Optimize queries for snippet listings

- Avoid N+1 queries for authors and comment counts
- Avoid an additional snippet existence query

9 files changed, 49 insertions, 28 deletions

diff --git a/app/controllers/dashboard/snippets_controller.rb b/app/controllers/dashboard/snippets_controller.rb
index 161c22046f9..382f54c6c00 100644
--- a/app/controllers/dashboard/snippets_controller.rb
+++ b/app/controllers/dashboard/snippets_controller.rb
@@ -1,14 +1,16 @@
 # frozen_string_literal: true
 
 class Dashboard::SnippetsController < Dashboard::ApplicationController
+  include Gitlab::NoteableMetadata
+
   skip_cross_project_access_check :index
 
   def index
-    @snippets = SnippetsFinder.new(
-      current_user,
-      author: current_user,
-      scope: params[:scope]
-    ).execute
-    @snippets = @snippets.page(params[:page])
+    @snippets = SnippetsFinder.new(current_user, author: current_user, scope: params[:scope])
+      .execute
+      .page(params[:page])
+      .inc_author
+
+    @noteable_meta_data = noteable_meta_data(@snippets, 'Snippet')
   end
 end
diff --git a/app/controllers/explore/snippets_controller.rb b/app/controllers/explore/snippets_controller.rb
index 76ed142c939..6192b594593 100644
--- a/app/controllers/explore/snippets_controller.rb
+++ b/app/controllers/explore/snippets_controller.rb
@@ -1,8 +1,14 @@
 # frozen_string_literal: true
 
 class Explore::SnippetsController < Explore::ApplicationController
+  include Gitlab::NoteableMetadata
+
   def index
-    @snippets = SnippetsFinder.new(current_user).execute
-    @snippets = @snippets.page(params[:page])
+    @snippets = SnippetsFinder.new(current_user)
+      .execute
+      .page(params[:page])
+      .inc_author
+
+    @noteable_meta_data = noteable_meta_data(@snippets, 'Snippet')
   end
 end
diff --git a/app/controllers/projects/snippets_controller.rb b/app/controllers/projects/snippets_controller.rb
index 59f948959d6..c84e9fbc2d7 100644
--- a/app/controllers/projects/snippets_controller.rb
+++ b/app/controllers/projects/snippets_controller.rb
@@ -6,6 +6,7 @@ class Projects::SnippetsController < Projects::ApplicationController
   include SpammableActions
   include SnippetsActions
   include RendersBlob
+  include Gitlab::NoteableMetadata
 
   skip_before_action :verify_authenticity_token,
     if: -> { action_name == 'show' && js_request? }
@@ -28,15 +29,16 @@ class Projects::SnippetsController < Projects::ApplicationController
   respond_to :html
 
   def index
-    @snippets = SnippetsFinder.new(
-      current_user,
-      project: @project,
-      scope: params[:scope]
-    ).execute
-    @snippets = @snippets.page(params[:page])
+    @snippets = SnippetsFinder.new(current_user, project: @project, scope: params[:scope])
+      .execute
+      .page(params[:page])
+      .inc_author
+
     if @snippets.out_of_range? && @snippets.total_pages != 0
-      redirect_to project_snippets_path(@project, page: @snippets.total_pages)
+      return redirect_to project_snippets_path(@project, page: @snippets.total_pages)
     end
+
+    @noteable_meta_data = noteable_meta_data(@snippets, 'Snippet')
   end
 
   def new
diff --git a/app/controllers/snippets_controller.rb b/app/controllers/snippets_controller.rb
index 869655e9550..c1e05b72b37 100644
--- a/app/controllers/snippets_controller.rb
+++ b/app/controllers/snippets_controller.rb
@@ -7,6 +7,7 @@ class SnippetsController < ApplicationController
   include SnippetsActions
   include RendersBlob
   include PreviewMarkdown
+  include Gitlab::NoteableMetadata
 
   skip_before_action :verify_authenticity_token,
     if: -> { action_name == 'show' && js_request? }
@@ -32,7 +33,11 @@ class SnippetsController < ApplicationController
       @user = UserFinder.new(params[:username]).find_by_username!
 
