@staticmethod
def _internal_aft_hash(aft):
    """A has function representing two 'internal'.

        :class:`pydent.models.AllowableFieldType` models (i.e. an operation)
        """
    return '{operation_type}'.format(operation_type=aft.field_type.
        parent_id, routing=aft.field_type.routing, sample_type=aft.
        sample_type_id)
