Add and test preloading scope

2 files changed, 10 insertions, 1 deletions

diff --git a/lib/active_storage/attached/macros.rb b/lib/active_storage/attached/macros.rb
index 0452089a5f..5915793f8a 100644
--- a/lib/active_storage/attached/macros.rb
+++ b/lib/active_storage/attached/macros.rb
@@ -33,6 +33,10 @@ module ActiveStorage::Attached::Macros
   # There are no columns defined on the model side, Active Storage takes
   # care of the mapping between your records and the attachments.
   #
+  # To avoid N+1 queries, you can include the attached blobs in your query like so:
+  #
+  #   Gallery.where(user: Current.user).with_attached_photos
+  #
   # If the +:dependent+ option isn't set, all the attachments will be purged
   # (i.e. destroyed) whenever the record is destroyed.
   def has_many_attached(name, dependent: :purge_later)
@@ -44,6 +48,8 @@ module ActiveStorage::Attached::Macros
     has_many :"#{name}_attachments", -> { where(name: name) }, as: :record, class_name: "ActiveStorage::Attachment"
     has_many :"#{name}_blobs", through: :"#{name}_attachments"
 
+    scope :"with_attached_#{name}", -> { includes("#{name}_attachments": :blob) }
+
     if dependent == :purge_later
       before_destroy { public_send(name).purge_later }
     end
diff --git a/test/models/attachments_test.rb b/test/models/attachments_test.rb
index 45f62b0bbf..eac3cbe680 100644
--- a/test/models/attachments_test.rb
+++ b/test/models/attachments_test.rb
@@ -73,7 +73,10 @@ class ActiveStorage::AttachmentsTest < ActiveSupport::TestCase
       { io: StringIO.new("STUFF"), filename: "town.jpg", content_type: "image/jpg" },
       { io: StringIO.new("IT"), filename: "country.jpg", content_type: "image/jpg" })
 
-    User.where(id: @user.id).includes(highlights_attachments: :blob).first
+    highlights = User.where(id: @user.id).with_attached_highlights.first.highlights
+
+    assert_equal "town.jpg", highlights.first.filename.to_s
+    assert_equal "country.jpg", highlights.second.filename.to_s
   end
 
   test "purge attached blobs" do