具有活动管理功能的Rails双层嵌套表单

# app/models/event.rb
class Event < ApplicationRecord
  has_many :participants, dependent: :destroy
  accepts_nested_attributes_for :participants, allow_destroy: true
end

# app/models/participant.rb
class Participant < ApplicationRecord
  belongs_to :event
  has_many :contacts, dependent: :destroy
  accepts_nested_attributes_for :contacts, allow_destroy: true
end

# app/models/contact.rb
class Contact < ApplicationRecord
  belongs_to :participant
end

# app/controllers/events_controller.rb
class EventsController < ApplicationController
  def new
    @event = Event.new
    @event.participants.build
    @event.participants.first.contacts.build
  end

  def create
    @event = Event.new(event_params)
    if @event.save
      redirect_to @event, notice: 'Event was successfully created.'
    else
      render :new
    end
  end

  private

  def event_params
    params.require(:event).permit(:name, participants_attributes: [:id, :_destroy, contacts_attributes: [:id, :type, :value, :_destroy]])
  end
end

<!-- app/views/events/new.html.erb -->
<%= form_with(model: @event, local: true) do |form| %>
  <% if @event.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@event.errors.count, "error") %> prohibited this event from being saved:</h2>

      <ul>
        <% @event.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 :participants do |participant_fields| %>
    <div class="field">
      <%= participant_fields.label :name %>
      <%= participant_fields.text_field :name %>
    </div>

    <%= participant_fields.fields_for :contacts do |contact_fields| %>
      <div class="field">
        <%= contact_fields.label :type %>
        <%= contact_fields.text_field :type %>
      </div>

      <div class="field">
        <%= contact_fields.label :value %>
        <%= contact_fields.text_field :value %>
      </div>
    <% end %>
  <% end %>

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

def event_params
  params.require(:event).permit(:name, participants_attributes: [:id, :_destroy, contacts_attributes: [:id, :type, :value, :_destroy]])
end

<%= form.fields_for :participants do |participant_fields| %>
  <!-- participant fields -->
  <%= participant_fields.fields_for :contacts do |contact_fields| %>
    <!-- contact fields -->
  <% end %>
<% end %>