PERF: Improve topic serialization performance

plugin.rb

@@ -315,14 +315,18 @@
     updated_at
     visibility
   ]
-  activity_pub_post_custom_fields.each do |field_name|
-    register_post_custom_field_type("activity_pub_#{field_name.to_s}", :string)
+  activity_pub_post_custom_field_names =
+    activity_pub_post_custom_fields.map do |field_name|
+      "activity_pub_#{field_name.to_s}"
+    end
+  activity_pub_post_custom_field_names.each do |field_name|
+    register_post_custom_field_type(field_name, :string)
   end
 
   add_permitted_post_create_param(:activity_pub_visibility)
 
   add_to_class(:post, :activity_pub_url) do
-    self.activity_pub_object&.url
+    activity_pub_local? ?  activity_pub_full_url : activity_pub_object&.url
   end
   add_to_class(:post, :activity_pub_full_url) do
     "#{DiscourseActivityPub.base_url}#{self.url}"
@@ -375,9 +379,9 @@
   add_to_class(:post, :activity_pub_after_scheduled) do |args = {}|
     activity_pub_update_custom_fields(args)
   end
-  activity_pub_post_custom_fields.each do |field_name|
-    add_to_class(:post, "activity_pub_#{field_name}".to_sym) do
-      custom_fields["activity_pub_#{field_name}"]
+  activity_pub_post_custom_field_names.each do |field_name|
+    add_to_class(:post, field_name.to_sym) do
+      custom_fields[field_name]
     end
   end
   add_to_class(:post, :activity_pub_updated_at) do
@@ -404,8 +408,8 @@
       type: "post"
     }
 
-    activity_pub_post_custom_fields.each do |field_name|
-      model[field_name.to_sym] = self.send("activity_pub_#{field_name.to_s}")
+    activity_pub_post_custom_fields.each do |field|
+      model[field.to_sym] = self.send("activity_pub_#{field.to_s}")
     end
 
     group_ids =[
@@ -416,8 +420,8 @@
     MessageBus.publish("/activity-pub", { model: model }, { group_ids: group_ids })
   end
   add_to_class(:post, :before_clear_all_activity_pub_objects) do
-    activity_pub_post_custom_fields.each do |field_name|
-      self.custom_fields["activity_pub_#{field_name.to_s}"] = nil
+    activity_pub_post_custom_field_names.each do |field_name|
+      self.custom_fields[field_name] = nil
     end
     self.save_custom_fields(true)
   end
@@ -509,10 +513,12 @@
   add_to_serializer(:post, :activity_pub_enabled) do
     object.activity_pub_enabled
   end
-  activity_pub_post_custom_fields.each do |field_name|
-    add_to_serializer(:post, "activity_pub_#{field_name}".to_sym) do
-      object.send("activity_pub_#{field_name}")
-    end
+  activity_pub_post_custom_field_names.each do |field_name|
+    add_to_serializer(
+      :post,
+      field_name.to_sym,
+      include_condition: -> { object.activity_pub_enabled }
+    ) { object.send(field_name) }
   end
   add_to_serializer(
     :post,
@@ -545,6 +551,19 @@
     include_condition: -> { object.activity_pub_enabled }
   ) { object.activity_pub_is_first_post? }
 
+  TopicView.on_preload do |topic_view|
+    if topic_view.topic.activity_pub_enabled
+      Post.preload_custom_fields(
+        topic_view.posts,
+        activity_pub_post_custom_field_names
+      )
+      ActiveRecord::Associations::Preloader.new(
+        records: topic_view.posts,
+        associations: [:activity_pub_object]
+      ).call
+    end
+  end
+
   PostAction.include DiscourseActivityPub::AP::ModelCallbacks
 
