Association creation and finding should work consistently (#32048)

This is an alternative of #29722, and revert of #29601 and a1fcbd9.

Currently, association creation and normal association finding doesn't
respect `store_full_sti_class`. But eager loading and preloading respect
the setting. This means that if set `store_full_sti_class = false`
(`true` by default), eager loading and preloading can not find
created polymorphic records.

Association creation and finding should work consistently.

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

@@ -117,7 +117,7 @@ module ActiveRecord
             scope = klass.scope_for_association
 
             if reflection.type
-              scope.where!(reflection.type => model.base_class.sti_name)
+              scope.where!(reflection.type => model.base_class.name)
             end
 
             scope.merge!(reflection_scope) if reflection.scope

activerecord/lib/active_record/reflection.rb

@@ -193,7 +193,7 @@ module ActiveRecord
         klass_scope       = klass_join_scope(table, predicate_builder)
 
         if type
-          klass_scope.where!(type => foreign_klass.base_class.sti_name)
+          klass_scope.where!(type => foreign_klass.base_class.name)
         end
 
         scope_chain_items.inject(klass_scope, &:merge!)

activerecord/test/cases/associations/eager_load_includes_full_sti_class_test.rb

@@ -11,21 +11,33 @@ module Namespaced
   end
 end
 
-class EagerLoadIncludeFullStiClassNamesTest < ActiveRecord::TestCase
+module PolymorphicFullStiClassNamesSharedTest
   def setup
+    @old_store_full_sti_class = ActiveRecord::Base.store_full_sti_class
+    ActiveRecord::Base.store_full_sti_class = store_full_sti_class
+
     post = Namespaced::Post.create(title: "Great stuff", body: "This is not", author_id: 1)
     @tagging = Tagging.create(taggable: post)
-    @old = ActiveRecord::Base.store_full_sti_class
   end
 
   def teardown
-    ActiveRecord::Base.store_full_sti_class = @old
+    ActiveRecord::Base.store_full_sti_class = @old_store_full_sti_class
+  end
+
+  def test_class_names
+    ActiveRecord::Base.store_full_sti_class = false
+    post = Namespaced::Post.find_by_title("Great stuff")
+    assert_equal @tagging, post.tagging
+
+    ActiveRecord::Base.store_full_sti_class = true
+    post = Namespaced::Post.find_by_title("Great stuff")
+    assert_equal @tagging, post.tagging
   end
 
   def test_class_names_with_includes
     ActiveRecord::Base.store_full_sti_class = false
     post = Namespaced::Post.includes(:tagging).find_by_title("Great stuff")
-    assert_nil post.tagging
+    assert_equal @tagging, post.tagging
 
     ActiveRecord::Base.store_full_sti_class = true
     post = Namespaced::Post.includes(:tagging).find_by_title("Great stuff")
@@ -35,10 +47,28 @@ class EagerLoadIncludeFullStiClassNamesTest < ActiveRecord::TestCase
   def test_class_names_with_eager_load
     ActiveRecord::Base.store_full_sti_class = false
     post = Namespaced::Post.eager_load(:tagging).find_by_title("Great stuff")
-    assert_nil post.tagging
+    assert_equal @tagging, post.tagging
 
     ActiveRecord::Base.store_full_sti_class = true
     post = Namespaced::Post.eager_load(:tagging).find_by_title("Great stuff")
     assert_equal @tagging, post.tagging
   end
 end
+
+class PolymorphicFullStiClassNamesTest < ActiveRecord::TestCase
+  include PolymorphicFullStiClassNamesSharedTest
+
+  private
+    def store_full_sti_class
+      true
+    end
+end
+
+class PolymorphicNonFullStiClassNamesTest < ActiveRecord::TestCase
+  include PolymorphicFullStiClassNamesSharedTest
+
+  private
+    def store_full_sti_class
+      false
+    end
+end