fix merge conflict with actionpack changelog

1 files changed, 6 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/association_preload.rb b/activerecord/lib/active_record/association_preload.rb
index 3e7c787dee..da4ebdef51 100644
--- a/activerecord/lib/active_record/association_preload.rb
+++ b/activerecord/lib/active_record/association_preload.rb
@@ -65,7 +65,13 @@ module ActiveRecord
       end
 
       def set_association_single_records(id_to_record_map, reflection_name, associated_records, key)
+        seen_keys = {}
         associated_records.each do |associated_record|
+          #this is a has_one or belongs_to: there should only be one record.
+          #Unfortunately we can't (in portable way) ask the database for 'all records where foo_id in (x,y,z), but please
+          # only one row per distinct foo_id' so this where we enforce that
+          next if seen_keys[associated_record[key].to_s]
+          seen_keys[associated_record[key].to_s] = true
           mapped_records = id_to_record_map[associated_record[key].to_s]
           mapped_records.each do |mapped_record|
             mapped_record.send("set_#{reflection_name}_target", associated_record)
@@ -122,7 +128,6 @@ module ActiveRecord
         else
           records.each {|record| record.send("set_#{reflection.name}_target", nil)}
 
-
           set_association_single_records(id_to_record_map, reflection.name, find_associated_records(ids, reflection, preload_options), reflection.primary_key_name)
         end
       end