Merge pull request rails#45244 from luanzeba/association_size_on_scop…

…ed_relations

Clear out target when no new records

(cherry picked from commit 5fae32e)

activerecord/lib/active_record/associations/has_many_association.rb

@@ -79,10 +79,13 @@ def count_records
             scope.count(:all)
           end
 
-          # If there's nothing in the database and @target has no new records
-          # we are certain the current target is an empty array. This is a
-          # documented side-effect of the method that may avoid an extra SELECT.
-          loaded! if count == 0
+          # If there's nothing in the database, @target should only contain new
+          # records or be an empty array. This is a documented side-effect of
+          # the method that may avoid an extra SELECT.
+          if count == 0
+            target.select!(&:new_record?)
+            loaded!
+          end
 
           [association_scope.limit_value, count].compact.min
         end

activerecord/test/cases/associations_test.rb

@@ -299,6 +299,20 @@ def test_target_merging_ignores_persisted_in_memory_records
     assert_equal 1, david.thinking_posts.size
     assert_equal 1, david.thinking_posts.to_a.size
   end
+
+  def test_size_differentiates_between_new_and_persisted_in_memory_records_when_loaded_records_are_empty
+    member = members(:blarpy_winkup)
+    assert_empty member.favorite_memberships
+
+    membership = member.favorite_memberships.create!
+    membership.update!(favorite: false)
+
+    # CollectionAssociation#size has different behavior when loaded vs. non-loaded
+    # the first call will mark the association as loaded and the second call will
+    # take a different code path, so it's important to keep both assertions
+    assert_equal 0, member.favorite_memberships.size
+    assert_equal 0, member.favorite_memberships.size
+  end
 end
 
 class OverridingAssociationsTest < ActiveRecord::TestCase