 <p>You can always use a Python property to accomplish your goal:</p> <pre><code>class ClassA(db.Model): name = db.StringProperty() def __get_classBdeleted(self): return self.classB_set.filter('deleted_flag =', 'True') classBdeleted = property(__get_classBdeleted) class ClassB(db.Model): name = db.StringProperty() deleted_flag = db.BooleanProperty() classA = db.ReferenceProperty(ClassA) </code></pre>