未定义的方法`to_model＆＃39; 1：Fixnum

Question

艺术家/ show.html.erb

<% if @artist.songs.any? %>
  <div class="col-md-8">
    <% @artist.songs.each do |song| -%>
      <span><%= link_to song.title, song.artist  %></span>
    <% end -%>
  </div>
<% end %>

的routes.rb

  resources :artists, :path => "/Music", only: [:show] do
    resources :songs, :path => "/", only: [:show]
  end

艺术家控制器

class ArtistsController < ApplicationController
  def show
    @artist = Artist.friendly.find(params[:id])
  end
end

歌曲控制器

class SongsController < ApplicationController
  def show
    artist = Artist.friendly.find(params[:artist_id])
    @song = artist.songs.find(params[:id])
  end
end

艺术家模特

class Artist < ActiveRecord::Base
    extend FriendlyId
    friendly_id :name, use: :slugged

    has_many :songs, dependent: :destroy
    validates :name, presence: true, length: { maximum: 50 },
                     uniqueness: { case_sensitive: false }


  def slug=(value)
    if value.present?
      write_attribute(:slug, value)
    end
  end

end

歌曲模型

class Song < ActiveRecord::Base
  belongs_to :artist
  default_scope -> { order(:title) }
  validates :artist_id, presence: true
  validates :title,     presence: true,
                        length: { maximum: 140 }



  rails_admin do
    configure :artist do
      label 'artist name: '
    end
  end

的Gemfile

source 'https://rubygems.org'

gem 'rails',                '4.2.1'
gem 'friendly_id', '~> 5.1.0'
gem 'sorcery'
gem 'validates_email_format_of'
gem 'bootstrap-sass',       '3.2.0.0'
gem 'sqlite3',              '1.3.10'
gem 'uglifier',             '>= 1.3.0'
gem 'coffee-rails', '~> 4.1.0'
gem 'jquery-rails'
gem 'turbolinks'
gem 'jbuilder',             '~> 2.0'
gem 'sdoc',                 '0.4.0', group: :doc
gem 'delayed_job_active_record'
gem 'rails_admin'
gem 'font-awesome-sass-rails' 
gem 'coffee-script-source', '1.8.0'

group :development, :test do
  gem 'byebug'
  gem 'web-console', '~> 2.0'
  gem 'minitest' 
end



gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]

当我进入 http://localhost:3000/Music/ed-sheeran

它给我这个错误信息

 undefined method `to_model' for 1:Fixnum

我可能遗漏了一些明显的东西。