   add_to_class(:post_action, :activity_pub_enabled) do

spec/requests/list_controller_spec.rb

@@ -0,0 +1,80 @@
+# frozen_string_literal: true
+
+RSpec.describe ListController do
+  describe "#index" do
+    context "with activity pub topics" do
+      fab!(:category1) { Fabricate(:category) }
+      fab!(:category2) { Fabricate(:category) }
+      fab!(:category3) { Fabricate(:category) }
+      fab!(:topic_ids) {
+        topic_ids = []
+        [category1, category2].each do |category|
+          5.times do
+            topic = Fabricate(:topic, category: category)
+            topic_ids << topic.id
+            collection = Fabricate(:discourse_activity_pub_ordered_collection, model: topic)
+            post = Fabricate(:post, topic: topic)
+            note = Fabricate(:discourse_activity_pub_object_note, model: post, collection_id: collection.id)
+            activity = Fabricate(:discourse_activity_pub_activity_create, object: note)
+          end
+        end
+        topic_ids
+      }
+
+      def track_index_queries
+        track_sql_queries do
+          get "/latest.json"
+          expect(response.status).to eq(200)
+          body = response.parsed_body
+          expect(body["topic_list"]["topics"].map { |t| t["id"] }).to contain_exactly(*topic_ids)
+        end
+      end
+
+      context "without a logged in user" do
+        it "does not increase the number of queries" do
+          SiteSetting.activity_pub_enabled = false
+
+          # prime caches
+          get "/latest.json"
+          expect(response.status).to eq(200)
+
+          disabled_queries = track_index_queries
+
+          SiteSetting.activity_pub_enabled = true
+          toggle_activity_pub(category1, callbacks: true)
+          toggle_activity_pub(category2, callbacks: true)
+
+          enabled_queries = track_index_queries
+
+          expect(enabled_queries.count).to eq(disabled_queries.count)
+        end
+      end
+
+      context "with a logged in user" do
+        let!(:user) { Fabricate(:user) }
+
+        before do
+          sign_in(user)
+        end
+
+        it "does not increase the number of queries" do
+          SiteSetting.activity_pub_enabled = false
+
+          # prime caches
+          get "/latest.json"
+          expect(response.status).to eq(200)
+
+          disabled_queries = track_index_queries
+
+          SiteSetting.activity_pub_enabled = true
+          toggle_activity_pub(category1, callbacks: true)
+          toggle_activity_pub(category2, callbacks: true)
+
+          enabled_queries = track_index_queries
+
+          expect(enabled_queries.count).to eq(disabled_queries.count)
+        end
+      end
+    end
+  end
+end

spec/requests/topics_controller_spec.rb

@@ -0,0 +1,107 @@
+# frozen_string_literal: true
+
+RSpec.describe TopicsController do
+  ADDITIONAL_QUERY_LIMIT = 6
+
+  describe "#show" do
+    fab!(:category) { Fabricate(:category) }
+    fab!(:topic) { Fabricate(:topic, category: category) }
+    fab!(:collection) { Fabricate(:discourse_activity_pub_ordered_collection, model: topic) }
+    fab!(:posts) {
+      posts = []
+      10.times do
+        post = Fabricate(:post, topic: topic)
+        posts << post
+        note = Fabricate(:discourse_activity_pub_object_note, model: post, collection_id: collection.id)
+        Fabricate(:discourse_activity_pub_activity_create, object: note)
+      end
+      posts
+    }
+
+    def track_topic_show_queries
+      track_sql_queries do
+        get "/t/#{topic.id}.json"
+        expect(response.status).to eq(200)
+      end
+    end
+
+    context "without a logged in user" do
+      context "with activity pub first_post enabled" do
+        it "does not increase the number of queries beyond the limit" do
+          SiteSetting.activity_pub_enabled = false
+
+          get "/t/#{topic.id}.json"
+          expect(response.status).to eq(200)
+
+          disabled_queries = track_topic_show_queries
+
+          SiteSetting.activity_pub_enabled = true
+          toggle_activity_pub(category, callbacks: true, publication_type: 'first_post')
+
+          enabled_queries = track_topic_show_queries
+          expect(enabled_queries.count).to be <= (disabled_queries.count + ADDITIONAL_QUERY_LIMIT)
+        end
+      end
+
+      context "with activity pub full_topic enabled" do
+        it "does not increase the number of queries beyond the limit" do
+          SiteSetting.activity_pub_enabled = false
+
+          get "/t/#{topic.id}.json"
+          expect(response.status).to eq(200)
+
+          disabled_queries = track_topic_show_queries
+
+          SiteSetting.activity_pub_enabled = true
+          toggle_activity_pub(category, callbacks: true, publication_type: 'full_topic')
+
+          enabled_queries = track_topic_show_queries
+          expect(enabled_queries.count).to be <= (disabled_queries.count + ADDITIONAL_QUERY_LIMIT)
+        end
+      end
+    end
+
+    context "with a logged in user" do
+      let!(:user) { Fabricate(:user) }
+
+      before do
+        sign_in(user)
+      end
+
+      context "with activity pub first_post enabled" do
+        it "does not increase the number of queries beyond the limit" do
+          SiteSetting.activity_pub_enabled = false
+
+          get "/t/#{topic.id}.json"
+          expect(response.status).to eq(200)
+
+          disabled_queries = track_topic_show_queries
+
+          SiteSetting.activity_pub_enabled = true
+          toggle_activity_pub(category, callbacks: true, publication_type: 'first_post')
+
+          enabled_queries = track_topic_show_queries
+
+          expect(enabled_queries.count).to be <= (disabled_queries.count + ADDITIONAL_QUERY_LIMIT)
+        end
+      end
+
+      context "with activity pub full_topic enabled" do
+        it "does not increase the number of queries beyond the limit" do
+          SiteSetting.activity_pub_enabled = false
+
+          get "/t/#{topic.id}.json"
+          expect(response.status).to eq(200)
+
+          disabled_queries = track_topic_show_queries
+
+          SiteSetting.activity_pub_enabled = true
+          toggle_activity_pub(category, callbacks: true, publication_type: 'full_topic')
+
+          enabled_queries = track_topic_show_queries
+          expect(enabled_queries.count).to be <= (disabled_queries.count + ADDITIONAL_QUERY_LIMIT)
+        end
+      end
+    end
+  end
+end