[openstack-dev] [nova] Consistency, efficiency, and safety of NovaObject.save()

Nikola Đipanov ndipanov at redhat.com
Thu Nov 13 08:52:02 UTC 2014

On 11/13/2014 02:45 AM, Dan Smith wrote:
>> I’m not sure if I’m seeing the second SELECT here either but I’m less
>> familiar with what I’m looking at.     compute_node_update() does the
>> one SELECT as we said, then it doesn’t look like
>> self._from_db_object() would emit any further SQL specific to that
>> row.
> I don't think you're missing anything. I don't see anything in that
> object code, or the other db/sqlalchemy/api.py code that looks like a
> second select. Perhaps he was referring to two *queries*, being the
> initial select and the following update?

FWIW - I think an example Matt was giving me yesterday was block devices
where we have:

def block_device_mapping_update(context, bdm_id, values, legacy=True):
    _scrub_empty_str_values(values, ['volume_size'])
    values = _from_legacy_values(values, legacy, allow_updates=True)
    query =_block_device_mapping_get_query(context).filter_by(id=bdm_id)
    return query.first()

which gets called from object save()


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