    def underscore_key(key)
      k = key.to_s
      k = k.gsub(%r{(#{pluralize_special_cases.join("|")})}, "\\1s")
      k = underscore(k)
      k.gsub(%r{^id_([a-zA-Z_]+?)(s\b|\b)$}, "\\1_id\\2")
    end