gistfile1.rb

module ActiveModel
  class Serializer
    module Associations
      class HasOne < Config
        def root
          if root = option(:root)
            root
          elsif polymorphic?
            polymorphic_name.pluralize.to_sym
          else
            @name.to_s.pluralize.to_sym
          end
        end

        def polymorphic_key
          polymorphic_name.to_sym
        end

        private
        def polymorphic_name
          associated_object.active_model_serializer.name.demodulize.gsub("Serializer", "").underscore
        end
      end
    end
  end
end

class Admin
  def active_model_serializer
    SuperUserSerializer
  end
end