Reuse the CollectionAssociation#reader proxy cache if the foreign key is present from the start.

When a new record has the necessary information prior to save, we can
avoid busting the cache.

We could simply clear the @proxy on #reset or #reset_scope, but that
would clear the cache more often than necessary.

1 files changed, 12 insertions, 0 deletions

diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index 675bed9bfa..290b2a0d6b 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -532,9 +532,21 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_update_all_on_association_accessed_before_save
     firm = Firm.new(name: 'Firm')
+    clients_proxy_id = firm.clients.object_id
     firm.clients << Client.first
     firm.save!
     assert_equal firm.clients.count, firm.clients.update_all(description: 'Great!')
+    assert_not_equal clients_proxy_id, firm.clients.object_id
+  end
+
+  def test_update_all_on_association_accessed_before_save_with_explicit_foreign_key
+    # We can use the same cached proxy object because the id is available for the scope
+    firm = Firm.new(name: 'Firm', id: 100)
+    clients_proxy_id = firm.clients.object_id
+    firm.clients << Client.first
+    firm.save!
+    assert_equal firm.clients.count, firm.clients.update_all(description: 'Great!')
+    assert_equal clients_proxy_id, firm.clients.object_id
   end
 
   def test_belongs_to_sanity