ruby on rails - Filtering by value calculated in instance method -

i have house model has price attribute calculated using instance method.

let's price changing due market rates, inflation, etc. need price_today method current price.

how can create named scope (or something) filter houses using maximum price , minimum price?

i tried doing this, feel it's little hacky...

  def index     @houses = # houses db      if not params[:max_price].nil?       @houses.keep_if { |h|  h.price_today <= params[:max_price].to_f }     end      if not params[:min_price].nil?       @houses.keep_if { |h| h.price_today >= params[:min_price].to_f }     end   end 

a named scope (or where clause) faster querying , filtering instantiated objects.
however, i'm afraid if price_today not exist in db won't able use them.

you can improve code, though.
conditions can made simpler, , can use single call keep_if.

max = params[:max_price].presence min = params[:min_price].presence  if max || min   @houses.keep_if |house|     = max ? (house.price_today <= max.to_f) : true     b = min ? (house.price_today >= min.to_f) : true     && b   end end 

if want, instead of keep_if can use select.