Fix #exists? for AR::Model

activerecord/lib/active_record/relation/finder_methods.rb

@@ -187,7 +187,7 @@ def all(*args)
     def exists?(id = false)
       return false if id.nil?
 
-      id = id.id if ActiveRecord::Base === id
+      id = id.id if ActiveRecord::Model === id
 
       join_dependency = construct_join_dependency_for_association_find
       relation = construct_relation_for_association_find(join_dependency)

activerecord/test/cases/inclusion_test.rb

@@ -18,6 +18,11 @@ def test_inherited_model
   def test_generated_feature_methods
     assert Teapot < Teapot::GeneratedFeatureMethods
   end
+
+  def test_exists
+    t = Teapot.create!(:name => "Ronnie Kemper")
+    assert Teapot.exists?(t)
+  end
 end
 
 class InclusionUnitTest < ActiveRecord::TestCase