PERF: reduce SQL queries by aggreating records

plugin.rb

@@ -6,6 +6,45 @@
 register_asset 'stylesheets/previews_common.scss'
 register_asset 'stylesheets/previews_mobile.scss'
 
+module TopicListAddon
+  def load_topics
+    @topics = super
+
+    # SQL only works with postgresql 9.4+
+    # TODO: better to keep track of previewed posts' id so they can be loaded at once
+    accepted_anwser_post_ids = @topics.map { |t| t.custom_fields["accepted_answer_post_id"]&.to_i }.compact
+    posts = Post.all.joins("JOIN unnest('{#{accepted_anwser_post_ids.join(',')}}'::int[]) WITH ORDINALITY t(id, ord) USING (id)").order("t.ord")
+    idx = 0
+    @topics.each do |t|
+      next unless t.custom_fields["accepted_answer_post_id"]
+      t.previewed_post = posts[idx]
+      idx += 1
+    end
+    normal_topic_ids = topics.delete_if { |t| t.custom_fields["accepted_answer_post_id"]&.to_i }.map(&:id)
+    posts = Post.where("post_number = 1 AND topic_id IN (?)", normal_topic_ids).joins("JOIN unnest('{#{normal_topic_ids.join(',')}}'::int[]) WITH ORDINALITY t(topic_id, ord) USING (topic_id)").order("t.ord")
+    idx = 0
+    @topics.each do |t|
+      next if t.custom_fields["accepted_answer_post_id"]
+      t.previewed_post = posts[idx]
+      idx += 1
+    end
+
+    if @current_user
+      previewed_post_ids = @topics.map { |t| t.previewed_post&.id }.compact
+      post_actions_map = {}
+      PostAction.where("post_id IN (?) AND user_id = ?", previewed_post_ids, @current_user.id).each do |pa|
+        (post_actions_map[pa.post_id] ||= []) << pa
+      end
+      @topics.each do |t|
+        next unless t.previewed_post
+        t.previewed_post_actions = post_actions_map[t.previewed_post.id]
+      end
+    end
+
+    @topics
+  end
+end
+
 after_initialize do
   Category.register_custom_field_type('topic_list_category_badge_move', :boolean)
   Topic.register_custom_field_type('thumbnails', :json)
@@ -45,6 +84,62 @@ def save_thumbnails(id, thumbnails)
     end
   end
 
+  class ::Topic
+    attr_accessor :previewed_post
+    attr_accessor :previewed_post_actions
+  end
+
+  require_dependency 'guardian/post_guardian'
+  module ::PostGuardian
+    def previewed_post_can_act?(post, topic, action_key, opts={})
+      taken = opts[:taken_actions].try(:keys).to_a
+      is_flag = PostActionType.is_flag?(action_key)
+      already_taken_this_action = taken.any? && taken.include?(PostActionType.types[action_key])
+      already_did_flagging      = taken.any? && (taken & PostActionType.flag_types.values).any?
+
+      result = if authenticated? && post && !@user.anonymous?
+
+        return false if action_key == :notify_moderators && !SiteSetting.enable_private_messages
+
+        # we allow flagging for trust level 1 and higher
+        # always allowed for private messages
+        (is_flag && not(already_did_flagging) && (@user.has_trust_level?(TrustLevel[1]) || topic.private_message?)) ||
+
+        # not a flagging action, and haven't done it already
+        not(is_flag || already_taken_this_action) &&
+
+        # nothing except flagging on archived topics
+        not(topic.try(:archived?)) &&
+
+        # nothing except flagging on deleted posts
+        not(post.trashed?) &&
+
+        # don't like your own stuff
+        not(action_key == :like && is_my_own?(post)) &&
+
+        # new users can't notify_user because they are not allowed to send private messages
+        not(action_key == :notify_user && !@user.has_trust_level?(SiteSetting.min_trust_to_send_messages)) &&
+
+        # non-staff can't send an official warning
+        not(action_key == :notify_user && !is_staff? && opts[:is_warning].present? && opts[:is_warning] == 'true') &&
+
+        # can't send private messages if they're disabled globally
+        not(action_key == :notify_user && !SiteSetting.enable_private_messages) &&
+
+        # no voting more than once on single vote topics
+        not(action_key == :vote && opts[:voted_in_topic] && topic.has_meta_data_boolean?(:single_vote))
+      end
+
+      !!result
+    end
+  end
+
+  TopicList.preloaded_custom_fields << "accepted_answer_post_id" if TopicList.respond_to? :preloaded_custom_fields
+  TopicList.preloaded_custom_fields << "thumbnails" if TopicList.respond_to? :preloaded_custom_fields
+  TopicList.class_eval do
+    prepend TopicListAddon
+  end
+
   require 'cooked_post_processor'
   class ::CookedPostProcessor
 
