Merge branch 'performance-improve' into 'master'

More performance improvements for large groups

* fetch team members using much less sql queries
* collect mentioned users without iterating over all project users

app/models/concerns/mentionable.rb

@@ -50,7 +50,7 @@ module Mentionable
     matches.each do |match|
       identifier = match.delete "@"
       if has_project
-        id = project.team.members.find { |u| u.username == identifier }.try(:id)
+        id = project.team.members.find_by(username: identifier).try(:id)
       else
         id = User.where(username: identifier).pluck(:id).first
       end

app/models/project_team.rb

@@ -144,7 +144,10 @@ class ProjectTeam
       group_members = group_members.send(level) if group
     end
 
-    (project_members + group_members).map(&:user).uniq
+    user_ids = project_members.pluck(:user_id)
+    user_ids += group_members.pluck(:user_id) if group
+
+    User.where(id: user_ids)
   end
 
   def group