Use an instance variable to store the current masss assignment options

activerecord/lib/active_record/base.rb

@@ -1709,27 +1709,24 @@ def assign_attributes(new_attributes, options = {})
         return unless new_attributes
 
         attributes = new_attributes.stringify_keys
-        role = options[:as] || :default
-
         multi_parameter_attributes = []
+        @mass_assignment_options = options
 
         unless options[:without_protection]
-          attributes = sanitize_for_mass_assignment(attributes, role)
+          attributes = sanitize_for_mass_assignment(attributes, mass_assignment_role)
         end
 
         attributes.each do |k, v|
           if k.include?("(")
             multi_parameter_attributes << [ k, v ]
+          elsif respond_to?("#{k}=")
+            send("#{k}=", v)
           else
-            method_name = "#{k}="
-            if respond_to?(method_name)
-              method(method_name).arity == -2 ? send(method_name, v, options) : send(method_name, v)
-            else
-              raise(UnknownAttributeError, "unknown attribute: #{k}")
-            end
+            raise(UnknownAttributeError, "unknown attribute: #{k}")
           end
         end
 
+        @mass_assignment_options = nil
         assign_multiparameter_attributes(multi_parameter_attributes)
       end
 
@@ -1894,6 +1891,14 @@ def clone_attribute_value(reader_method, attribute_name)
         value
       end
 
+      def mass_assignment_options
+        @mass_assignment_options ||= {}
+      end
+
+      def mass_assignment_role
+        mass_assignment_options[:as] || :default
+      end
+
     private
 
       # Under Ruby 1.9, Array#flatten will call #to_ary (recursively) on each of the elements

activerecord/lib/active_record/nested_attributes.rb

@@ -276,15 +276,15 @@ def accepts_nested_attributes_for(*attr_names)
 
             type = (reflection.collection? ? :collection : :one_to_one)
 
-            # def pirate_attributes=(attributes, assignment_opts = {})
-            #   assign_nested_attributes_for_one_to_one_association(:pirate, attributes, assignment_opts)
+            # def pirate_attributes=(attributes)
+            #   assign_nested_attributes_for_one_to_one_association(:pirate, attributes, mass_assignment_options)
             # end
             class_eval <<-eoruby, __FILE__, __LINE__ + 1
               if method_defined?(:#{association_name}_attributes=)
                 remove_method(:#{association_name}_attributes=)
               end
-              def #{association_name}_attributes=(attributes, assignment_opts = {})
-                assign_nested_attributes_for_#{type}_association(:#{association_name}, attributes, assignment_opts)
+              def #{association_name}_attributes=(attributes)
+                assign_nested_attributes_for_#{type}_association(:#{association_name}, attributes, mass_assignment_options)
               end
             eoruby
           else