Field collapsing on one of multiple models

[tom.ai...@gmail.com]

I am searching through three models like this:

  def self.multiquery q

    Sunspot.search Track, Site, Artist do |query_obj|

      query_obj.keywords q

      query_obj.paginate page: 1, per_page: 16

      query_obj.group :unique_track_id do

        limit 1000

      end

    end

  end

Only Track objects have a :unique_track_id and I only want to group those. Tracks get grouped as they should. What happens though is that all results for other models (Site, Artist) get grouped on :unique_track_id=nil. That is, the result looks like below. The first group contains all found Artist and Site, the others Track.

  SOLR Request (10.2ms)  [ path=#<RSolr::Client:0x00000008d83558> parameters={data: fq=type%3A%28Track+OR+Site+OR+Artist%29&q=country&fl=%2A+score&qf=title_text+artist_text+name_text&defType=dismax&start=0&rows=16&group=true&group.ngroups=true&group.field=unique_track_id_s&group.limit=1000, method: post, params: {:wt=>:ruby}, query: wt=ruby, headers: {"Content-Type"=>"application/x-www-form-urlencoded; charset=UTF-8"}, path: select, uri: http://localhost:8080/solr/select?wt=ruby, open_timeout: , read_timeout: , retry_503: , retry_after_limit: } ]

[

    [ 0] #<Sunspot::Search::Hit:Artist 15482>,

    [ 1] #<Sunspot::Search::Hit:Artist 11502>,

    [ 2] #<Sunspot::Search::Hit:Artist 8812>,

    [ 3] #<Sunspot::Search::Hit:Artist 7474>,

    [ 4] #<Sunspot::Search::Hit:Artist 7449>,

    [ 5] #<Sunspot::Search::Hit:Artist 7168>,

    [ 6] #<Sunspot::Search::Hit:Artist 6015>,

    [ 7] #<Sunspot::Search::Hit:Artist 1438>,

    [ 8] #<Sunspot::Search::Hit:Site 1840>,

    [ 9] #<Sunspot::Search::Hit:Site 1283>,

    [10] #<Sunspot::Search::Hit:Site 863>,

    [11] #<Sunspot::Search::Hit:Site 339>,

    [12] #<Sunspot::Search::Hit:Site 266>

]

[

    [0] #<Sunspot::Search::Hit:Track 4357>

]

[

    [0] #<Sunspot::Search::Hit:Track 2580>

]

[

    [0] #<Sunspot::Search::Hit:Track 2549>

]

[

    [0] #<Sunspot::Search::Hit:Track 1553>,

    [1] #<Sunspot::Search::Hit:Track 1524>,

    [2] #<Sunspot::Search::Hit:Track 1516>

]

My question is then, how can I group/collapse on only one model, for example Track? Is that even possible with Sunspot?

Thanks,

Tom