Reduce db calls when presenting droplets

Eager load metadata, buildpack_lifecycle_buildpacks, and
buildpack_lifecycle_data.

Author: philippthun

app/controllers/v3/droplets_controller.rb

@@ -22,16 +22,16 @@ def index
     invalid_param!(message.errors.full_messages) unless message.valid?
 
     if app_nested?
-      app, dataset = DropletListFetcher.fetch_for_app(message)
+      app, dataset = DropletListFetcher.fetch_for_app(message, eager_loaded_associations: Presenters::V3::DropletPresenter.associated_resources)
       app_not_found! unless app && permission_queryer.can_read_from_space?(app.space.id, app.space.organization_id)
     elsif package_nested?
-      package, dataset = DropletListFetcher.fetch_for_package(message)
+      package, dataset = DropletListFetcher.fetch_for_package(message, eager_loaded_associations: Presenters::V3::DropletPresenter.associated_resources)
       package_not_found! unless package && permission_queryer.can_read_from_space?(package.space.id, package.space.organization_id)
     else
       dataset = if permission_queryer.can_read_globally?
-                  DropletListFetcher.fetch_all(message)
+                  DropletListFetcher.fetch_all(message, eager_loaded_associations: Presenters::V3::DropletPresenter.associated_resources)
                 else
-                  DropletListFetcher.fetch_for_spaces(message, permission_queryer.readable_space_guids)
+                  DropletListFetcher.fetch_for_spaces(message, permission_queryer.readable_space_guids, eager_loaded_associations: Presenters::V3::DropletPresenter.associated_resources)
                 end
     end
 

app/fetchers/droplet_list_fetcher.rb

@@ -3,32 +3,34 @@
 module VCAP::CloudController
   class DropletListFetcher < BaseListFetcher
     class << self
-      def fetch_all(message)
-        dataset = DropletModel.dataset
-        filter(message, nil, nil, dataset)
+      def fetch_all(message, eager_loaded_associations: [])
+        filter(message, nil, nil, droplet_dataset(eager_loaded_associations))
       end
 
-      def fetch_for_spaces(message, space_guids)
-        dataset = DropletModel.dataset
-        filter(message, nil, space_guids, dataset)
+      def fetch_for_spaces(message, space_guids, eager_loaded_associations: [])
+        filter(message, nil, space_guids, droplet_dataset(eager_loaded_associations))
       end
 
-      def fetch_for_app(message)
+      def fetch_for_app(message, eager_loaded_associations: [])
         app = AppModel.where(guid: message.app_guid).first
         return nil unless app
 
-        [app, filter(message, app, nil, app.droplets_dataset)]
+        [app, filter(message, app, nil, droplet_dataset(eager_loaded_associations, app.droplets_dataset))]
       end
 
-      def fetch_for_package(message)
+      def fetch_for_package(message, eager_loaded_associations: [])
         package = PackageModel.where(guid: message.package_guid).first
         return nil unless package
 
-        [package, filter(message, nil, nil, package.droplets_dataset)]
+        [package, filter(message, nil, nil, droplet_dataset(eager_loaded_associations, package.droplets_dataset))]
       end
 
       private
 
+      def droplet_dataset(eager_loaded_associations, dataset=DropletModel.dataset)
+        dataset.eager(eager_loaded_associations)
+      end
+
       def filter(message, app, space_guids, dataset)
         if message.requested?(:current) && app
           dataset = dataset.extension(:null_dataset)

app/presenters/v3/droplet_presenter.rb

@@ -7,6 +7,13 @@ module V3
       class DropletPresenter < BasePresenter
         include VCAP::CloudController::Presenters::Mixins::MetadataPresentationHelpers
 
+        class << self
+          # :labels and :annotations come from MetadataPresentationHelpers
+          def associated_resources
+            super + [{ buildpack_lifecycle_data: :buildpack_lifecycle_buildpacks }]
+          end
+        end
+
         def to_hash
           {
             guid: droplet.guid,

spec/request/droplets_spec.rb

@@ -607,6 +607,21 @@
       droplet2.buildpack_lifecycle_data.update(buildpacks: ['http://buildpack.git.url.com'], stack: 'stack-2')
     end
 
+    context 'eager loading' do
+      let(:get_droplets) { -> { get '/v3/droplets', nil, developer_headers } }
+
+      it 'eager loads associated data needed to present droplets' do
+        expect { get_droplets.call }.to have_queried_db_times(/SELECT .* FROM .droplets. /i, 1)
+        expect(last_response.status).to eq(200)
+        expect(parsed_response['resources'].count).to eq(2)
+
+        expect { get_droplets.call }.to have_queried_db_times(/SELECT .* FROM .droplet_annotations. /i, 1) # instead of 2 w/o eager loading
+        expect { get_droplets.call }.to have_queried_db_times(/SELECT .* FROM .droplet_labels. /i, 1) # instead of 2 w/o eager loading
+        expect { get_droplets.call }.to have_queried_db_times(/SELECT .* FROM .buildpack_lifecycle_buildpacks. /i, 1) # instead of 2 w/o eager loading
+        expect { get_droplets.call }.to have_queried_db_times(/SELECT .* FROM .buildpack_lifecycle_data. /i, 1) # instead of 2 w/o eager loading
+      end
+    end
+
     it_behaves_like 'list query endpoint' do
       let(:request) { 'v3/droplets' }
       let(:message) { VCAP::CloudController::DropletsListMessage }