Cache assigned open issue count. Closes #18035

app/models/user.rb

@@ -782,6 +782,12 @@ class User < ActiveRecord::Base
     end
   end
 
+  def assigned_open_issues_count
+    Rails.cache.fetch(['users', id, 'assigned_open_issues_count'], expires_in: 60) do
+      assigned_issues.opened.count
+    end
+  end
+
   private
 
   def projects_union

app/views/layouts/nav/_dashboard.html.haml

@@ -30,7 +30,7 @@
       = icon('exclamation-circle fw')
       %span
         Issues
-        %span.count= number_with_delimiter(current_user.assigned_issues.opened.count)
+        %span.count= number_with_delimiter(current_user.assigned_open_issues_count)
   = nav_link(path: 'dashboard#merge_requests') do
     = link_to assigned_mrs_dashboard_path, title: 'Merge Requests', class: 'dashboard-shortcuts-merge_requests' do
       = icon('tasks fw')