Michael Bayer wrote:
> On Dec 22, 2009, at 2:51 PM, Igor Katson wrote:
>
>
>> I am concerned about the problem of the orm framework using SELECT's a
>> lot, which can be not used in many cases, when dealing with Postgres
>> after INSERTs or UPDATEs.
>>
>> When using postgresql, I want sqlalchemy, when updating the instance
>> parameters not to issue additional SELECTS after Session.flush() or
>> Session.commit(), but to be able to use INSERT/UPDATE...RETURNING, which
>> will update the values based on the database data.
>>
>> As far as I see, there is no such functionality in the mapper or
>> Session, and I want to extend it for personal use.
>>
>> Could you please guide me in the right direction, how to make that?
>>
>
> 0.5 supports this using the "postgres_returning" argument to update() and
> insert(), but the ORM doesn't make use of it. in 0.6, the feature has been
> generalized using the returning() method on insert() and update(), and the
> ORM will use it to fetch new primary key identifiers.
>
> It does not take effect within the ORM for inline SQL other than primary key
> identifiers, but you can use an insert() with returning() manually to achieve
> that effect.
>
Why not, Michael? Is it hard to implement this? This seems to be pretty
useful and performance-improving, reducing the amount of selects needed
when coding unaware of object expiry.
P.S. And in SQLAlchemy 0.5, what's the most orm-like way to do solve
this? In my code, it looks like this now, cause I didn't find an easier
(less lines + less sql-like code) way to do it.
columns = ','.join([str(col) for col in obj_table.c])
query = '''UPDATE %(table)s
SET col = col + %(value)s
WHERE id = %(id)s
RETURNING %(columns)s''' % {
'id': id,
'columns': columns,
'table': obj_table,
'value': value
}
obj = meta.Session.query(Obj).from_statement(query).first()
Thanks,
Igor Katson
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