Don't unset foreign key when preloading missing record

When a belongs to association's target is set, its foreign key is now
updated to match the new target. This is the correct behaviour when a
new record is assigned, but not when the existing record is preloaded.

As long as we mark the association as loaded, we can skip setting the
target when the record is missing and avoid clobbering the foreign key.

1 files changed, 2 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/associations/preloader/association.rb b/activerecord/lib/active_record/associations/preloader/association.rb
index 0f38d6bbda..d6f7359055 100644
--- a/activerecord/lib/active_record/associations/preloader/association.rb
+++ b/activerecord/lib/active_record/associations/preloader/association.rb
@@ -42,11 +42,11 @@ module ActiveRecord
 
           def associate_records_to_owner(owner, records)
             association = owner.association(reflection.name)
+            association.loaded!
             if reflection.collection?
-              association.loaded!
               association.target.concat(records)
             else
-              association.target = records.first
+              association.target = records.first unless records.empty?
             end
           end