Rails嵌套强参数，如何使用？

class Author < ApplicationRecord
  has_many :books
  accepts_nested_attributes_for :books
end

class Book < ApplicationRecord
  belongs_to :author
end

class AuthorsController < ApplicationController
  def create
    @author = Author.new(author_params)
    if @author.save
      redirect_to @author, notice: 'Author was successfully created.'
    else
      render :new
    end
  end

  private

  def author_params
    params.require(:author).permit(
      :name,
      books_attributes: [:title, :published_date]
    )
  end
end

<%= form_with(model: @author, local: true) do |form| %>
  <% if @author.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@author.errors.count, "error") %> prohibited this author from being saved:</h2>
      <ul>
        <% @author.errors.full_messages.each do |message| %>
          <li><%= message %></li>
        <% end %>
      </ul>
    </div>
  <% end %>

  <div class="field">
    <%= form.label :name %>
    <%= form.text_field :name %>
  </div>

  <%= form.fields_for :books do |book_form| %>
    <div class="field">
      <%= book_form.label :title %>
      <%= book_form.text_field :title %>
    </div>
    <div class="field">
      <%= book_form.label :published_date %>
      <%= book_form.date_select :published_date %>
    </div>
  <% end %>

  <div class="actions">
    <%= form.submit %>
  </div>
<% end %>