Returns a list of instances for each given pk, respecting the condition
        about checking or not if a pk exists.

def _to_instances(self, pks):
        """
        Returns a list of instances for each given pk, respecting the condition
        about checking or not if a pk exists.
        """
        # we want instances, so create an object for each pk, without
        # checking for pk existence if asked
        meth = self.cls.lazy_connect if self._instances_skip_exist_test else self.cls
        return [meth(pk) for pk in pks]