backend/app/controllers/posts_controller.rb

@@ -36,8 +36,8 @@ class PostsController < ApplicationController
     offset = (page - 1) * limit
 
     pt_max_sql =
-        PostTag
-        .select('post_id, MAX(updated_at) AS max_updated_at')
+        PostVersion
+        .select('post_id, MAX(created_at) AS max_updated_at')
         .group('post_id')
         .to_sql
 

backend/app/models/post.rb

@@ -56,6 +56,9 @@ class Post < ApplicationRecord
 
   has_many :post_tags, dependent: :destroy, inverse_of: :post
   has_many :tags, through: :post_tags
+  has_many :active_tags, -> { where(tags: { discarded_at: nil }) },
+           through: :post_tags,
+           source: :tag
 
   has_many :user_post_views, dependent: :delete_all
   has_many :post_similarities, dependent: :delete_all