问在rails简单表单中嵌入/嵌套多个表单的最佳方法是什么？

EN

belongs_to :books
has_many :images
accepts_nested_attributes_for :books
accepts_nested_attributes_for :images, :allow_destroy => true

 class GalleriesController < ApplicationController
  before_action :set_gallery, only: [:show, :edit, :update, :destroy]

  def index
    @galleries = Gallery.all
  end

  def show
  end

  def new
    @gallery = Gallery.new
  end

  def edit
  end
  def create
    @gallery = Gallery.new(gallery_params)
  end

  def update
  end

  def destroy
    @gallery.destroy
  end

  private
    def set_gallery
      @gallery = Gallery.find(params[:id])
    end
    def gallery_params
      params.require(:gallery).permit(:name, :book_id)
    end
end

belongs_to :gallery
    has_attached_file :file, :styles => { :medium => "300x300>", :thumb => "100x100>" }, :default_url => "/images/:style/missing.png"
    validates_attachment_content_type :file, :content_type => /\Aimage\/.*\Z/

belongs_to :author
has_one :gallery

accepts_nested_attributes_for :author
accepts_nested_attributes_for :gallery

gem 'simple_form'
gem 'nested_form'

<%= simple_form_for(@gallery, html: { multipart: true }) do |f| %>
  <%= f.error_notification %>

  <div class="inputs">
    <%= f.input :name %>
    <%= f.input :book_id %>
    <%= f.simple_fields_for :image do |a| %>
        <%#= f.input :picture %>
        <%#= a.file_field :file %>
        <%= f.input_field :file, as: :file, multiple: true, name: 'gallery[image]' %>
    <% end %>
  </div>

  <div class="actions">
    <%= f.button :submit %>
  </div>
<% end %>

undefined method `simple_nested_form_for' for #<SimpleForm::FormBuilder:0x00000104d52640

<%= simple_form_for(@book, :html => { :multipart => true }) do |f| %>    
<%= f.simple_nested_form_for (@gallery) do |t| %>
    <%= t.simple_fields_for :gallery do |t| %>
    <%= render 'galleries/form' %>
    <% end %>
    <% end %>
<% end %>