subtract from symbols in ruby -

i find first valid image among list in ruby. here code:

 if(params[:id])     @image = image.find_by_id(params[:id])    while @image.nil?     :id-- ?     @image = image.find_by_id(params[:id])    end

in block, how can keep decreasing id # until valid image found? :/

thanks!

you can't subtract symbol. symbol not number.

what seem want decrease value of params[:id], of course possible (after converting id string integer) doing params[:id] = params[:id].to_i - 1 or

id = params[:id].to_i while @image.nil?   @image = image.find_by_id(id)   id -= 1 end

the latter better first because not mutate params (which there no reason do).

however should not either of those, because can achieve much less hassle, letting db work:

image.find(:first, :order => "id desc", :conditions => ["id <= ?", params[:id]])

ps: ruby doesn't have -- operator, have use -= 1 decrement number.

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