gistfile1.rb

def create
  offer = Offer.find(params[:offer_id])
  if params[:offer_id]
    task = JSON.parse(params[:tasks])
    unless task.nil?
      # seleziona i parametri rispondenti alla RE active_(.*)
      # in questo modo otterrai una lista "elems" di al max 3 elementi del tipo 
      # elems == ['active_gift', 'active_encoding', ...]
      elems.each do |elem|
        klass_name = elem.split('_')[1].capitalize
        klass = eval klass_name

        # a questo punto hai la classe klass che equivale a Gift, Encoding, etc.
        task, elem_instance = klass.separate(task)

        if task.class == Hash and !task["id"].empty?
          task_id = task["id"]
          new_task = Task.find(task_id)
          new_task.update_attributes(task)
          if task["active_#{elem}"]
            delete_elem = klass.find_by_task_id(task_id)
            delete_elem.delete unless delete_elem.nil?
            new_task.send(elem, klass.new(elem_instance))
            new_task.save
          else
            ...
          elsif task.class == Array 
            ...
          else
            ...
            if task["active_#{elem}"]
              ...
            else
              ...
            end
          end
        end
      else
        render :json => @service.to_ext_json(:success => @service.update_attributes(params[:service]))
      end
    end
  end
end