Nested Forms with Strong Parameters; object_attribute method not available?

Question

This example is kind of cliche. I am following the railscasts episode #196 (http://railscasts.com/episodes/196-nested-model-form-revised?autoplay=true) for double nested forms.

The error I get is that my accepts_nested_attributes_for command is not generating an answers_attributes for strong parameters.

Models:

class Survey < ActiveRecord::Base
  has_many :questions
  accepts_nested_attributes_for :questions
end

class Question < ActiveRecord::Base
  belongs_to :survey
  has_many :answers
  has_many :users, through: :answers
  accepts_nested_attributes_for :answers
end

class Answer < ActiveRecord::Base
  belongs_to :question
  belongs_to :user
end

Then my surveys controller:

class SurveysController < ApplicationController

  def index
    @survey = current_user.surveys
  end

 def new
   @survey = Survey.new
   @question = @survey.questions.build   # the nested form won't show up if I don't
   @answer = @question.answers.build     #Not sure if I need this line. doesn't work either way.
 end

 def create
   @survey = Survey.new(survey_params)
   if @survey.save
     redirect_to @survey, notice: "Survey successfully created."
   else
     render 'new'
   end
 end

# rest.. show, edit, update, destroy


private

def survey_params
  params.require(:survey).permit! 
end

#def survey_params
  #params.require(:survey).permit(:user_id, :name, { questions_attributes: [:_destroy, :id, :survey_id, :content, { answers_attributes: [:_destroy, :id, :content, :user_id, :question_id]}]})
 #end 
end

The issue I'm having is this (empty form submit). When I run my real code, I get this:

{"utf8"=>"✓", "authenticity_token"=>"[token]=", "survey"=>{"user_id"=>"1", "name"=>"test", "questions_attributes"=>{"0"=>{"content"=>"test", "_destroy"=>"0"}}, "answers"=>{"content"=>"test", "_destroy"=>"0"}}, "commit"=>"Create", "action"=>"create", "controller"=>"surveys"}
Unpermitted attributes: answers

Then when I run the permit! method to test a force though I get this:

unknown attribute: answers

Rails should be looking for answers_attributes, not answers. That makes me think it's not recognizing the model. So, here is the schema.

create_table "questions", force: true do |t|
  t.integer  "survey_id"
  t.string   "content"
  t.datetime "created_at"
  t.datetime "updated_at"
end

create_table "answers", force: true do |t|
  t.integer  "question_id"
  t.string   "content"
  t.datetime "created_at"
  t.datetime "updated_at"
  t.integer  "user_id"
end

Let me know if you have any ideas on how to fix my error of somehow telling rails to look for answers instead of answers_attributes.

UPDATE: Here is my form.

<%= form_for @survey do |f| %>
<%= f.label :user_id %>


<%= f.collection_select :user_id, User.all, :id, :email, {}, { :multiple => false } %><br>
<%= f.text_field :name, placeholder: "Survey name"%>


<%= f.fields_for :questions do |builder| %>
  <%= builder.label :content, "Question 1"%>
  <%= builder.text_area :content %>
  <%= builder.check_box :_destroy %>
  <%= builder.label :_destroy, "Remove Question" %>

  <%= f.fields_for :answers do |builder| %>
    <%= builder.text_field :content, placeholder: "Answer 1" %>
    <%= builder.check_box :_destroy %>
  <% end %>
<% end %><br>

<%= f.submit "Create", :class => "btn btn-large btn-warning"  %>
<% end %>

Answer 1

The solution was an oversight on the forms. I used...

<%= f.fields_for :questions do |builder| %> 

...to build the association under the survey and then mistakenly used...

<%= f.fields_for :answers do |builder| %>

...to build the answers under question. I needed to change the f variable so it shoulder have been something like this:

<%= builder.fields_for :answers do |x| %>

So, it was looking for answers under survey instead of under questions. Thanks guys.