Avoid N+1 SQL queries with CanCanCan accessibility checks

app/controllers/packages_controller.rb

@@ -288,6 +288,7 @@ class PackagesController < ApplicationController
   
   # Return packages matching the criteria given by parameters
   def query_packages
+    # Eager load the screenshots to avoid N+1 queries to check Screenshot.accessibly_by later
     packages = Package.includes(:screenshots).order(visits: :desc)
   
     # text search
@@ -298,7 +299,8 @@ class PackagesController < ApplicationController
     
     case params[:show]
     when 'with'
-      packages = packages.with_screenshots
+      # Enrich the result with the screenshots readable by the current user (CanCanCan)
+      packages = packages.where(screenshots: Screenshot.accessible_by(current_ability, :view))
       logger.debug 'Limiting packages to those with screenshots'
     when 'without'
       packages = packages.without_screenshots

app/controllers/welcome_controller.rb

@@ -1,7 +1,7 @@
 class WelcomeController < ApplicationController
   def home
     # TODO: Only approved screenshots!
-    @newest_upload = Screenshot.newest_upload
+    @newest_upload = Screenshot.newest.accessible_by(current_ability, :view).first
 
     @most_popular_package = Package.with_screenshots.order(visits: :desc).first
 

app/models/package.rb

@@ -48,7 +48,7 @@ class Package < ApplicationRecord
   def self.with_screenshots
     # Query for all packages who's ID appears in a screenshot's "package_id" field
     subselect = Screenshot.select(:package_id)
-    where(id: subselect )
+    where(id: subselect)
   end
 
   # Return a list of packages that have screenshots to be moderated
@@ -71,7 +71,7 @@ class Package < ApplicationRecord
 
   # Return a query of all approved/public screenshots of this package
   def screenshots_pending
-    self.screenshots.where('approved=false')
+    self.screenshots.where(approved: false)
   end
 
   # Return a list of packages that have unapproved screenshots

app/models/screenshot.rb

@@ -63,9 +63,9 @@ class Screenshot < ApplicationRecord
     self.save!
   end
 
-  # Get the newest screenshot regardless of the package it belongs to
+  # Get the newest screenshots regardless of the package it belongs to
-  def self.newest_upload
+  def self.newest
-    self.order(created_at: :desc).where(approved: true).first
+    self.order(created_at: :desc)
   end
 
   # Return the part of the version up to the first - or +

app/views/packages/browse.slim

@@ -18,7 +18,7 @@
             .cell.pkgcard data-equalizer-watch=true
               a.black href=package_path(name: pkg.name)
                 .image
-                  = small_img(pkg.screenshots.accessible_by(current_ability, :view).first, cls: '')
+                  = small_img(pkg.screenshots.first, cls: '')
                 .text.pkgname
                   = pkg.name
                 .text
@@ -29,7 +29,7 @@
             .small-12.medium-4.cell.pkgcard
               a.black href=package_path(name: pkg.name)
                 .image
-                  = small_img(pkg.screenshots.accessible_by(current_ability, :view).first, cls: '')
+                  = small_img(pkg.screenshots.first, cls: '')
             .small-12.medium-8.cell
               h2
                 a href=package_path(name: pkg.name)

app/views/packages/details.slim

@@ -25,7 +25,7 @@
                   .text
                     = screenshot.caption
                   // Has the unmoderated screenshot been uploaded by the current user?
-                  - if current_user.screenshots.include?(screenshot)
+                  - if current_user && current_user.screenshots.include?(screenshot)
                     .text
                       span.label.secondary
                         ' Uploaded by you