Rails Ancestry undefined方法`model_name'用于NilClass：Class

Question

我正在努力学习如何使用“Ancestry”宝石。我在Railscast中观看了相关剧集并获取了代码。 message表工作正常。但我正在尝试使用名为locations的新表复制它。我已复制并更改了所有代码的名称（我相信）。

我创建了第一个位置。但是，当我转到localhost:3000/locations时，我会为NilClass获取undefined method model_name'：类for _ form.html.erb`行：

<%= form_for @location do |f| %>

routes.rb：

  Messenger::Application.routes.draw do
    resources :locations
    resources :messages
    root :to => 'messages#index'
  end

_form.html.erb：

<%= form_for @location do |f| %>
  <%= f.error_messages %>
  <%= f.hidden_field :parent_id %>
  <p>
  <%= f.label :locname, "New Location" %><br />
  <%= f.text_area :locname, :rows => 8 %>
  </p>
  <p><%= f.submit "Post Location" %></p>
<% end %>

index.html.erb：

<% title "Locations" %>
<%= nested_locations @locations.arrange(:order => :created_at) %>
<%= render "form" %>

locations_controller.rb：

class LocationsController < ApplicationController
  def index
    @locations = Location.scoped
  @location = Location.new
end

def show
  @location = Location.find(params[:id])
end

def new
  @location = Location.new(:parent_id => params[:parent_id])
end

def create
  @location = Location.new(params[:location])
  if @location.save
    redirect_to locations_url
  else
  render :new
  end
end

def destroy
  @location = Location.find(params[:id])
  @location.destroy
  redirect_to locations_url
end

端

locations_helper.rb：

 module LocationsHelper
  def nested_locations(locations)
    locations.map do |location, sub_locations|
      render(location) + content_tag(:div, nested_locations(sub_locations), :class => "nested_locations")
   end.join.html_safe
 end
end