'Do not allow other than own_project_id.'

def _check_cross_project_references(self, own_project_id, visibility_field):

    def check_project_id(subfilter):
        (op, value) = list(subfilter.items())[0]
        if ((op.lower() not in self.complex_operators) and (list(value.keys())[0] == visibility_field) and (value[visibility_field] != own_project_id)):
            raise base.ProjectNotAuthorized(value[visibility_field])
    self._traverse_postorder(self.filter_expr, check_project_id)
