Merge pull request rails#12443 from arthurnn/add_inverse_of_add_target

Add inverse of add target

activerecord/lib/active_record/associations/collection_association.rb

@@ -350,6 +350,7 @@ def add_to_target(record)
         end
 
         callback(:after_add, record)
+        set_inverse_instance(record)
 
         record
       end

activerecord/test/cases/associations/inverse_associations_test.rb

@@ -290,6 +290,19 @@ def test_parent_instance_should_be_shared_with_first_n_and_last_n_children
   def test_trying_to_use_inverses_that_dont_exist_should_raise_an_error
     assert_raise(ActiveRecord::InverseOfAssociationNotFoundError) { Man.find(:first).secret_interests }
   end
+
+  def test_child_instance_should_point_to_parent_without_saving
+    man = Man.new
+    i = Interest.create(:topic => 'Industrial Revolution Re-enactment')
+
+    man.interests << i
+    assert_not_nil i.man
+
+    i.man.name = "Charles"
+    assert_equal i.man.name, man.name
+
+    assert !man.persisted?
+  end
 end
 
 class InverseBelongsToTests < ActiveRecord::TestCase