Add order on topic index.

app/controllers/communities_controller.rb

@@ -1,6 +1,8 @@
 class CommunitiesController < ApplicationController
 
-  before_action :set_community, :load_topics, only: :show
+  before_action :set_order, :set_community, :load_topics, only: :show
+
+  has_orders %w{newest most_commented oldest}, only: :show
 
   skip_authorization_check
 
@@ -9,11 +11,15 @@ class CommunitiesController < ApplicationController
 
   private
 
+  def set_order
+    @order = params[:order].present? ? params[:order] : "newest"
+  end
+
   def set_community
     @community = Community.find(params[:id])
   end
 
   def load_topics
-    @topics = @community.topics.page(params[:page])
+    @topics = @community.topics.send("sort_by_#{@order}").page(params[:page])
   end
 end