Rails has_many，如何实现嵌套关联？

class User < ApplicationRecord
  has_many :posts
  accepts_nested_attributes_for :posts
end

class Post < ApplicationRecord
  belongs_to :user
end

<%= form_for @user do |f| %>
  <%= f.label :name %>
  <%= f.text_field :name %>

  <%= f.fields_for :posts do |p| %>
    <%= p.label :title %>
    <%= p.text_field :title %>
  <% end %>

  <%= f.submit %>
<% end %>

def user_params
  params.require(:user).permit(:name, posts_attributes: [:title])
end