Group By / Filters with UltraSphinx

Hi,

I use last version of UltraSphinx but filters dont work...

In my model : is_indexed :fields => ['content', 'titre', 'created_at', {:field => 'lang', :facet => true, :as => 'lang'}],                 :delta => true or is_indexed :fields => ['content', 'titre', 'created_at', 'lang'],                 :delta => true

In my controller : @search = Ultrasphinx::Search.new(:query => get_query_by_subject(@subject.id),                                         :sort_mode => 'descending',                                         :sort_by => 'created_at',                                         :weights => {'titre' => 5.0, 'content' => 2.0},                                         :page => params[:page] || 1,                                         :filters => {"lang" => "fr"})

Result : UsageError : field "lang" is invalid

:conditions => {"lang" => "fr"} doesnt work too.

I want to filter my results (lang, country, date, etc...) and group by title. Ultrasphinx doc doesnt speak about that. Just query work ^^

And I dont really understand what are "facets". Can you help me please ?

Thank you, Florian