Fix newly added reflection order when redefining association

Currently reflections keeps the order when first added even if when
redefining association. As a result of the order, redefining through
association which use newly added association will raise
`HasManyThroughOrderError`. We need to redefine reflection order as well
when redefining association.

Fixes #31068.

3 files changed, 5 insertions, 4 deletions

diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index a3f8bfd1f1..9e32b69786 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -34,7 +34,8 @@ module ActiveRecord
 
     def self.add_reflection(ar, name, reflection)
       ar.clear_reflections_cache
-      ar._reflections = ar._reflections.merge(name.to_s => reflection)
+      name = name.to_s
+      ar._reflections = ar._reflections.except(name).merge!(name => reflection)
     end
 
     def self.add_aggregate_reflection(ar, name, reflection)
diff --git a/activerecord/test/cases/associations/eager_test.rb b/activerecord/test/cases/associations/eager_test.rb
index 2649dc010f..9830917bc3 100644
--- a/activerecord/test/cases/associations/eager_test.rb
+++ b/activerecord/test/cases/associations/eager_test.rb
@@ -787,7 +787,7 @@ class EagerAssociationTest < ActiveRecord::TestCase
     Tagging.create!(taggable_type: "Post", taggable_id: post2.id, tag: tag)
 
     tag_with_includes = OrderedTag.includes(:tagged_posts).find(tag.id)
-    assert_equal(tag_with_includes.taggings.map(&:taggable).map(&:title), tag_with_includes.tagged_posts.map(&:title))
+    assert_equal tag_with_includes.ordered_taggings.map(&:taggable).map(&:title), tag_with_includes.tagged_posts.map(&:title)
   end
 
   def test_eager_has_many_through_multiple_with_order
diff --git a/activerecord/test/models/tag.rb b/activerecord/test/models/tag.rb
index bc13c3a42d..c1a8890a8a 100644
--- a/activerecord/test/models/tag.rb
+++ b/activerecord/test/models/tag.rb
@@ -11,6 +11,6 @@ end
 class OrderedTag < Tag
   self.table_name = "tags"
 
-  has_many :taggings, -> { order("taggings.id DESC") }, foreign_key: "tag_id"
-  has_many :tagged_posts, through: :taggings, source: "taggable", source_type: "Post"
+  has_many :ordered_taggings, -> { order("taggings.id DESC") }, foreign_key: "tag_id", class_name: "Tagging"
+  has_many :tagged_posts, through: :ordered_taggings, source: "taggable", source_type: "Post"
 end