Rails query for all questions in tournaments that a user participates in
Ok, so based on what your said your associations are you can do

class User
  has_many :tournaments
  has_many :questions, through: :tournaments
end

u = User.first
questions = u.questions


If you don't want that for some reason you can do

class User
  has_many :tournaments
end

class Question
  belongs_to :tournament
end

u = User.first
questions = Question.where(tournament_id: u.tournament_ids)


Rails will convert that into a where tournament_id in (?) sql statement