grab attachments from correct shard for submission downloads

closes #ADMIN-2751

Change-Id: Ic78a59b5a5cc0b8bae11c19e2b2188d99664db5f
Reviewed-on: https://gerrit.instructure.com/200859
Tested-by: Jenkins
Reviewed-by: Mysti Lilla <mysti@instructure.com>
QA-Review: James Williams <jamesw@instructure.com>
Product-Review: James Williams <jamesw@instructure.com>

app/models/exporters/submission_exporter.rb

@@ -29,7 +29,7 @@ module Exporters
             # they do not include submissions for group assignments for anyone
             # but the original submitter of the group submission
             attachment_ids = submission.attachment_ids.try(:split, ",")
-            attachments = attachment_ids.present? ? Attachment.where(id: attachment_ids) : []
+            attachments = attachment_ids.present? ? main_sub.shard.activate { Attachment.where(id: attachment_ids) } : []
             attachments.each do |attachment|
               # TODO handle missing attachments
               path = File.join(base_path, attachment.display_name)
@@ -47,4 +47,4 @@ module Exporters
       end
     end
   end
-end
+end

lib/content_zipper.rb

@@ -446,7 +446,7 @@ class ContentZipper
     # they do not include submissions for group assignments for anyone
     # but the original submitter of the group submission
     attachment_ids = submission.attachment_ids.try(:split, ",")
-    Attachment.where(id: Array.wrap(attachment_ids))
+    submission.shard.activate { Attachment.where(id: Array.wrap(attachment_ids)) }
   end
 
   def get_user_name(students, submission)