如何在rails视图中使用键值散列属性的输入？

def new
  @user = User.new
  @user.preferences = { color: 'blue', font_size: '12px' }
end

<%= form_for @user do |f| %>
  <%= f.fields_for :preferences do |pf| %>
    <%= pf.label :color %>
    <%= pf.text_field :color %>

    <%= pf.label :font_size %>
    <%= pf.text_field :font_size %>
  <% end %>

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

class User < ApplicationRecord
  serialize :preferences, JSON
end