fixes #2229

app/models/forum_topic.rb

@@ -96,7 +96,14 @@ class ForumTopic < ActiveRecord::Base
         ForumTopicVisit.create(:user_id => user.id, :forum_topic_id => id, :last_read_at => updated_at)
       end
 
-      # user.update_attribute(:last';¬≥÷_forum_read_at, ForumTopicVisit.where(:user_id => user.id, :forum_topic_id => id).minimum(:last_read_at) || updated_at)
+      has_unread_topics = ForumTopic.where("forum_topics.updated_at >= ?", user.last_forum_read_at)
+      .joins("left join forum_topic_visits on (forum_topic_visits.forum_topic_id = forum_topics.id and forum_topic_visits.user_id = #{user.id})")
+      .where("(forum_topic_visits.id is null or forum_topic_visits.last_read_at < forum_topics.updated_at)")
+      .exists?
+      unless has_unread_topics
+        user.update_attribute(:last_forum_read_at, Time.now)
+        ForumTopicVisit.prune!(user)
+      end
     end
   end
 

db/migrate/20150119191042_add_updated_at_index_to_forum_topics.rb

@@ -0,0 +1,11 @@
+class AddUpdatedAtIndexToForumTopics < ActiveRecord::Migration
+  def up
+    execute "set statement_timeout = 0"
+    add_index :forum_topics, :updated_at
+  end
+
+  def down
+    execute "set statement_timeout = 0"
+    remove_index :forum_topics, :updated_at
+  end
+end