Memoize STI class lookups for the duration of a request

activerecord/lib/active_record/base.rb

@@ -1171,7 +1171,7 @@ MSG
           if type_name.match(/^::/)
             # If the type is prefixed with a scope operator then we assume that
             # the type_name is an absolute reference.
-            type_name.constantize
+            ActiveSupport::Dependencies.constantize(type_name)
           else
             # Build a list of candidates to search for
             candidates = []
@@ -1180,7 +1180,7 @@ MSG
 
             candidates.each do |candidate|
               begin
-                constant = candidate.constantize
+                constant = ActiveSupport::Dependencies.constantize(candidate)
                 return constant if candidate == constant.to_s
               rescue NameError => e
                 # We don't want to swallow NoMethodError < NameError errors

activerecord/test/cases/base_test.rb

@@ -1409,7 +1409,7 @@ class BasicsTest < ActiveRecord::TestCase
   end
 
   def test_compute_type_no_method_error
-    String.any_instance.stubs(:constantize).raises(NoMethodError)
+    ActiveSupport::Dependencies.stubs(:constantize).raises(NoMethodError)
     assert_raises NoMethodError do
       ActiveRecord::Base.send :compute_type, 'InvalidModel'
     end