Don't autosave unchanged has_one through records

activerecord/CHANGELOG.md

+*   Don't autosave unchanged has_one through records
+
+    *Alan Kennedy*, *Steve Parrington*
+
 *   When a thread is killed, rollback the active transaction, instead of
     committing it during the stack unwind. Previously, we could commit half-
     completed work. This fix only works for Ruby 2.0+; on 1.9, we can't

activerecord/lib/active_record/autosave_association.rb

@@ -403,7 +403,9 @@ def save_has_one_association(reflection)
 
       # If the record is new or it has changed, returns true.
       def record_changed?(reflection, record, key)
-        record.new_record? || record[reflection.foreign_key] != key || record.attribute_changed?(reflection.foreign_key)
+        record.new_record? ||
+          (record.attributes.keys.include?(reflection.foreign_key) && record[reflection.foreign_key] != key) ||
+          record.attribute_changed?(reflection.foreign_key)
       end
 
       # Saves the associated record if it's new or <tt>:autosave</tt> is enabled.

activerecord/test/cases/autosave_association_test.rb

@@ -19,6 +19,9 @@
 require 'models/eye'
 require 'models/electron'
 require 'models/molecule'
+require 'models/member'
+require 'models/member_detail'
+require 'models/organization'
 
 class TestAutosaveAssociationsInGeneral < ActiveRecord::TestCase
   def test_autosave_validation
@@ -1116,6 +1119,27 @@ def test_should_not_load_the_associated_model
   end
 end
 
+class TestAutosaveAssociationOnAHasOneThroughAssociation < ActiveRecord::TestCase
+  self.use_transactional_fixtures = false unless supports_savepoints?
+
+  def setup
+    super
+    organization = Organization.create
+    @member = Member.create
+    MemberDetail.create(organization: organization, member: @member)
+  end
+
+  def test_should_not_has_one_through_model
+    class << @member.organization
+      def save(*args)
+        super
+        raise 'Oh noes!'
+      end
+    end
+    assert_nothing_raised { @member.save }
+  end
+end
+
 class TestAutosaveAssociationOnABelongsToAssociation < ActiveRecord::TestCase
   self.use_transactional_fixtures = false unless supports_savepoints?