AI: address issue #439

backend/app/controllers/posts_controller.rb

@@ -314,7 +314,9 @@ class PostsController < ApplicationController
   def viewed
     return head :unauthorized unless current_user
 
-    current_user.viewed_posts << Post.find(params[:id])
+    UserPostView.create_or_find_by!(
+        user: current_user,
+        post: Post.find(params[:id]))
     head :no_content
   end