to_date to avoid converting
     timestamp seconds to a float, since it occasionally results in inaccuracies
     with microsecond-precision times. Fixes #7352.

activerecord/lib/active_record/associations/collection_association.rb

@@ -569,7 +569,7 @@ def first_or_last(type, *args)
           args.shift if args.first.is_a?(Hash) && args.first.empty?
 
           collection = fetch_first_or_last_using_find?(args) ? scoped : load_target
-          collection.send(type, *args)
+          collection.send(type, *args).tap {|it| set_inverse_instance it }
         end
     end
   end

activerecord/test/cases/associations/inverse_associations_test.rb

@@ -259,6 +259,12 @@ def test_parent_instance_should_be_shared_with_replaced_via_accessor_children
     assert_equal m.name, i.man.name, "Name of man should be the same after changes to replaced-child-owned instance"
   end
 
+  def test_parent_instance_should_be_shared_with_first_and_last_child
+    man = Man.first
+    assert man.interests.first.man.equal? man
+    assert man.interests.last.man.equal? man
+  end
+
   def test_trying_to_use_inverses_that_dont_exist_should_raise_an_error
     assert_raise(ActiveRecord::InverseOfAssociationNotFoundError) { Man.find(:first).secret_interests }
   end