ruby-on-rails – 深嵌套导轨4表格

item.rb的

class Item < ActiveRecord::Base
  has_many :questions,dependent: :destroy
  accepts_nested_attributes_for :questions
end

question.rb

class Question < ActiveRecord::Base
  belongs_to :item

  has_many :answers,dependent: :destroy
  accepts_nested_attributes_for :answers
end

answer.rb

class Answer < ActiveRecord::Base
  belongs_to :question
end

item_controller.rb

class ItemsController < ApplicationController
    def new
      @item = @repository.items.new
      questions = @item.questions.build
      answers = questions.answers.build
    end

    def create
      @item = Item.new(item_params)
      if @item.save
          redirect_to @item,notice: '...'
      else
          render action: 'new'
      end
    end

  private
  def item_params
      params.require(:item).permit(:id,:content,:kind,:questions_attributes => [:content,:helper_text,:kind],:answers_attributes => [:content,:correct])
  end   
end

_form.haml

= simple_form_for(@item) do |f|
    = f.input :kind
    = f.input :content
    = f.simple_fields_for :questions do |q|
        = q.input :content
        = q.simple_fields_for :answers do |a|
            = a.input :content
    = f.submit

表单正确显示,并正确保存问题模型.我似乎无法保存答案.

我已经看过很多在线帮助,但没有人用Rails 4强大的参数覆盖它.