Merge branch 'dm-discussions-n-plus-1' into 'master'

Resolve N+1 query issue with discussions

Closes #33013

See merge request !11775

app/models/concerns/noteable.rb

@@ -43,7 +43,12 @@ module Noteable
   end
 
   def resolvable_discussions
-    @resolvable_discussions ||= discussion_notes.resolvable.discussions(self)
+    @resolvable_discussions ||=
+      if defined?(@discussions)
+        @discussions.select(&:resolvable?)
+      else
+        discussion_notes.resolvable.discussions(self)
+      end
   end
 
   def discussions_resolvable?

app/models/discussion.rb

@@ -21,7 +21,8 @@ class Discussion
   end
 
   def self.build_collection(notes, context_noteable = nil)
-    notes.group_by { |n| n.discussion_id(context_noteable) }.values.map { |notes| build(notes, context_noteable) }
+    grouped_notes = notes.group_by { |n| n.discussion_id(context_noteable) }
+    grouped_notes.values.map { |notes| build(notes, context_noteable) }
   end
 
   # Returns an alphanumeric discussion ID based on `build_discussion_id`

app/models/note.rb

@@ -110,7 +110,7 @@ class Note < ActiveRecord::Base
     end
 
     def discussions(context_noteable = nil)
-      Discussion.build_collection(fresh, context_noteable)
+      Discussion.build_collection(all.includes(:noteable).fresh, context_noteable)
     end
 
     def find_discussion(discussion_id)

changelogs/unreleased/dm-discussions-n-plus-1.yml

@@ -0,0 +1,4 @@
+---
+title: Resolve N+1 query issue with discussions
+merge_request:
+author:

config/initializers/active_record_preloader.rb

@@ -0,0 +1,15 @@
+module ActiveRecord
+  module Associations
+    class Preloader
+      module NoCommitPreloader
+        def preloader_for(reflection, owners, rhs_klass)
+          return NullPreloader if rhs_klass == ::Commit
+
+          super
+        end
+      end
+
+      prepend NoCommitPreloader
+    end
+  end
+end