[openstack-dev] [Glance] Replacing Glance DB code to Oslo DB code.

Robert Collins robertc at robertcollins.net
Mon Aug 19 03:07:48 UTC 2013

On 19 August 2013 14:22, Jay Pipes <jaypipes at gmail.com> wrote:

>> I'm completely with Joshua here - the ORM layer is more often than not
>> a source of bugs and performance issues.
> If used improperly, yep.


There is no proper use of an ORM.

>> We don't use the SQLAlchemy ORM for cross-SQL-DB support - thats a
>> lower layer. It's the model objects themselves that we use the ORM
>> for, and we could use SQLAlchemy's lower layers but not the ORM.
> Hmmm, not quite... see below.

>> An alternative I think would be better would be to scrap the use of
>> the SQLAlchemy ORM; keep using the DB engine abstraction support.
> Just keep in mind that the Session and Query objects and their related APIs
> are in the SQLAlchemy ORM, not the SQLAlchemy Core.

Ok, so either it's not a bright line, or we'd need to have an
alternative thing - not just a reimplementation either, cause that's

> But sure, ok.
> But then I guarantee somebody is gonna spend a bunch of time writing an
> object-oriented API to the model objects because the ORM is very useful for
> the data modification part of the DB interaction.

!cite - seriously...

> Because people will complain about having to do this:
> conn = engine.connection()
> # instances is the sqlalchemy Table object for instances
> inst_ins = instances.insert().values(blah=blah)
> ip_ins = fixed_ips.insert().values(blah=blah)
> conn.execute(ip_ins)
> conn.execute(inst_ins)
> conn.close()

This strawman is one way that it might be written. Given that a
growing set of our projects have non-SQL backends, this doesn't look
like the obvious way to phrase it to me.

> instead of this:
> i = Instance(blah=blah)
> ip = FixedIp(blah=blah)
> i.fixed_ips.append(ip)
> session.add(u)
> session.commit()
> And so you've thrown the baby out with the bathwater and made more work for
> everyone.

Perhaps; or perhaps we've avoided a raft of death-by-thousand-cuts
bugs across the project.


Robert Collins <rbtcollins at hp.com>
Distinguished Technologist
HP Converged Cloud

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