クエリ・パフォーマンスの改善（#258） (#259)

#258

#258

#258

Co-authored-by: miteruzo <miteruzo@naver.com>
Reviewed-on: #259

backend/app/models/post.rb

@@ -30,13 +30,15 @@ class Post < ApplicationRecord
     super(options).merge(thumbnail: nil)
   end
 
-  def related(limit: nil)
-    ids = post_similarities.select(:target_post_id).order(cos: :desc)
+  def related limit: nil
+    ids = post_similarities.order(cos: :desc)
     ids = ids.limit(limit) if limit
     ids = ids.pluck(:target_post_id)
-    return [] if ids.empty?
+    return Post.none if ids.empty?
 
-    Post.where(id: ids).order(Arel.sql("FIELD(id, #{ ids.join(',') })"))
+    Post.where(id: ids)
+        .with_attached_thumbnail
+        .order(Arel.sql("FIELD(posts.id, #{ ids.join(',') })"))
   end
 
   def resized_thumbnail!