viewings idea

# config/routes.rb

Threads::Application.routes.draw do
  #...existing stuff

  resources :topics, only: [:index, :create, :show] do
    resources :posts, only: [:index, :create, :show]
  end

  resources :settings, only: [:index]

  match '/topics/:topic_id/viewings' => 'viewings#create', :via => :post
end

# app/controllers/viewings_controller.rb

class ViewingsController < ApplicationController
  def create
    topic = Topic.find(params[:topic_id])
    topic.view_count += 1

    if topic.save
      render text: '', status: 200 
    else
      # handle errors
    end

    # in the future you could set other data you need here, eg: a timestamp on current_user for 
    # purposes of figuring out how many posts were added since you last looked at the topic
  end
end

# app/assets/javascripts/router.js.coffee

class Threads.Router extends Backbone.Router
  # existing stuff..

  show: (topicId) ->
    @_topics.fetch().done =>
      topic = @_topics.get topicId
      topic.posts().fetch
        success: ->
          Threads.app.renderContent new Threads.Views.Show topic: topic
          $.post "/topics/#{topicId}/viewings"

  #...