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

db/migrate/20140318150412_add_excerpt_to_topics.rb

@@ -0,0 +1,18 @@
+class AddExcerptToTopics < ActiveRecord::Migration
+  def up
+    add_column :topics, :excerpt, :string, limit: 1000
+
+    topic_ids = execute("SELECT id FROM topics WHERE pinned_at IS NOT NULL").map {|r| r['id'].to_i }
+    topic_ids.each do |topic_id|
+      cooked = execute("SELECT cooked FROM posts WHERE topic_id = #{topic_id} ORDER BY post_number ASC LIMIT 1")[0]['cooked']
+      if cooked
+        excerpt = ExcerptParser.get_excerpt(cooked, 220, strip_links: true)
+        execute "UPDATE topics SET excerpt = #{ActiveRecord::Base.sanitize(excerpt)} WHERE id = #{topic_id}"
+      end
+    end
+  end
+
+  def down
+    remove_column :topics, :excerpt
+  end
+end