Delegate `only` query method to relation as with `except`

I've found the skewness of delegation methods between `except` and
`only` in a88b6f2.

The `only` method is closely similar with `except` as `SpawnMethods`.

https://github.com/rails/rails/blob/e056b9bfb07c4eb3bcc6672d885aadd72bec574f/activerecord/lib/active_record/relation/spawn_methods.rb#L53-L67

It is preferable both behaves the same way.

1 files changed, 4 insertions, 0 deletions

diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 85719cb8d0..36b4000018 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -1503,9 +1503,11 @@ class RelationTest < ActiveRecord::TestCase
 
     author_posts = relation.except(:order, :limit)
     assert_equal Post.where(author_id: 1).sort_by(&:id), author_posts.sort_by(&:id)
+    assert_equal author_posts.sort_by(&:id), relation.scoping { Post.except(:order, :limit).sort_by(&:id) }
 
     all_posts = relation.except(:where, :order, :limit)
     assert_equal Post.all.sort_by(&:id), all_posts.sort_by(&:id)
+    assert_equal all_posts.sort_by(&:id), relation.scoping { Post.except(:where, :order, :limit).sort_by(&:id) }
   end
 
   def test_only
@@ -1514,9 +1516,11 @@ class RelationTest < ActiveRecord::TestCase
 
     author_posts = relation.only(:where)
     assert_equal Post.where(author_id: 1).sort_by(&:id), author_posts.sort_by(&:id)
+    assert_equal author_posts.sort_by(&:id), relation.scoping { Post.only(:where).sort_by(&:id) }
 
     all_posts = relation.only(:order)
     assert_equal Post.order("id ASC").to_a, all_posts.to_a
+    assert_equal all_posts.to_a, relation.scoping { Post.only(:order).to_a }
   end
 
   def test_anonymous_extension