Make CollectionAssociation first/last with integer fetch with query

When first or last is called with an integer on an unloaded association,
the entire collection is loaded. This differs surprisingly from the
behavior of Relation#first/last, which translate the call into a limit
query. For large collections this can make a big difference in
performance.

Change CollectionAssociation#fetch_first_or_last_using_find? to make
this kind of call delegate to Relation.

1 files changed, 1 insertions, 3 deletions

diff --git a/activerecord/lib/active_record/associations/collection_association.rb b/activerecord/lib/active_record/associations/collection_association.rb
index 228c500f0a..0c326ed747 100644
--- a/activerecord/lib/active_record/associations/collection_association.rb
+++ b/activerecord/lib/active_record/associations/collection_association.rb
@@ -528,15 +528,13 @@ module ActiveRecord
         #   * target already loaded
         #   * owner is new record
         #   * target contains new or changed record(s)
-        #   * the first arg is an integer (which indicates the number of records to be returned)
         def fetch_first_or_last_using_find?(args)
           if args.first.is_a?(Hash)
             true
           else
             !(loaded? ||
               owner.new_record? ||
-              target.any? { |record| record.new_record? || record.changed? } ||
-              args.first.kind_of?(Integer))
+              target.any? { |record| record.new_record? || record.changed? })
           end
         end