def get_last_tid(self):
        try:
            spec = {'tid': {'$gt': 0}}
            sort = [('tid', -1)]
            row = self.db.docs.find_one(spec, sort=sort)
        except Exception as e:
            raise DatabaseException(e)
        if row:
            return row['tid']
        return 0
def save(self, verbosity=1, *args, **kwargs):
        connection = connections[get_tenant_database_alias()]
        is_new = self.pk is None
        has_schema = hasattr(connection, 'schema_name')
        if has_schema and is_new and connection.schema_name != get_public_schema_name():
            raise Exception("Can't create tenant outside the public schema. "
                            "Current schema is %s." % connection.schema_name)
        elif has_schema and not is_new and connection.schema_name not in (self.schema_name, get_public_schema_name()):
            raise Exception("Can't update tenant outside it's own schema or "
                            "the public schema. Current schema is %s."
                            % connection.schema_name)

        super().save(*args, **kwargs)

        if has_schema and is_new and self.auto_create_schema:
            try:
                self.create_schema(check_if_exists=True, verbosity=verbosity)
                post_schema_sync.send(sender=TenantMixin, tenant=self.serializable_fields())
            except Exception:
                # We failed creating the tenant, delete what we created and
                # re-raise the exception
                self.delete(force_drop=True)
                raise
        elif is_new:
            # although we are not using the schema functions directly, the signal might be registered by a listener
            schema_needs_to_be_sync.send(sender=TenantMixin, tenant=self.serializable_fields())
        elif not is_new and self.auto_create_schema and not schema_exists(self.schema_name):
            # Create schemas for existing models, deleting only the schema on failure
            try:
                self.create_schema(check_if_exists=True, verbosity=verbosity)
                post_schema_sync.send(sender=TenantMixin, tenant=self.serializable_fields())
            except Exception:
                # We failed creating the schema, delete what we created and
                # re-raise the exception
                self._drop_schema()
                raise