Reduce N+1 queries for Search API projects scope

Add new scope for Project model to preload data for
API entities. The scope will be used by the Search
API to preload data when returning Elastic Search
results.

Added tests for projects scope to avoid N+1 issues.
Reorganize merge_requests scope tests.

app/models/project.rb

@@ -506,6 +506,10 @@ class Project < ApplicationRecord
     left_outer_joins(:pages_metadatum)
       .where(project_pages_metadata: { project_id: nil })
   end
+  scope :with_api_entity_associations, -> {
+    preload(:project_feature, :route, :tags,
+            group: :ip_restrictions, namespace: [:route, :owner])
+  }
 
   enum auto_cancel_pending_pipelines: { disabled: 0, enabled: 1 }
 

ee/changelogs/unreleased/215707-improve-performance-of-search-api-advanced-projects-scope.yml

+---
+title: Fix N+1 queries for Elastic Search projects scope.
+merge_request: 32688
+author:
+type: performance

ee/spec/requests/api/search_spec.rb

@@ -68,6 +68,8 @@ describe API::Search do
         ensure_elasticsearch_index!
       end
 
+      it_behaves_like 'pagination', scope: 'merge_requests'
+
       it 'avoids N+1 queries' do
         control = ActiveRecord::QueryRecorder.new { get api(endpoint, user), params: { scope: 'merge_requests', search: '*' } }
 
@@ -176,17 +178,6 @@ describe API::Search do
       it_behaves_like 'pagination', scope: 'issues'
     end
 
-    context 'for merge_requests scope', :sidekiq_inline do
-      before do
-        create(:merge_request, target_branch: 'feature_2', source_project: project)
-        create(:merge_request, target_branch: 'feature_3', source_project: project)
-
-        ensure_elasticsearch_index!
-      end
-
-      it_behaves_like 'pagination', scope: 'merge_requests'
-    end
-
     unless level == :project
       context 'for projects scope', :sidekiq_inline do
         before do
@@ -197,6 +188,17 @@ describe API::Search do
         end
 
         it_behaves_like 'pagination', scope: 'projects'
+
+        it 'avoids N+1 queries' do
+          control = ActiveRecord::QueryRecorder.new { get api(endpoint, user), params: { scope: 'projects', search: '*' } }
+          create_list(:project, 3, :public, group: group)
+          create_list(:project, 4, :public)
+
+          ensure_elasticsearch_index!
+
+          # Some N+1 queries still exist
+          expect { get api(endpoint, user), params: { scope: 'projects', search: '*' } }.not_to exceed_query_limit(control.count + 4)
+        end
       end
     end
 

lib/api/search.rb

@@ -21,7 +21,8 @@ module API
       }.freeze
 
       SCOPE_PRELOAD_METHOD = {
-          merge_requests: :with_api_entity_associations
+          merge_requests: :with_api_entity_associations,
+          projects: :with_api_entity_associations
       }.freeze
 
       def search(additional_params = {})