Return this partition information as a PartitionId.

def identity(self):
        """Return this partition information as a PartitionId."""

        if self.dataset is None:
            # The relationship will be null until the object is committed
            s = object_session(self)

            ds = s.query(Dataset).filter(Dataset.id_ == self.d_id).one()
        else:
            ds = self.dataset

        d = {
            'id': self.id,
            'vid': self.vid,
            'name': self.name,
            'vname': self.vname,
            'ref': self.ref,
            'space': self.space,
            'time': self.time,
            'table': self.table_name,
            'grain': self.grain,
            'variant': self.variant,
            'segment': self.segment,
            'format': self.format if self.format else 'db'
        }

        return PartitionIdentity.from_dict(dict(list(ds.dict.items()) + list(d.items())))