Get the deeply nested relations for a given top-level relation.

        :rtype: dict

def _nested_relations(self, relation):
        """
        Get the deeply nested relations for a given top-level relation.

        :rtype: dict
        """
        nested = {}

        for name, constraints in self._eager_load.items():
            if self._is_nested(name, relation):
                nested[name[len(relation + ".") :]] = constraints

        return nested