Merge pull request rails#50800 from Edouard-chin/ec-inverseof-blob

Fix ActiveStorage::Blob inverse association:

Author: byroot

activestorage/app/models/active_storage/attachment.rb

@@ -28,7 +28,7 @@ class ActiveStorage::Attachment < ActiveStorage::Record
   # :method:
   #
   # Returns the associated ActiveStorage::Blob.
-  belongs_to :blob, class_name: "ActiveStorage::Blob", autosave: true
+  belongs_to :blob, class_name: "ActiveStorage::Blob", autosave: true, inverse_of: :attachments
 
   delegate_missing_to :blob
   delegate :signed_id, to: :blob

activestorage/lib/active_storage/attached/changes/create_one_of_many.rb

@@ -4,7 +4,11 @@ module ActiveStorage
   class Attached::Changes::CreateOneOfMany < Attached::Changes::CreateOne # :nodoc:
     private
       def find_attachment
-        record.public_send("#{name}_attachments").detect { |attachment| attachment.blob_id == blob.id }
+        if blob.persisted?
+          record.public_send("#{name}_attachments").detect { |attachment| attachment.blob_id == blob.id }
+        else
+          blob.attachments.find { |attachment| attachment.record == record }
+        end
       end
   end
 end