@@ -89,20 +184,17 @@ class ::TopicListItemSerializer
                :topic_post_bookmarked,
                :topic_post_is_current_users
 
-    def first_post_id
-     first = Post.find_by(topic_id: object.id, post_number: 1)
-     first ? first.id : false
+    def include_topic_post_id?
+      object.previewed_post.present?
     end
 
     def topic_post_id
-      accepted_id = object.custom_fields["accepted_answer_post_id"].to_i
-      return accepted_id > 0 ? accepted_id : first_post_id
+      object.previewed_post.id
     end
-    alias :include_topic_post_id? :first_post_id
 
     def excerpt
-      cooked = Post.where(id: topic_post_id).pluck('cooked')
-      excerpt = PrettyText.excerpt(cooked[0], SiteSetting.topic_list_excerpt_length, keep_emoji_images: true)
+      cooked = object.previewed_post.cooked
+      excerpt = PrettyText.excerpt(cooked, SiteSetting.topic_list_excerpt_length, keep_emoji_images: true)
       excerpt.gsub!(/(\[#{I18n.t 'excerpt_image'}\])/, "") if excerpt
       excerpt
     end
@@ -142,61 +234,51 @@ def get_thumbnails_from_image_url
     end
 
     def topic_post_actions
-      return [] if !scope.current_user
-      PostAction.where(post_id: topic_post_id, user_id: scope.current_user.id)
+      object.previewed_post_actions || []
     end
 
     def topic_like_action
       topic_post_actions.select {|a| a.post_action_type_id == PostActionType.types[:like]}
     end
 
-    def topic_post
-      Post.find(topic_post_id)
-    end
-
     def topic_post_bookmarked
       !!topic_post_actions.any?{|a| a.post_action_type_id == PostActionType.types[:bookmark]}
     end
-    alias :include_topic_post_bookmarked? :first_post_id
+    alias :include_topic_post_bookmarked? :topic_post_id
 
     def topic_post_liked
       topic_like_action.any?
     end
-    alias :include_topic_post_liked? :first_post_id
+    alias :include_topic_post_liked? :topic_post_id
 
     def topic_post_like_count
-      topic_post.like_count
+      object.previewed_post.like_count
     end
-    alias :include_topic_post_like_count? :first_post_id
 
     def include_topic_post_like_count?
-      first_post_id && topic_post_like_count > 0
+      object.previewed_post&.id && topic_post_like_count > 0
     end
 
     def topic_post_can_like
-      post = topic_post
       return false if !scope.current_user || topic_post_is_current_users
-      scope.post_can_act?(post, PostActionType.types[:like], taken_actions: topic_post_actions)
+      scope.previewed_post_can_act?(object.previewed_post, object, PostActionType.types[:like], taken_actions: topic_post_actions)
     end
-    alias :include_topic_post_can_like? :first_post_id
+    alias :include_topic_post_can_like? :topic_post_id
 
     def topic_post_is_current_users
-      return scope.current_user && (topic_post.user_id == scope.current_user.id)
+      return scope.current_user && (object.previewed_post.user_id == scope.current_user.id)
     end
-    alias :include_topic_post_is_current_users? :first_post_id
+    alias :include_topic_post_is_current_users? :topic_post_id
 
     def topic_post_can_unlike
       return false if !scope.current_user
       action = topic_like_action[0]
       !!(action && (action.user_id == scope.current_user.id) && (action.created_at > SiteSetting.post_undo_action_window_mins.minutes.ago))
     end
-    alias :include_topic_post_can_unlike? :first_post_id
+    alias :include_topic_post_can_unlike? :topic_post_id
 
   end
 
-  TopicList.preloaded_custom_fields << "accepted_answer_post_id" if TopicList.respond_to? :preloaded_custom_fields
-  TopicList.preloaded_custom_fields << "thumbnails" if TopicList.respond_to? :preloaded_custom_fields
-
   add_to_serializer(:basic_category, :topic_list_excerpt) {object.custom_fields["topic_list_excerpt"]}
   add_to_serializer(:basic_category, :topic_list_thumbnail) {object.custom_fields["topic_list_thumbnail"]}
   add_to_serializer(:basic_category, :topic_list_action) {object.custom_fields["topic_list_action"]}