Remove duplicated queries

app/views/shared/milestones/_issuable.html.haml

 -# @project is present when viewing Project's milestone
 - project = @project || issuable.project
 - namespace = @project_namespace || project.namespace.becomes(Namespace)
+- labels = issuable.labels
 - assignees = issuable.assignees
-- issuable_type = issuable.class.table_name
 - base_url_args = [namespace, project]
-- issuable_type_args = base_url_args + [issuable_type]
+- issuable_type_args = base_url_args + [issuable.class.table_name]
 - issuable_url_args = base_url_args + [issuable]
 
 %li.issuable-row
@@ -20,7 +20,7 @@
     = link_to [namespace, project, issuable] do
       %span.issuable-number= issuable.to_reference
 
-    - issuable.labels.each do |label|
+    - labels.each do |label|
       = link_to polymorphic_path(issuable_type_args, { milestone_title: @milestone.title, label_name: label.title, state: 'all' }) do
         - render_colored_label(label)
 

app/views/shared/milestones/_tabs.html.haml

+- issues_accessible = milestone.is_a?(GlobalMilestone) || can?(current_user, :read_issue, @project)
+
 .scrolling-tabs-container.inner-page-scroll-tabs.is-smaller
   .fade-left= icon('angle-left')
   .fade-right= icon('angle-right')
   %ul.nav-links.scrolling-tabs.js-milestone-tabs
-    - if milestone.is_a?(GlobalMilestone) || can?(current_user, :read_issue, @project)
+    - if issues_accessible
       %li.active
         = link_to '#tab-issues', 'data-toggle' => 'tab', 'data-show' => '.tab-issues-buttons' do
           Issues
@@ -25,13 +27,14 @@
         Labels
         %span.badge= milestone.labels.count
 
+- issues = milestone.sorted_issues(current_user)
 - show_project_name = local_assigns.fetch(:show_project_name, false)
 - show_full_project_name = local_assigns.fetch(:show_full_project_name, false)
 
 .tab-content.milestone-content
-  - if milestone.is_a?(GlobalMilestone) || can?(current_user, :read_issue, @project)
+  - if issues_accessible
     .tab-pane.active#tab-issues{ data: { sort_endpoint: (sort_issues_project_milestone_path(@project, @milestone) if @project && current_user) } }
-      = render 'shared/milestones/issues_tab', issues: milestone.sorted_issues(current_user), show_project_name: show_project_name, show_full_project_name: show_full_project_name
+      = render 'shared/milestones/issues_tab', issues: issues, show_project_name: show_project_name, show_full_project_name: show_full_project_name
     .tab-pane#tab-merge-requests
       -# loaded async
       = render "shared/milestones/tab_loading"

changelogs/unreleased/34736-n-1-problem-on-milestone-page.yml

+---
+title: N+1 problems on milestone page
+merge_request: 12670
+author: Takuya Noguchi