Ask the collection to return a list of instances.
        If skip_exist_test is set to True, the instances returned by the
        collection won't have their primary key checked for existence.

def instances(self, skip_exist_test=False):
        """
        Ask the collection to return a list of instances.
        If skip_exist_test is set to True, the instances returned by the
        collection won't have their primary key checked for existence.
        """
        self.reset_result_type()
        self._instances = True
        self._instances_skip_exist_test = skip_exist_test
        return self