       @snippets = SnippetsFinder.new(current_user, author: @user, scope: params[:scope])
-        .execute.page(params[:page])
+        .execute
+        .page(params[:page])
+        .inc_author
+
+      @noteable_meta_data = noteable_meta_data(@snippets, 'Snippet')
 
       render 'index'
     else
diff --git a/app/controllers/users_controller.rb b/app/controllers/users_controller.rb
index 91e0efcf45f..e38d4073de3 100644
--- a/app/controllers/users_controller.rb
+++ b/app/controllers/users_controller.rb
@@ -4,6 +4,7 @@ class UsersController < ApplicationController
   include RoutableActions
   include RendersMemberAccess
   include ControllerWithCrossProjectAccessCheck
+  include Gitlab::NoteableMetadata
 
   requires_cross_project_access show: false,
                                 groups: false,
@@ -165,11 +166,12 @@ class UsersController < ApplicationController
   end
 
   def load_snippets
-    @snippets = SnippetsFinder.new(
-      current_user,
-      author: user,
-      scope: params[:scope]
-    ).execute.page(params[:page])
+    @snippets = SnippetsFinder.new(current_user, author: user, scope: params[:scope])
+      .execute
+      .page(params[:page])
+      .inc_author
+
+    @noteable_meta_data = noteable_meta_data(@snippets, 'Snippet')
   end
 
   def build_canonical_path(user)
diff --git a/app/models/concerns/noteable.rb b/app/models/concerns/noteable.rb
index 6a44bc7c401..b3e4df730b4 100644
--- a/app/models/concerns/noteable.rb
+++ b/app/models/concerns/noteable.rb
@@ -3,6 +3,10 @@
 module Noteable
   extend ActiveSupport::Concern
 
+  # This object is used to gather noteable meta data for list displays
+  # avoiding n+1 queries and improving performance.
+  NoteableMeta = Struct.new(:user_notes_count)
+
   class_methods do
     # `Noteable` class names that support replying to individual notes.
     def replyable_types
diff --git a/app/models/snippet.rb b/app/models/snippet.rb
index 00931457344..b2fca65b9e0 100644
--- a/app/models/snippet.rb
+++ b/app/models/snippet.rb
@@ -55,6 +55,7 @@ class Snippet < ApplicationRecord
   scope :are_public, -> { where(visibility_level: Snippet::PUBLIC) }
   scope :public_and_internal, -> { where(visibility_level: [Snippet::PUBLIC, Snippet::INTERNAL]) }
   scope :fresh, -> { order("created_at DESC") }
+  scope :inc_author, -> { includes(:author) }
   scope :inc_relations_for_view, -> { includes(author: :status) }
 
   participant :author
diff --git a/app/views/shared/snippets/_list.html.haml b/app/views/shared/snippets/_list.html.haml
index 5d2152eb411..766f48fff3d 100644
--- a/app/views/shared/snippets/_list.html.haml
+++ b/app/views/shared/snippets/_list.html.haml
@@ -1,12 +1,11 @@
 - remote = local_assigns.fetch(:remote, false)
 - link_project = local_assigns.fetch(:link_project, false)
 
-- if @snippets.exists?
+- if @snippets.to_a.empty?
+  .nothing-here-block= s_("SnippetsEmptyState|No snippets found")
+- else
   .snippets-list-holder
     %ul.content-list
       = render partial: 'shared/snippets/snippet', collection: @snippets, locals: { link_project: link_project }
 
     = paginate @snippets, theme: 'gitlab', remote: remote
-
-- else
-  .nothing-here-block= s_("SnippetsEmptyState|No snippets found")
diff --git a/app/views/shared/snippets/_snippet.html.haml b/app/views/shared/snippets/_snippet.html.haml
index 42af97bc6af..0ef626868a2 100644
--- a/app/views/shared/snippets/_snippet.html.haml
+++ b/app/views/shared/snippets/_snippet.html.haml
@@ -1,4 +1,5 @@
 - link_project = local_assigns.fetch(:link_project, false)
+- notes_count = @noteable_meta_data[snippet.id].user_notes_count
 
 %li.snippet-row
   = image_tag avatar_icon_for_user(snippet.author), class: "avatar s40 d-none d-sm-block", alt: ''
@@ -12,10 +13,9 @@
 
     %ul.controls
       %li
-        - note_count = snippet.notes.user.count
-        = link_to reliable_snippet_path(snippet, anchor: 'notes'), class: ('no-comments' if note_count.zero?) do
+        = link_to reliable_snippet_path(snippet, anchor: 'notes'), class: ('no-comments' if notes_count.zero?) do
           = icon('comments')
-          = note_count
+          = notes_count
       %li
         %span.sr-only
           = visibility_level_label(snippet.visibility_level)