Merge branch 'n-plus-one-notification-recipients' into 'master'

Fix some N+1s when calculating notification recipients

Closes #45534

See merge request gitlab-org/gitlab-ce!19535

app/models/notification_recipient.rb

@@ -64,7 +64,7 @@ class NotificationRecipient
     return false unless @target
     return false unless @target.respond_to?(:subscriptions)
 
-    subscription = @target.subscriptions.find_by_user_id(@user.id)
+    subscription = @target.subscriptions.find { |subscription| subscription.user_id == @user.id }
     subscription && !subscription.subscribed
   end
 

app/models/user.rb

@@ -1038,7 +1038,10 @@ class User < ActiveRecord::Base
 
   def notification_settings_for(source)
     if notification_settings.loaded?
-      notification_settings.find { |notification| notification.source == source }
+      notification_settings.find do |notification|
+        notification.source_type == source.class.base_class.name &&
+          notification.source_id == source.id
+      end
     else
       notification_settings.find_or_initialize_by(source: source)
     end

changelogs/unreleased/n-plus-one-notification-recipients.yml

+---
+title: Fix some sources of excessive query counts when calculating notification recipients
+merge_request:
+author:
+type: performance

spec/services/notification_recipient_service_spec.rb

+require 'spec_helper'
+
+describe NotificationRecipientService do
+  let(:service) { described_class }
+  let(:assignee) { create(:user) }
+  let(:project) { create(:project, :public) }
+  let(:other_projects) { create_list(:project, 5, :public) }
+
+  describe '#build_new_note_recipients' do
+    let(:issue) { create(:issue, project: project, assignees: [assignee]) }
+    let(:note) { create(:note_on_issue, noteable: issue, project_id: issue.project_id) }
+
+    def create_watcher
+      watcher = create(:user)
+      create(:notification_setting, project: project, user: watcher, level: :watch)
+
+      other_projects.each do |other_project|
+        create(:notification_setting, project: other_project, user: watcher, level: :watch)
+      end
+    end
+
+    it 'avoids N+1 queries' do
+      create_watcher
+
+      service.build_new_note_recipients(note)
+
+      control_count = ActiveRecord::QueryRecorder.new do
+        service.build_new_note_recipients(note)
+      end
+
+      create_watcher
+
+      expect { service.build_new_note_recipients(note) }.not_to exceed_query_limit(control_count)
+    end
+  end
+end