Fixes restoring polymorphic has_one relationships

If the association object is a has_one relationship with an :as option,
it will have a type attribute (see
https://github.com/rails/docrails/blob/master/activerecord/lib/active_record/reflection.rb#L280).

If this type attributes is present, that will be the type column on the
polymorphic model. The foreign key can be found as an attribute on
the association object.

lib/paranoia.rb

@@ -143,8 +143,16 @@ module Paranoia
 
       if association_data.nil? && association.macro.to_s == "has_one"
         association_class_name = association.options[:class_name].present? ? association.options[:class_name] : association.name.to_s.camelize
-        association_foreign_key = association.options[:foreign_key].present? ? association.options[:foreign_key] : "#{self.class.name.to_s.underscore}_id"
-        Object.const_get(association_class_name).only_deleted.where(association_foreign_key => self.id).first.try(:restore, recursive: true)
+        association_foreign_key = association.foreign_key.present? ? association.foreign_key : "#{self.class.name.to_s.underscore}_id"
+
+        if association.type
+          association_polymorphic_type = association.type
+          association_find_conditions = { association_polymorphic_type => self.class.name.to_s, association_foreign_key => self.id }
+        else
+          association_find_conditions = { association_foreign_key => self.id }
+        end
+
+        Object.const_get(association_class_name).only_deleted.where(association_find_conditions).first.try(:restore, recursive: true)
       end
     end