Fix ActiveRecord `subclass_from_attrs` when eager_load is false.

It cannot find subclass because all classes are loaded automatically
when it needs.

1 files changed, 3 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/inheritance.rb b/activerecord/lib/active_record/inheritance.rb
index e630897a4b..e4586f74fc 100644
--- a/activerecord/lib/active_record/inheritance.rb
+++ b/activerecord/lib/active_record/inheritance.rb
@@ -167,8 +167,9 @@ module ActiveRecord
       # this will ignore the inheritance column and return nil
       def subclass_from_attrs(attrs)
         subclass_name = attrs.with_indifferent_access[inheritance_column]
-        return nil if subclass_name.blank? || subclass_name == self.name
-        unless subclass = subclasses.detect { |sub| sub.name == subclass_name }
+        return if subclass_name.blank? || subclass_name == self.name
+        subclass = subclass_name.safe_constantize
+        unless subclasses.include?(subclass)
           raise ActiveRecord::SubclassNotFound.new("Invalid single-table inheritance type: #{subclass_name} is not a subclass of #{name}")
         end
         subclass