def _validate_overriden_fields_are_not_defined_in_superclasses(class_to_field_type_overrides,
                                                               schema_graph):
    """Assert that the fields we want to override are not defined in superclasses."""
    for class_name, field_type_overrides in six.iteritems(class_to_field_type_overrides):
        for superclass_name in schema_graph.get_inheritance_set(class_name):
            if superclass_name != class_name:
                superclass = schema_graph.get_element_by_class_name(superclass_name)
                for field_name in field_type_overrides:
                    if field_name in superclass.properties:
                        raise AssertionError(
                            u'Attempting to override field "{}" from class "{}", but the field is '
                            u'defined in superclass "{}"'
                            .format(field_name, class_name, superclass_name))
Assert that the fields we want to override are not defined in superclasses.