Don't load has_one associations during autosave

If the association has been accessed but is not currently loaded, there
can't be any changes to save. This was previously fixed for belongs_to
associations in a94fe29.

Author: eugeneius

activerecord/lib/active_record/autosave_association.rb

@@ -433,7 +433,9 @@ def save_collection_association(reflection)
       # ActiveRecord::Base after the AutosaveAssociation module, which it does by default.
       def save_has_one_association(reflection)
         association = association_instance_get(reflection.name)
-        record      = association && association.load_target
+        return unless association && association.loaded?
+
+        record = association.load_target
         return unless record && !record.destroyed?
 
         autosave = reflection.options[:autosave]

activerecord/test/cases/autosave_association_test.rb

@@ -285,6 +285,12 @@ def test_not_resaved_when_unchanged
     assert_queries_count(4) { firm.save! }
   end
 
+  def test_should_not_load_the_associated_model
+    firm = companies(:first_firm)
+    firm.reset_unvalidated_account
+    assert_no_queries { firm.save! }
+  end
+
   def test_callbacks_firing_order_on_create
     eye = Eye.create(iris_attributes: { color: "honey" })
     assert_equal [true, false], eye.after_create_callbacks_stack
@@ -562,6 +568,12 @@ def test_validation_does_not_validate_non_dirty_association_target
       Cpk::Order.create!(id: [1, 2], book: Cpk::Book.new(title: "Book", id: [3, 4]))
     end
   end
+
+  def test_should_not_load_the_associated_model
+    tagging = taggings(:welcome_general)
+    tagging.reset_tag
+    assert_no_queries { tagging.save! }
+  end
 end
 
 class TestDefaultAutosaveAssociationOnAHasManyAssociationWithAcceptsNestedAttributes < ActiveRecord::TestCase
@@ -1048,6 +1060,12 @@ def test_replace_on_duplicated_object
     assert_equal 2, firm.clients.length
     assert_includes firm.clients, Client.find_by_name("New Client")
   end
+
+  def test_should_not_load_the_associated_model
+    firm = companies(:first_firm)
+    firm.clients.reset
+    assert_no_queries { firm.save! }
+  end
 end
 
 class TestDefaultAutosaveAssociationOnNewRecord < ActiveRecord::TestCase