Exclude coverage data from the pipelines page

When displaying a project's pipelines
(Projects::PipelinesController#index) we now exclude the coverage data.
This data was not used by the frontend, yet getting it would require one
SQL query per pipeline. These queries in turn could be quite expensive
on GitLab.com.

4 files changed, 19 insertions, 2 deletions

diff --git a/app/controllers/projects/pipelines_controller.rb b/app/controllers/projects/pipelines_controller.rb
index 91afe24b707..6b40fc2fe68 100644
--- a/app/controllers/projects/pipelines_controller.rb
+++ b/app/controllers/projects/pipelines_controller.rb
@@ -34,7 +34,7 @@ class Projects::PipelinesController < Projects::ApplicationController
           pipelines: PipelineSerializer
             .new(project: @project, current_user: @current_user)
             .with_pagination(request, response)
-            .represent(@pipelines),
+            .represent(@pipelines, disable_coverage: true),
           count: {
             all: @pipelines_count,
             running: @running_count,
diff --git a/app/serializers/pipeline_entity.rb b/app/serializers/pipeline_entity.rb
index 6457294b285..f782b411b84 100644
--- a/app/serializers/pipeline_entity.rb
+++ b/app/serializers/pipeline_entity.rb
@@ -4,7 +4,11 @@ class PipelineEntity < Grape::Entity
   expose :id
   expose :user, using: UserEntity
   expose :active?, as: :active
-  expose :coverage
+
+  # Coverage isn't always necessary (e.g. when displaying project pipelines in
+  # the UI). Instead of creating an entirely different entity we just allow the
+  # disabling of this specific field whenever necessary.
+  expose :coverage, unless: proc { options[:disable_coverage] }
   expose :source
 
   expose :created_at, :updated_at
diff --git a/spec/controllers/projects/pipelines_controller_spec.rb b/spec/controllers/projects/pipelines_controller_spec.rb
index c22e455ea2d..9e7bc20a6d1 100644
--- a/spec/controllers/projects/pipelines_controller_spec.rb
+++ b/spec/controllers/projects/pipelines_controller_spec.rb
@@ -41,6 +41,12 @@ describe Projects::PipelinesController do
       expect(json_response['count']['finished']).to eq '1'
     end
 
+    it 'does not include coverage data for the pipelines' do
+      subject
+
+      expect(json_response['pipelines'][0]).not_to include('coverage')
+    end
+
     context 'when performing gitaly calls', :request_store do
       it 'limits the Gitaly requests' do
         expect { subject }.to change { Gitlab::GitalyClient.get_request_count }.by(3)
diff --git a/spec/serializers/pipeline_entity_spec.rb b/spec/serializers/pipeline_entity_spec.rb
index 2473c561f4b..e67d12b7a89 100644
--- a/spec/serializers/pipeline_entity_spec.rb
+++ b/spec/serializers/pipeline_entity_spec.rb
@@ -26,6 +26,13 @@ describe PipelineEntity do
         expect(subject).to include :updated_at, :created_at
       end
 
+      it 'excludes coverage data when disabled' do
+        entity = described_class
+          .represent(pipeline, request: request, disable_coverage: true)
+
+        expect(entity.as_json).not_to include(:coverage)
+      end
+
       it 'contains details' do
         expect(subject).to include :details
         expect(subject[:details])