I have a Track that has_many Quizzes and a Quiz has_many Questions.
quiz.rb:
class Quiz < ActiveRecord::Base
  belongs_to :track
  has_many :questions, dependent: :destroy
  accepts_nested_attributes_for :questions
end
question.rb:
class Question < ActiveRecord::Base
  belongs_to :quiz
end
quizzes_controller.rb:
def new
  @quiz = Quiz.new
  @track = Track.find(params[:permalink])
  @course = Course.find(@track.course_id)
  3.times { @quiz.questions.build }
end
def create
  @track = Track.find(params[:permalink])
  @quiz = @track.quizzes.build(quiz_params)
  @course = Course.find(@track.course_id)
  if @quiz.save
    flash[:success] = 'Quiz successfully created'
    redirect_to quiz_path @quiz
  else
    redirect_to track_path @track
  end
end
private
def quiz_params
  params.require(:quiz).permit(:name, :information, :order, 
                               :permalink, :user_id,
                               questions_attributes: [:id, :content])
end
params on submit:
{"utf8"=>"✓",
 "authenticity_token"=>"...",
 "quiz"=> {
   "name"=>"Test Quiz",
   "questions_attributes"=> {
     "0"=>{"content"=>"This is question 1?"},
     "1"=>{"content"=>"This is question 2?"},
     "2"=>{"content"=>""}
   }, "user_id"=>"1",
   "order"=>"3"
 }, "commit"=>"Submit",
 "permalink"=>"1-basics"}
When I press submit the quiz is created but the questions are not created.
New params:
def quiz_params
    params.require(:quiz).permit(:name, :information, :order, 
                                 :permalink, :user_id, 
                                 questions_attributes: [:id, :content, :_destroy, answers_attributes: [:id, :content, :_destroy]] )
  end