Alter previous method on all versions models

This is to prevent redoing the same SQL query which wasn't being cached.

app/models/artist_commentary_version.rb

@@ -7,4 +7,11 @@ class ArtistCommentaryVersion < ApplicationRecord
     q = q.search_attributes(params, :post, :updater, :original_title, :original_description, :translated_title, :translated_description)
     q.apply_default_order(params)
   end
+
+  def previous
+    @previous ||= begin
+      ArtistCommentaryVersion.where("post_id = ? and updated_at < ?", post_id, updated_at).order("updated_at desc").limit(1).to_a
+    end
+    @previous.first
+  end
 end