Select integer parameter and Sunspot gem

Question

I just started learning to use Sunspot and Solr with Rails.

I followed this RailsCast http://railscasts.com/episodes/278-search-with-sunspot, but my problem is harder. So, how can I use parameter from select_tag with sunspot to search? My code:

**MODEL**
  searchable do 
    text :title, :content
    integer :city_id
  end   


**VIEW**
= form_tag vacancies_path, method: "get" do 
   = text_field_tag :search, params[:search], placeholder: "Search", class: "form-control"
   = select("city", "city_id", City.order(name: :asc).collect {|c| [ c.name, c.id ] }, {include_blank: 'Choose your city'}, class: "form-control")
   = submit_tag "Search", class: "btn btn-primary"


**CONTROLLER**
  def index
    @search = Vacancy.search do
      fulltext params[:search]

      with :city_id, params[:city][:city_id]
    end
    @vacancies = @search.results
  end


 **LOGS**
  Parameters: {"utf8"=>"✓", "search"=>"ruby", "city"=>{"city_id"=>"1973"}, "commit"=>"Искать"}
  SOLR Request (4.0ms)  [ path=select parameters={fq: ["type:Vacancy", "city_id_i:1973"], q: "ruby", fl: "* score", qf: "title_text content_text", defType: "edismax", start: 0, rows: 30} ]

It's not working. When I'm removing with :city_id, params[:city][:city_id] everything works fine except.. city filter. Thanks in advance.