'Create nested fields for forward and reverse relationships.'

def build_nested_field(self, field_name, relation_info, nested_depth):

    class NestedSerializer(ModelSerializer, ):
        class Meta:
            model = relation_info.related_model
            depth = (nested_depth - 1)
            fields = u'__all__'
    field_class = NestedSerializer
    field_kwargs = get_nested_relation_kwargs(relation_info)
    return (field_class, field_kwargs)
