Clear offset cache on CollectionProxy reset/reload

The `@offsets` cache is used by FinderMethods to cache records found by
find_nth. This cache is cleared in AR::Relation#reset, but not in
CollectionProxy#reset or CollectionProxy#reload.

Because of this, since #29098, calling #first/#find_nth/etc after
calling #reload or #reset on an association could return a stale record.
This is an issue both when the full association target is loaded and
when the item is loaded in #find_nth.

This commit solves the problem by clearing the `@offsets` cache in
CollectionProxy#reset and CollectionProxy#reload.

2 files changed, 28 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/associations/collection_proxy.rb b/activerecord/lib/active_record/associations/collection_proxy.rb
index 8cdb508c43..88b05bbcfa 100644
--- a/activerecord/lib/active_record/associations/collection_proxy.rb
+++ b/activerecord/lib/active_record/associations/collection_proxy.rb
@@ -1088,6 +1088,7 @@ module ActiveRecord
       #   # => [#<Pet id: 1, name: "Snoop", group: "dogs", person_id: 1>]
       def reload
         proxy_association.reload
+        @offsets = {}
         reset_scope
       end
 
@@ -1110,6 +1111,7 @@ module ActiveRecord
       def reset
         proxy_association.reset
         proxy_association.reset_scope
+        @offsets = {}
         reset_scope
       end
 
diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index 590d3642bd..ae58dbff21 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -741,6 +741,32 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal client2, firm.clients.merge!(where: ["#{QUOTED_TYPE} = :type", { type: "Client" }], order: "id").first
   end
 
+  def test_find_first_after_reset
+    firm = Firm.all.merge!(order: "id").first
+
+    # Calling first twice should return the same object
+    original_object_id = firm.clients.first.object_id
+    assert_equal firm.clients.first.object_id, original_object_id, "Expected multiple invocations of #first to return the same object"
+
+    firm.clients.reset
+
+    # It should return a different object, since the association has been reloaded
+    assert_not_equal original_object_id, firm.clients.first.object_id, "Expected #first after #reload to return a new object"
+  end
+
+  def test_find_first_after_reload
+    firm = Firm.all.merge!(order: "id").first
+
+    # Calling first twice should return the same object
+    original_object_id = firm.clients.first.object_id
+    assert_equal firm.clients.first.object_id, original_object_id, "Expected multiple invocations of #first to return the same object"
+
+    firm.clients.reload
+
+    # It should return a different object, since the association has been reloaded
+    assert_not_equal original_object_id, firm.clients.first.object_id, "Expected #first after #reload to return a new object"
+  end
+
   def test_find_all_with_include_and_conditions
     assert_nothing_raised do
       Developer.all.merge!(joins: :audit_logs, where: { "audit_logs.message" => nil, :name => "Smith" }).to_a