[storm] Update or add pattern with Storm

[Brad Allen]

On Fri, Oct 10, 2008 at 1:25 PM, Jamu Kakar <jkakar at canonical.com> wrote:

>
> To solve the original poster's issue, where one needs to determine
> if an object exists and then create or update it, I'd use something
> like:
>
> customer = store.find(Customer, Customer.last_name == u"Sparrow").one()
> if not customer:
>     customer = store.add(Customer(u"Jack", u"Sparrow"))
> else:
>     customer.first_name = u"Jack"
>     customer.last_name = u"Sparrow"
>
> You need to use a query that will only ever return 0 or 1 row when
> you use ResultSet.one.  If more than 1 row is returned a NotOneError
> will be raised.
>

I'm using this pattern but have found that Storm selects all the columns
when doing store.find, which is often unnecessary and exacts a performance
penalty.

Storm .13 release notes say it's possible now to address this problem:

- Expressions can be passed to Store.find() as well as classes. This
   makes it possible to request individual columns from a table,
   computed expressions or aggregates.

Is that the only way to get around this? It would be nice if I could perform
a database update without doing any select at all. Sometimes the id value of
the primary key is already available, and I just want to do an update
without selecting first.

In those situations, it would be nice if we could just do something like:

customer = Customer (id=123, first_name = u'Jack', last_name = u'Sparrow')

However, we can't use store.add for this object if we want it to generate an
update statement; Storm usually generates an insert statement for store.add
unless the object was already in the store as a result of store.find or
store.get.

I haven't tried messing around with directly setting obj_info['pending'];
that seems kind of kludgy...

(I'm still using an older branch of storm, closer to .12 than to .13. Still
haven't had time to upgrade and test everything with new Storm...)

-- 
ZeOmega
Open Minds' Open Solutions
3010 Gaylord Parkway, Ste. 210
Frisco TX, 75034
http://www.zeomega.com

Brad Allen
214-618-9880 (ext. 8006)
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