quotations_controller.rb

class QuotationsController  < ApplicationController
  def index
    @params = QuotationsIndexParams.new(params)
    (redirect_to request.referer || quotations_path, :error => "Bad Request", :status => 400 and return) unless @params.valid?
    @quotations = Quotation.search(@params.search_params).
                            send(@params.scope, @params.scope_params).
                            sorted_by(@params.sort.to_sym).
                            page(params[:page])
    respond_to do |format|
      format.html # index.html.erb
      format.json { render json: @quotations }
      format.csv
    end
  end

  ...

end