Use _read_attribute when autosaving has_one associations

activerecord/lib/active_record/autosave_association.rb

@@ -453,7 +453,7 @@ def save_has_one_association(reflection)
           if autosave && record.marked_for_destruction?
             record.destroy
           elsif autosave != false
-            key = reflection.options[:primary_key] ? public_send(reflection.options[:primary_key]) : id
+            key = reflection.options[:primary_key] ? _read_attribute(reflection.options[:primary_key].to_s) : id
 
             if (autosave && record.changed_for_autosave?) || _record_changed?(reflection, record, key)
               unless reflection.through_reflection

activerecord/test/cases/autosave_association_test.rb

@@ -798,6 +798,13 @@ def test_assign_ids_with_cpk_for_two_models
     assert_includes order.books, cpk_books(:cpk_great_author_second_book)
   end
 
+  def test_has_one_cpk_has_one_autosave_with_id
+    book = Cpk::Book.create!(author_id: 1, number: 3, shop_id: 2)
+    order = Cpk::OrderWithPrimaryKeyAssociatedBook.create!(book: book, shop_id: 2)
+
+    assert_equal(book.order.id, order.id)
+  end
+
   def test_assign_ids_for_through_a_belongs_to
     firm = Firm.new("name" => "Apple")
     firm.developer_ids = [developers(:david).id, developers(:jamis).id]

activerecord/test/models/cpk/order.rb

@@ -16,4 +16,8 @@ class BrokenOrder < Order
     has_many :books
     has_one :book
   end
+
+  class OrderWithPrimaryKeyAssociatedBook < Order
+    has_one :book, primary_key: :id, foreign_key: :order_id
+  end
 end