Remove remaining N+1 queries in merge requests API with emojis and labels

app/controllers/concerns/issuable_collections.rb

 module IssuableCollections
   extend ActiveSupport::Concern
   include SortingHelper
+  include Gitlab::IssuableMetadata
 
   included do
     helper_method :issues_finder
@@ -9,39 +10,6 @@ module IssuableCollections
 
   private
 
-  def issuable_meta_data(issuable_collection, collection_type)
-    # map has to be used here since using pluck or select will
-    # throw an error when ordering issuables by priority which inserts
-    # a new order into the collection.
-    # We cannot use reorder to not mess up the paginated collection.
-    issuable_ids = issuable_collection.map(&:id)
-
-    return {} if issuable_ids.empty?
-
-    issuable_note_count = Note.count_for_collection(issuable_ids, @collection_type)
-    issuable_votes_count = AwardEmoji.votes_for_collection(issuable_ids, @collection_type)
-    issuable_merge_requests_count =
-      if collection_type == 'Issue'
-        MergeRequestsClosingIssues.count_for_collection(issuable_ids)
-      else
-        []
-      end
-
-    issuable_ids.each_with_object({}) do |id, issuable_meta|
-      downvotes = issuable_votes_count.find { |votes| votes.awardable_id == id && votes.downvote? }
-      upvotes = issuable_votes_count.find { |votes| votes.awardable_id == id && votes.upvote? }
-      notes = issuable_note_count.find { |notes| notes.noteable_id == id }
-      merge_requests = issuable_merge_requests_count.find { |mr| mr.first == id }
-
-      issuable_meta[id] = Issuable::IssuableMeta.new(
-        upvotes.try(:count).to_i,
-        downvotes.try(:count).to_i,
-        notes.try(:count).to_i,
-        merge_requests.try(:last).to_i
-      )
-    end
-  end
-
   def issues_collection
     issues_finder.execute.preload(:project, :author, :assignees, :labels, :milestone, project: :namespace)
   end

changelogs/unreleased/sh-optimize-mr-api-emojis-and-labels.yml

+---
+title: Remove remaining N+1 queries in merge requests API with emojis and labels
+merge_request:
+author:

lib/api/entities.rb

@@ -316,10 +316,26 @@ module API
 
     class MergeRequestBasic < ProjectEntity
       expose :target_branch, :source_branch
-      expose :upvotes, :downvotes
+      expose :upvotes do |merge_request, options|
+        if options[:issuable_metadata]
+          options[:issuable_metadata][merge_request.id].upvotes
+        else
+          merge_request.upvotes
+        end
+      end
+      expose :downvotes do |merge_request, options|
+        if options[:issuable_metadata]
+          options[:issuable_metadata][merge_request.id].downvotes
+        else
+          merge_request.downvotes
+        end
+      end
       expose :author, :assignee, using: Entities::UserBasic
       expose :source_project_id, :target_project_id
-      expose :label_names, as: :labels
+      expose :labels do |merge_request, options|
+        # Avoids an N+1 query since labels are preloaded
+        merge_request.labels.map(&:title).sort
+      end
       expose :work_in_progress?, as: :work_in_progress
       expose :milestone, using: Entities::Milestone
       expose :merge_when_pipeline_succeeds

lib/api/merge_requests.rb

@@ -10,6 +10,8 @@ module API
     resource :projects, requirements: { id: %r{[^/]+} } do
       include TimeTrackingEndpoints
 
+      helpers ::Gitlab::IssuableMetadata
+
       helpers do
         def handle_merge_request_errors!(errors)
           if errors[:project_access].any?
@@ -42,8 +44,7 @@ module API
           args[:label_name] = args.delete(:labels)
 
           merge_requests = MergeRequestsFinder.new(current_user, args).execute
-                             .inc_notes_with_associations
-                             .preload(:target_project, :author, :assignee, :milestone, :merge_request_diff)
+                             .preload(:notes, :target_project, :author, :assignee, :milestone, :merge_request_diff, :labels)
 
           merge_requests.reorder(args[:order_by] => args[:sort])
         end
@@ -82,8 +83,9 @@ module API
         authorize! :read_merge_request, user_project
 
         merge_requests = find_merge_requests(project_id: user_project.id)
+        issuable_metadata = issuable_meta_data(merge_requests, 'MergeRequest')
 
