Merge pull request rails#46579 from joshuay03/fix-through-association-incorrect-preloading

Fix: Incorrectly preloading through association records when middle association has been loaded

Author: byroot

activerecord/lib/active_record/associations/preloader/through_association.rb

@@ -74,7 +74,7 @@ def source_preloaders
           end
 
           def middle_records
-            through_preloaders.flat_map(&:preloaded_records)
+            through_records_by_owner.values.flatten
           end
 
           def through_preloaders

activerecord/test/cases/associations_test.rb

@@ -37,6 +37,8 @@
 require "models/sharded/blog"
 require "models/sharded/blog_post"
 require "models/sharded/comment"
+require "models/member_detail"
+require "models/organization"
 
 
 class AssociationsTest < ActiveRecord::TestCase
@@ -539,8 +541,8 @@ def test_associations_raise_with_name_error_if_associated_to_classes_that_do_not
 end
 
 class PreloaderTest < ActiveRecord::TestCase
-  fixtures :posts, :comments, :books, :authors, :tags, :taggings, :essays, :categories,
-    :author_addresses, :sharded_blog_posts, :sharded_comments
+  fixtures :posts, :comments, :books, :authors, :tags, :taggings, :essays, :categories, :author_addresses,
+           :sharded_blog_posts, :sharded_comments, :members, :member_details, :organizations
 
   def test_preload_with_scope
     post = posts(:welcome)
@@ -629,6 +631,21 @@ def test_preload_grouped_queries_of_through_records
     end
   end
 
+  def test_preload_through_records_with_already_loaded_middle_record
+    member = members(:groucho)
+    expected_member_detail_ids = member.organization_member_details_2.pluck(:id)
+
+    member.reload.organization # load through record
+
+    assert_queries(1) do
+      ActiveRecord::Associations::Preloader.new(records: [member], associations: :organization_member_details_2).call
+    end
+
+    assert_no_queries do
+      assert_equal expected_member_detail_ids.sort, member.organization_member_details_2.map(&:id).sort
+    end
+  end
+
   def test_preload_with_instance_dependent_scope
     david = authors(:david)
     david2 = Author.create!(name: "David")