在Rails中动态生成三层深度的嵌套表单

class Parent < ApplicationRecord
  has_many :children
  accepts_nested_attributes_for :children, allow_destroy: true
end

class Child < ApplicationRecord
  belongs_to :parent
  has_many :grandchildren
  accepts_nested_attributes_for :grandchildren, allow_destroy: true
end

class Grandchild < ApplicationRecord
  belongs_to :child
end

<%= form_for @parent do |f| %>
  <%= f.fields_for :children do |child_form| %>
    <%= child_form.text_field :name %>
    <%= child_form.fields_for :grandchildren do |grandchild_form| %>
      <%= grandchild_form.text_field :name %>
    <% end %>
  <% end %>
  <%= f.submit %>
<% end %>

class ParentsController < ApplicationController
  def new
    @parent = Parent.new
    @parent.children.build
    @parent.children.each { |child| child.grandchildren.build }
  end

  def create
    @parent = Parent.new(parent_params)
    if @parent.save
      redirect_to @parent
    else
      render :new
    end
  end

  private

  def parent_params
    params.require(:parent).permit(
      :name,
      children_attributes: [
        :id,
        :name,
        grandchildren_attributes: [
          :id,
          :name,
          :_destroy
        ]
      ]
    )
  end
end