async def save(self):
        """Save this subnet."""
        if 'vlan' in self._changed_data and self._changed_data['vlan']:
            # Update uses the ID of the VLAN, not the VLAN object.
            self._changed_data['vlan'] = self._changed_data['vlan']['id']
            if (self._orig_data['vlan'] and
                    'id' in self._orig_data['vlan'] and
                    self._changed_data['vlan'] == (
                        self._orig_data['vlan']['id'])):
                # VLAN didn't really change, the object was just set to the
                # same VLAN.
                del self._changed_data['vlan']
        await super(Subnet, self).save()
Save this subnet.