class TopicFeaturedUsers attr_reader :topic def initialize(topic) @topic = topic end def self.count 4 end # Chooses which topic users to feature def choose(args={}) self.class.ensure_consistency!(topic.id.to_i) update_participant_count end def user_ids [topic.featured_user1_id, topic.featured_user2_id, topic.featured_user3_id, topic.featured_user4_id].uniq.compact end def self.ensure_consistency!(topic_id=nil) sql = < t.user_id AND p.user_id <> t.last_post_user_id GROUP BY t.id, p.user_id ), cte2 as ( SELECT id, user_id, ROW_NUMBER() OVER(PARTITION BY id ORDER BY last_post_date ASC) as rank FROM cte WHERE rank <= #{count} ) UPDATE topics tt SET featured_user1_id = featured_user1, featured_user2_id = featured_user2, featured_user3_id = featured_user3, featured_user4_id = featured_user4 FROM ( SELECT c.id, MAX(case when c.rank = 1 then c.user_id end) featured_user1, MAX(case when c.rank = 2 then c.user_id end) featured_user2, MAX(case when c.rank = 3 then c.user_id end) featured_user3, MAX(case when c.rank = 4 then c.user_id end) featured_user4 FROM cte2 as c GROUP BY c.id ) x WHERE x.id = tt.id AND ( COALESCE(featured_user1_id,-99) <> COALESCE(featured_user1,-99) OR COALESCE(featured_user2_id,-99) <> COALESCE(featured_user2,-99) OR COALESCE(featured_user3_id,-99) <> COALESCE(featured_user3,-99) OR COALESCE(featured_user4_id,-99) <> COALESCE(featured_user4,-99) ) #{"AND x.id = #{topic_id.to_i}" if topic_id} SQL Topic.exec_sql(sql) end private def update_participant_count topic.update_columns(participant_count: topic.posts.count('distinct user_id')) end end