create_answers.rb

class CreateAnswers
  def initialize(params, user)
    @question_params = params
    @user = user
    @questionnaire_id = params["questionnaire_id"]
    @questionnaire_name = params["questionnaire_name"]
  end

  def run!
    create_answers
  end


  private

  def create_answers
    q = Questionnaire.find(@questionnaire_id)
    @user.questionnaires << q
    q.update(question_params)
  end

  def question_params
    @question_params.require(:questionnaire).permit(questions_attributes: [ :id, questionnaire_answer_attributes: [:description] ])
  end


end

gistfile1.txt

class Questionnaire < ApplicationRecord
  has_many :questions
  has_many :member_questionnaires
  has_many :users, through: :member_questionnaires
  accepts_nested_attributes_for :questions
end

class Question < ApplicationRecord
  belongs_to :questionnaire
  has_one :questionnaire_answer
  accepts_nested_attributes_for :questionnaire_answer
end

class QuestionnaireAnswer < ApplicationRecord
  belongs_to :question
end

new.haml

%h1
  questionnaire_answers#new

= form_for @questionnaire, url: questionnaire_answers_path, method: :post do |f|
  = hidden_field_tag 'questionnaire_id', @questionnaire.id
  = hidden_field_tag 'name', @questionnaire.name
  - @questionnaire.questions.each.with_index do |q, index|
    %h1
      = q.description
    = f.fields_for :questions, q do |question_fields|
      = question_fields.fields_for :questionnaire_answer, q.build_questionnaire_answer do |answer_fields|
        = answer_fields.text_field :description, id: index

  = f.submit "Save answers"

QuestionnaireAnswersController.rb

class QuestionnaireAnswersController < ApplicationController
  def new
    find_questionnaire
    @answer = QuestionnaireAnswer.new
  end

  def create
    @answers_creation = CreateAnswers.new(params, current_user)
    @answers_creation.run!
  end

  def edit

  end

  def update
  end

  private

  def find_questionnaire
    @questionnaire = Questionnaire.find(params[:id])
  end
end