Rails 4 - Salvar Array de Selects

_form.html.slim

= simple_form_for @page do |f|
  = f.error_notification

  .form-inputs
    = f.input :title
    = f.association :section

  .panel.panel-default
    .panel-heading
      .panel-title Definir direcionamento da página
    .panel-body
      .form-inline
        .form-group
          = f.input :ensuing, label: false, collection: [ "Enviar para", "Objetivo", "Pergunta", "Tag" ], include_blank: false, :input_html => { :id => "first_select", :name => 'page[ensuing][]' }
        .form-group
          = f.input :ensuing, label: false, collection: Question.order(:title), include_blank: false, prompt: "Selecione a pergunta", :input_html => { :id => "question_select", :name => 'page[ensuing][]' }
        .form-group
          = f.input :ensuing, label: false, collection: Question.order(:title), as: :grouped_select, as: :grouped_select, group_method: :answer_options, label_method: :content, value_method: :content, include_blank: false,  :input_html => { :id => "answer_option_select", :name => 'page[ensuing][]' }
        .form-group
          = f.input :ensuing, label: false, collection: Page.order(:title), include_blank: false, prompt: "Enviar para", :input_html => { :id => "next_select", :name => 'page[ensuing][]' }

  .form-actions
    = f.button :submit, class: 'btn btn-success'

page.rb

class Page < ActiveRecord::Base

  belongs_to :section
  has_many :questions
  has_many :posts

  has_one :previous, :class_name => "Page", :foreign_key => "next_id"
  belongs_to :ensuing, :class_name => "Page"

  serialize :ensuing, Array if Rails.env.development?

end

pages_controller.rb

class PagesController < ApplicationController
  before_action :set_page, only: [:show, :edit, :update, :destroy]

  # POST /pages
  # POST /pages.json
  def create
    @page = Page.new(page_params)

    respond_to do |format|
      if @page.save
        format.html { redirect_to @page, notice: 'Page was successfully created.' }
        format.json { render :show, status: :created, location: @page }
      else
        format.html { render :new }
        format.json { render json: @page.errors, status: :unprocessable_entity }
      end
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_page
      @page = Page.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def page_params
      
      params.require(:page).permit(:title, :section_id, ensuings: [])
    end
end