rails force execution of SQL query in where clause

this is the code that i have:

list_views = ListView.where(:user_id => current_user.id)
total_list_views = list_views.size
top_recommended_lists = recommendations_based_on_list_views(list_views, language_score_hash, level_score_hash, category_score_hash)

and then there is this method

def recommendations_based_on_list_views(list_views, language_score_hash, level_score_hash, category_score_hash)
  viewed_lists_ids = list_views.map {|list_view| list_view.list_id}.uniq
  ....

problem is with this code 2 queries are executed on ListView model one at list_views.size and then at list_views.map {|list_view| list_view.list_id}.uniq

if we can force query execution at ListView.where(:user_id => current_user.id) then only single query to ListView model will be needed OR if any other way

how to achieve this ??