Deep Nested Rails 4 Form

问题

I have 3 models Item which accepts nested attributes for questions and questions accept nested attributes for answers. I'm trying to create an item which has a question and an answer in the same form.

item.rb

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

The form is being displayed correctly and it saves the question model correctly. I can't seem to save the answer though.

I've already looked at a lot of online help but none are covering it with Rails 4 strong params.

回答1:

I think your problem is with your strong params:

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

Basically, when you pass a deep nested form (where you have multiple dependent models), you'll have to pass the attributes as part of the other model's attributes. You had the params as separate

回答2:

I run into a similar issue and, while Richard Peck answer helped me as well, there is one thing that it was missing for me.

If you are deep-nesting you need to specify the id of the parent of the nested item. In this case to create an answers you need to make questions id explicit with q.input :id, otherwise you will run into this error.

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

来源：https://stackoverflow.com/questions/20992959/deep-nested-rails-4-form