Merge branch 'jprovazn-csv' into 'master'

Use 'preload' in export to CSV

Closes #4376

See merge request gitlab-org/gitlab-ee!3841

changelogs/unreleased-ee/3841-fix-export-to-csv.yml

+---
+title: Fix export to CSV if a filter with multiple labels is used
+merge_request:
+author:
+type: fixed

ee/app/services/issues/export_csv_service.rb

@@ -21,7 +21,7 @@ module Issues
 
     def csv_builder
       @csv_builder ||=
-        CsvBuilder.new(@issues.includes(:author, :assignees, :timelogs), header_to_value_hash)
+        CsvBuilder.new(@issues.preload(:author, :assignees, :timelogs), header_to_value_hash)
     end
 
     private

spec/services/issues/export_csv_service_spec.rb

@@ -127,6 +127,20 @@ describe Issues::ExportCsvService do
       expect(csv[0]['Time Spent']).to eq '560'
       expect(csv[1]['Time Spent']).to eq '0'
     end
+
+    context 'with issues filtered by labels and project' do
+      let(:subject) do
+        described_class.new(
+          IssuesFinder.new(user,
+                           project_id: project.id,
+                           label_name: %w(Idea Feature)).execute)
+      end
+
+      it 'returns only filtered objects' do
+        expect(csv.count).to eq(1)
+        expect(csv[0]['Issue ID']).to eq issue.iid.to_s
+      end
+    end
   end
 
   context 'with minimal details' do