title: Undefined method 'album_url' when deleting a photo and redirecting
body: <p>I have user, album, and photo models set up as the following:</p>
  
  <p><strong>user.rb</strong></p>
  
  <pre><code>class User &lt; ActiveRecord::Base
    devise :database_authenticatable, :registerable,
           :recoverable, :rememberable, :trackable, :validatable
  
    has_many :albumusers
    has_many :albums, through: :albumusers, :foreign_key =&gt; :album_id
  
  end
  </code></pre>
  
  <p><strong>album.rb</strong></p>
  
  <pre><code>class Album &lt; ActiveRecord::Base
      validates :name, presence: true
  
      has_many :photos
  
      has_many :albumusers
      has_many :users, through: :albumusers, :foreign_key =&gt; :user_id
  end
  </code></pre>
  
  <p><strong>photo.rb</strong></p>
  
  <pre><code>class Photo &lt; ActiveRecord::Base
      belongs_to :album
  
      mount_uploader :image, PhotoUploader
  
      before_create :default_title
  
      def default_title
          self.title ||= File.basename(image.filename, '.*').titleize if image
      end
  end
  </code></pre>
  
  <p><strong>albumuser.rb</strong></p>
  
  <pre><code>class Albumuser &lt; ActiveRecord::Base
      belongs_to :user
      belongs_to :album
  end
  </code></pre>
  
  <p><strong>routes.rb</strong></p>
  
  <pre><code>resources :users do
      resources :albums do
          resources :photos
      end
  end
  </code></pre>
  
  <p><strong>photo_controller.rb</strong></p>
  
  <pre><code>  def destroy
      @photo = Photo.find(params[:id])
      @photo.destroy
      flash[:notice] = "Successfully deleted photo"
      redirect_to @photo.album # ERROR is happening here
    end
  </code></pre>
  
  <p>When I try to delete a photo, I get error when trying to redirect back to the album show view.</p>