Resolve new N+1 by adding preloads and metadata to issues end points

lib/api/entities.rb

@@ -320,7 +320,10 @@ module API
     end
 
     class IssueBasic < ProjectEntity
-      expose :label_names, as: :labels
+      expose :labels do |issue, options|
+        # Avoids an N+1 query since labels are preloaded
+        issue.labels.map(&:title).sort
+      end
       expose :milestone, using: Entities::Milestone
       expose :assignees, :author, using: Entities::UserBasic
 
@@ -329,7 +332,22 @@ module API
       end
 
       expose :user_notes_count
-      expose :upvotes, :downvotes
+      expose :upvotes do |issue, options|
+        if options[:issuable_metadata]
+          # Avoids an N+1 query when metadata is included
+          options[:issuable_metadata][issue.id].upvotes
+        else
+          issue.upvotes
+        end
+      end
+      expose :downvotes do |issue, options|
+        if options[:issuable_metadata]
+          # Avoids an N+1 query when metadata is included
+          options[:issuable_metadata][issue.id].downvotes
+        else
+          issue.downvotes
+        end
+      end
       expose :due_date
       expose :confidential
 

lib/api/issues.rb

@@ -4,6 +4,8 @@ module API
 
     before { authenticate! }
 
+    helpers ::Gitlab::IssuableMetadata
+
     helpers do
       def find_issues(args = {})
         args = params.merge(args)
@@ -13,6 +15,7 @@ module API
         args[:label_name] = args.delete(:labels)
 
         issues = IssuesFinder.new(current_user, args).execute
+          .preload(:assignees, :labels, :notes)
 
         issues.reorder(args[:order_by] => args[:sort])
       end
@@ -65,7 +68,11 @@ module API
       get do
         issues = find_issues
 
-        present paginate(issues), with: Entities::IssueBasic, current_user: current_user
+        options = { with: Entities::IssueBasic,
+                    current_user: current_user }
+        options[:issuable_metadata] = issuable_meta_data(issues, 'Issue')
+
+        present paginate(issues), options
       end
     end
 
@@ -86,7 +93,11 @@ module API
 
         issues = find_issues(group_id: group.id)
 
-        present paginate(issues), with: Entities::IssueBasic, current_user: current_user
+        options = { with: Entities::IssueBasic,
+                    current_user: current_user }
+        options[:issuable_metadata] = issuable_meta_data(issues, 'Issue')
+
+        present paginate(issues), options
       end
     end
 
@@ -109,7 +120,12 @@ module API
 
         issues = find_issues(project_id: project.id)
 
-        present paginate(issues), with: Entities::IssueBasic, current_user: current_user, project: user_project
+        options = { with: Entities::IssueBasic,
+                    current_user: current_user,
+                    project: user_project }
+        options[:issuable_metadata] = issuable_meta_data(issues, 'Issue')
+
+        present paginate(issues), options
       end
 
       desc 'Get a single project issue' do