PERF: eliminate N+1 query due to polls

lib/topic_view.rb

@@ -433,7 +433,14 @@ class TopicView
   end
 
   def closest_post_to(post_number)
-    closest_post = @filtered_posts.order("@(post_number - #{post_number})").limit(1).pluck(:id)
+    # happy path
+    closest_post = @filtered_posts.where("post_number = ?", post_number).limit(1).pluck(:id)
+
+    if closest_post.empty?
+      # less happy path, missing post
+      closest_post = @filtered_posts.order("@(post_number - #{post_number})").limit(1).pluck(:id)
+    end
+
     return nil if closest_post.empty?
 
     filtered_post_ids.index(closest_post.first) || filtered_post_ids[0]

plugins/poll/plugin.rb

@@ -14,6 +14,15 @@ VOTES_CUSTOM_FIELD ||= "polls-votes".freeze
 
 after_initialize do
 
+  # PERF, avoids N+1 in serializer
+  TopicView.add_post_custom_fields_whitelister do |user|
+    POLLS_CUSTOM_FIELD
+  end
+
+  TopicView.add_post_custom_fields_whitelister do |user|
+    VOTES_CUSTOM_FIELD
+  end
+
   # remove "Vote Now!" & "Show Results" links in emails
   Email::Styles.register_plugin_style do |fragment|
     fragment.css(".poll a.cast-votes, .poll a.toggle-results").each(&:remove)