Merge branch 'sh-fix-pipeline-jobs-nplus-one' into 'master'

Eliminate N+1 queries for CI job artifacts in /api/projects/:id/pipelines/:pipeline_id/jobs

See merge request gitlab-org/gitlab-ce!19353

changelogs/unreleased/sh-fix-pipeline-jobs-nplus-one.yml

+---
+title: Eliminate N+1 queries for CI job artifacts in /api/prjoects/:id/pipelines/:pipeline_id/jobs
+merge_request:
+author:
+type: performance

lib/api/jobs.rb

@@ -54,6 +54,7 @@ module API
         pipeline = user_project.pipelines.find(params[:pipeline_id])
         builds = pipeline.builds
         builds = filter_builds(builds, params[:scope])
+        builds = builds.preload(:job_artifacts_archive)
 
         present paginate(builds), with: Entities::Job
       end

spec/requests/api/jobs_spec.rb

@@ -177,6 +177,18 @@ describe API::Jobs do
           json_response.each { |job| expect(job['pipeline']['id']).to eq(pipeline.id) }
         end
       end
+
+      it 'avoids N+1 queries' do
+        control_count = ActiveRecord::QueryRecorder.new(skip_cached: false) do
+          get api("/projects/#{project.id}/pipelines/#{pipeline.id}/jobs", api_user), query
+        end.count
+
+        3.times { create(:ci_build, :artifacts, pipeline: pipeline) }
+
+        expect do
+          get api("/projects/#{project.id}/pipelines/#{pipeline.id}/jobs", api_user), query
+        end.not_to exceed_all_query_limit(control_count)
+      end
     end
 
     context 'unauthorized user' do