gistfile1.txt

controller
def create
 32       params[:question][:subjects].delete_if { |n| n == "" }
 33       Question.create(:title => params[:question][:title],
 34                       :summary => params[:question][:summary],
 35                       :subject_id => params[:question][:subjects])
 36    end

model
  1 class Question < ActiveRecord::Base
  2   belongs_to :user
  3   has_many :subjects
  4   has_many :answers
  5 end

view
<div><%= f.label :subjects %></div>
  9
 10   <div><%= f.collection_check_boxes(:subjects, Subject.all, :id, :name) %></    div>