-        present paginate(merge_requests), with: Entities::MergeRequestBasic, current_user: current_user, project: user_project
+        present paginate(merge_requests), with: Entities::MergeRequestBasic, current_user: current_user, project: user_project, issuable_metadata: issuable_metadata
       end
 
       desc 'Create a merge request' do

lib/gitlab/issuable_metadata.rb

+module Gitlab
+  module IssuableMetadata
+    def issuable_meta_data(issuable_collection, collection_type)
+      # map has to be used here since using pluck or select will
+      # throw an error when ordering issuables by priority which inserts
+      # a new order into the collection.
+      # We cannot use reorder to not mess up the paginated collection.
+      issuable_ids = issuable_collection.map(&:id)
+
+      return {} if issuable_ids.empty?
+
+      issuable_note_count = ::Note.count_for_collection(issuable_ids, collection_type)
+      issuable_votes_count = ::AwardEmoji.votes_for_collection(issuable_ids, collection_type)
+      issuable_merge_requests_count =
+        if collection_type == 'Issue'
+          ::MergeRequestsClosingIssues.count_for_collection(issuable_ids)
+        else
+          []
+        end
+
+      issuable_ids.each_with_object({}) do |id, issuable_meta|
+        downvotes = issuable_votes_count.find { |votes| votes.awardable_id == id && votes.downvote? }
+        upvotes = issuable_votes_count.find { |votes| votes.awardable_id == id && votes.upvote? }
+        notes = issuable_note_count.find { |notes| notes.noteable_id == id }
+        merge_requests = issuable_merge_requests_count.find { |mr| mr.first == id }
+
+        issuable_meta[id] = ::Issuable::IssuableMeta.new(
+          upvotes.try(:count).to_i,
+          downvotes.try(:count).to_i,
+          notes.try(:count).to_i,
+          merge_requests.try(:last).to_i
+        )
+      end
+    end
+  end
+end

spec/requests/api/merge_requests_spec.rb

@@ -16,7 +16,11 @@ describe API::MergeRequests do
   let!(:label) do
     create(:label, title: 'label', color: '#FFAABB', project: project)
   end
+  let!(:label2) { create(:label, title: 'a-test', color: '#FFFFFF', project: project) }
   let!(:label_link) { create(:label_link, label: label, target: merge_request) }
+  let!(:label_link2) { create(:label_link, label: label2, target: merge_request) }
+  let!(:downvote) { create(:award_emoji, :downvote, awardable: merge_request) }
+  let!(:upvote) { create(:award_emoji, :upvote, awardable: merge_request) }
 
   before do
     project.team << [user, :reporter]
@@ -44,6 +48,9 @@ describe API::MergeRequests do
         expect(json_response.last['sha']).to eq(merge_request.diff_head_sha)
         expect(json_response.last['merge_commit_sha']).to be_nil
         expect(json_response.last['merge_commit_sha']).to eq(merge_request.merge_commit_sha)
+        expect(json_response.last['downvotes']).to eq(1)
+        expect(json_response.last['upvotes']).to eq(1)
+        expect(json_response.last['labels']).to eq([label2.title, label.title])
         expect(json_response.first['title']).to eq(merge_request_merged.title)
         expect(json_response.first['sha']).to eq(merge_request_merged.diff_head_sha)
         expect(json_response.first['merge_commit_sha']).not_to be_nil
@@ -145,7 +152,7 @@ describe API::MergeRequests do
         expect(response).to have_http_status(200)
         expect(json_response).to be_an Array
         expect(json_response.length).to eq(1)
-        expect(json_response.first['labels']).to eq([label.title])
+        expect(json_response.first['labels']).to eq([label2.title, label.title])
       end
 
       it 'returns an array of labeled merge requests where all labels match' do
@@ -236,8 +243,8 @@ describe API::MergeRequests do
       expect(json_response['author']).to be_a Hash
       expect(json_response['target_branch']).to eq(merge_request.target_branch)
       expect(json_response['source_branch']).to eq(merge_request.source_branch)
-      expect(json_response['upvotes']).to eq(0)
-      expect(json_response['downvotes']).to eq(0)
+      expect(json_response['upvotes']).to eq(1)
+      expect(json_response['downvotes']).to eq(1)
       expect(json_response['source_project_id']).to eq(merge_request.source_project.id)
       expect(json_response['target_project_id']).to eq(merge_request.target_project.id)
       expect(json_response['work_in_progress']).to be_falsy