named_scope :latest, :conditions => 'id in (select id from rank_histories rh where created_at = (select max(created_at) from rank_histories nested where nested.url = rh.url))'

RankHistory.find_by_sql('select * from rank_histories rh where created_at = (select max(created_at) from rank_histories nstd where nstd.url = rh.url)')

def create
  @partner = Partner.new(params[:partner])
  if(params[:partner_request_id])
...