Add excerpt column to topics table to remove N+1 query in ListableTopicSerializer

lib/post_revisor.rb

@@ -14,6 +14,7 @@ class PostRevisor
     @post.acting_user = @user
     revise_post
     update_category_description
+    update_topic_excerpt
     post_process_post
     update_topic_word_counts
     @post.advance_draft_sequence
@@ -107,6 +108,10 @@ class PostRevisor
     end
   end
 
+  def update_topic_excerpt
+    @post.topic.update_column(:excerpt, @post.excerpt(220, strip_links: true)) if @post.post_number == 1
+  end
+
   def post_process_post
     @post.invalidate_oneboxes = true
     @post.trigger_post_process