Restore some unrelated changes from d9cb907c

app/views/search/results/_issue.html.haml

 .search-result-row
   %h4
     = confidential_icon(issue)
-    = link_to [issue.project.namespace.becomes(Namespace), issue.project, issue] do
+    = link_to namespace_project_issue_path(issue.project.namespace.becomes(Namespace), issue.project, issue) do
       %span.term.str-truncated= issue.title
     - if issue.closed?
       %span.badge.badge-danger.prepend-left-5= _("Closed")

app/views/search/results/_merge_request.html.haml

 .search-result-row
   %h4
-    = link_to [merge_request.target_project.namespace.becomes(Namespace), merge_request.target_project, merge_request] do
+    = link_to namespace_project_merge_request_path(merge_request.target_project.namespace.becomes(Namespace), merge_request.target_project, merge_request) do
       %span.term.str-truncated= merge_request.title
     - if merge_request.merged?
       %span.badge.badge-primary.prepend-left-5= _("Merged")

app/views/search/results/_milestone.html.haml

 .search-result-row
   %h4
-    = link_to [milestone.project.namespace.becomes(Namespace), milestone.project, milestone] do
+    = link_to namespace_project_milestone_path(milestone.project.namespace.becomes(Namespace), milestone.project, milestone) do
       %span.term.str-truncated= milestone.title
 
   - if milestone.description.present?

ee/app/models/concerns/elastic/milestones_search.rb

@@ -12,7 +12,7 @@ module Elastic
         # https://gitlab.com/gitlab-org/gitlab-ee/issues/349
         data = {}
 
-        [:id, :title, :description, :project_id, :created_at, :updated_at].each do |attr|
+        [:id, :iid, :title, :description, :project_id, :created_at, :updated_at].each do |attr|
           data[attr.to_s] = safely_read_attribute_for_elasticsearch(attr)
         end
 

ee/changelogs/unreleased/10854-elasticsearch_avoid_db.yml

+---
+title: Avoid loading database objects for Elasticsearch results
+merge_request: 12691
+author:
+type: performance

ee/spec/features/search/elastic/global_search_spec.rb

 require 'spec_helper'
 
-describe 'Global elastic search' do
+describe 'Global elastic search', :elastic do
   let(:user) { create(:user) }
   let(:project) { create(:project, :repository, :wiki_repo, namespace: user.namespace) }
 
   before do
     stub_ee_application_setting(elasticsearch_search: true, elasticsearch_indexing: true)
-    Gitlab::Elastic::Helper.create_empty_index
 
     project.add_maintainer(user)
     sign_in(user)
   end
 
   after do
-    Gitlab::Elastic::Helper.delete_index
     stub_ee_application_setting(elasticsearch_search: false, elasticsearch_indexing: false)
   end
 
+  shared_examples 'a pure Elasticsearch result' do
+    it 'avoids N+1 database queries' do
+      create(object, creation_args)
+      Gitlab::Elastic::Helper.refresh_index
+
+      control_count = ActiveRecord::QueryRecorder.new { visit path }.count
+
+      create_list(object, 10, creation_args)
+      Gitlab::Elastic::Helper.refresh_index
+
+      control_count = control_count + (10 * query_count_multiplier) + 1
+
+      expect { visit path }.not_to exceed_query_limit(control_count)
+    end
+  end
+
+  describe 'I do not overload the database' do
+    context 'searching issues' do
+      let(:object) { :issue }
+      let(:creation_args) { { project: project, title: 'initial' } }
+      let(:path) { search_path(search: 'initial', scope: 'issues') }
+      let(:query_count_multiplier) { 0 }
+
+      it_behaves_like 'a pure Elasticsearch result'
+    end
+
+    context 'searching projects' do
+      let(:object) { :project }
+      let(:creation_args) { { namespace: user.namespace } }
+      let(:path) { search_path(search: 'project*', scope: 'projects') }
+      # Each Project requires 4 extra queries: one for each "count" (forks, open MRs, open Issues) and one for access level
+      let(:query_count_multiplier) { 4 }
+
+      it_behaves_like 'a pure Elasticsearch result'
+    end
+
+    context 'searching merge requests' do
+      it 'avoids N+1 database queries' do
+        path = search_path(search: 'initial', scope: 'merge_requests')
+
+        create(:merge_request, title: 'initial', source_project: project)
+        Gitlab::Elastic::Helper.refresh_index
+
+        control_count = ActiveRecord::QueryRecorder.new { visit path }.count
+
+        merge_requests = create_list(:merge_request, 10, title: 'initial')
+        merge_requests.each { |mr| mr.target_project.add_maintainer(user) }
+        Gitlab::Elastic::Helper.refresh_index
+
+        # Each MR loaded has a Route load that has been tricky to track down
+        expect { visit path }.not_to exceed_query_limit(control_count + 11)
+      end
+    end
+
+    context 'searching milestones' do
+      let(:object) { :milestone }
+      let(:creation_args) { { project: project } }
+      let(:path) { search_path(search: 'milestone*', scope: 'milestones') }
+      let(:query_count_multiplier) { 0 }
+
+      it_behaves_like 'a pure Elasticsearch result'
+    end
+  end
+
   describe 'I search through the issues and I see pagination' do
     before do
       create_list(:issue, 21, project: project, title: 'initial')

ee/spec/models/concerns/elastic/milestone_spec.rb

@@ -39,6 +39,7 @@ describe Milestone, :elastic do
 
     expected_hash = milestone.attributes.extract!(
       'id',
+      'iid',
       'title',
       'description',
       'project_id',