[Fix 52791] Revert "Remove ActiveRecord::AttributeAssignment#assign_nested_parameter_attributes"

This reverts commit ded026b.

This broke existing behavior that allowed a has_one to be updated when a
new record was being created.

Author: jimnanney

activerecord/lib/active_record/attribute_assignment.rb

@@ -4,21 +4,29 @@ module ActiveRecord
   module AttributeAssignment
     private
       def _assign_attributes(attributes)
-        multi_parameter_attributes = nil
+        multi_parameter_attributes = nested_parameter_attributes = nil
 
         attributes.each do |k, v|
           key = k.to_s
 
           if key.include?("(")
             (multi_parameter_attributes ||= {})[key] = v
+          elsif v.is_a?(Hash)
+            (nested_parameter_attributes ||= {})[key] = v
           else
             _assign_attribute(key, v)
           end
         end
 
+        assign_nested_parameter_attributes(nested_parameter_attributes) if nested_parameter_attributes
         assign_multiparameter_attributes(multi_parameter_attributes) if multi_parameter_attributes
       end
 
+      # Assign any deferred nested attributes after the base attributes have been set.
+      def assign_nested_parameter_attributes(pairs)
+        pairs.each { |k, v| _assign_attribute(k, v) }
+      end
+
       # Instantiates objects for all attribute classes that needs more than one constructor parameter. This is done
       # by calling new on the column type or aggregation type (through composed_of) object with these parameters.
       # So having the pairs written_on(1) = "2004", written_on(2) = "6", written_on(3) = "24", will instantiate

activerecord/test/cases/nested_attributes_test.rb

@@ -362,6 +362,15 @@ def test_should_work_with_update_as_well
     assert_equal "Mister Pablo", @pirate.ship.name
   end
 
+  def test_should_defer_updating_nested_associations_until_after_base_attributes_are_set
+    ship = @pirate.ship
+
+    ship_part = ShipPart.new
+    ship_part.attributes = { ship_attributes: { name: "Prometheus" }, ship_id: ship.id }
+
+    assert_equal "Prometheus", ship_part.ship.name
+  end
+
   def test_should_not_destroy_the_associated_model_until_the_parent_is_saved
     @pirate.attributes = { ship_attributes: { id: @ship.id, _destroy: "1" } }