Fix #45339 attachments for new record within transaction

Co-authored-by: Juan Eduardo Roig <jeroig@gmail.com>

activestorage/lib/active_storage/attached/many.rb

@@ -47,16 +47,9 @@ def blobs
     #   document.images.attach(io: File.open("/path/to/racecar.jpg"), filename: "racecar.jpg", content_type: "image/jpeg")
     #   document.images.attach([ first_blob, second_blob ])
     def attach(*attachables)
-      if record.persisted? && !record.changed?
-        record.public_send("#{name}=", blobs + attachables.flatten)
-        if record.save
-          record.public_send("#{name}")
-        else
-          false
-        end
-      else
-        record.public_send("#{name}=", (change&.attachables || blobs) + attachables.flatten)
-      end
+      record.public_send("#{name}=", blobs + attachables.flatten)
+      return false if record.persisted? && !record.changed? && !record.save
+      record.public_send("#{name}")
     end
 
     # Returns true if any attachments have been made.

activestorage/test/models/attached/many_test.rb

@@ -181,6 +181,19 @@ class ActiveStorage::ManyAttachedTest < ActiveSupport::TestCase
     assert ActiveStorage::Blob.service.exist?(@user.highlights.third.key)
   end
 
+  test "attaching many new blobs within a transaction on a new record uploads all the files" do
+    user = User.create!(name: "John") do |user|
+      user.highlights.attach(io: StringIO.new("STUFF"), filename: "funky.jpg", content_type: "image/jpeg")
+      user.highlights.attach(io: StringIO.new("THINGS"), filename: "town.jpg", content_type: "image/jpeg")
+    end
+
+    assert_equal 2, user.highlights.count
+    assert_equal "funky.jpg", user.highlights.first.filename.to_s
+    assert_equal "town.jpg", user.highlights.second.filename.to_s
+    assert ActiveStorage::Blob.service.exist?(user.highlights.first.key)
+    assert ActiveStorage::Blob.service.exist?(user.highlights.second.key)
+  end
+
   test "attaching new blobs within a transaction create the exact amount of records" do
     assert_difference -> { ActiveStorage::Blob.count }, +2 do
       ActiveRecord::Base.transaction do