Single query solution to finding nearest donees with matching timeslots

sample.rb

  def donees_in_radius_with_timeslots(radius)
    required_bits = 2**User.valid_roles.index(:donee)
    Location.near(self.location, 
                  radius, 
                  :select => "locations.*, users.*, time_slots.*"
                 ).joins(:user => :time_slots)
                  .where(["roles_mask & ? > 0", required_bits])
                  .where(["roles_mask & ? > 0", required_bits])
  end