instance method define_method_attribute=

# File activerecord/lib/active_record/readonly_attributes.rb, line 62
        def define_method_attribute=(canonical_name, owner:, as: canonical_name)
          if ActiveRecord._raise_on_assign_to_attr_readonly && readonly_attribute?(canonical_name)
            ActiveModel::AttributeMethods::AttrNames.define_attribute_accessor_method(
              canonical_name, writer: true,
            ) do |temp_method_name, attr_name_expr|
              owner.define_cached_method(temp_method_name, as: "#{as}=", namespace: :active_record_readonly) do |batch|
                batch <<
                  "def #{temp_method_name}(value)" <<
                  "  unless new_record?" <<
                  "    raise ActiveRecord::ReadonlyAttributeError.new(#{attr_name_expr})" <<
                  "  end" <<
                  "  @attributes.write_from_user(#{attr_name_expr}, value)" <<
                  "end"
              end
            end
          else
            super
          end
        end