Er, ok. There are simpler ways to avoid autoflush
https://bitbucket.org/zzzeek/sqlalchemy/wiki/UsageRecipes/DisableAutoflush
for example:
session = sqlalchemy.orm.object_session(mapper)
with session.no_autoflush:
target.product.quantity += (value - oldvalue)
...but that still doesn't fix your underlying problem, which is that you
are assigning an unexpected object to your "label" property. I guess
FieldStorage comes from your web framework, and you need to extract the
actual value from that before assigning it to your mapped object.
Simon
On Thu, Feb 25, 2016 at 1:24 PM, sector119 <sector...@gmail.com> wrote:
> Thanks a lot, I add
>
> @event.listens_for(ProductFlavor, 'after_update')
> def quantity_before_update_listener(mapper, connection, target):
> quantity =
> select([func.coalesce(func.sum(ProductFlavor.__table__.c.quantity),
> 0)]).where(
> ProductFlavor.__table__.c.product_id == Product.__table__.c.id)
> connection.execute(
> Product.__table__.update().where(Product.__table__.c.id ==
> target.product_id).values(quantity=quantity))
>
>
> четверг, 25 февраля 2016 г., 11:52:50 UTC+2 пользователь Simon King
> написал:
>>
>> On Wed, Feb 24, 2016 at 9:51 PM, sector119 <sect...@gmail.com> wrote:
>>
>>> Hello!
>>>
>>> I have two models, Product and ProductFlavor with one-to-many
>>> relationship
>>> And I have a listener, which I want to update Product.quantity on
>>> ProductFlavor.quantity change:
>>>
>>> @event.listens_for(ProductFlavor.quantity, 'set')
>>> def quantity_set(target, value, oldvalue, initiator):
>>> if value != oldvalue:
>>> target.product.quantity += (value - oldvalue)
>>>
>>>
>>> But I get the following error:
>>>
>>>
>>> ProgrammingError: (raised as a result of Query-invoked autoflush;
>>> consider using a session.no_autoflush block if this flush is occurring
>>> prematurely)
>>>
>>> (psycopg2.ProgrammingError) can't adapt type 'instance' [SQL: 'UPDATE
>>> product_flavor SET label=%(label)s WHERE product_flavor.id =
>>> %(product_flavor_id)s'] [parameters: {'product_flavor_id': 4, 'label':
>>> FieldStorage('label', u'42bbebd1f7ba46b58d3d4b794b4b890e.png')}]
>>>
>>> What I'm doing wrong?
>>>
>>
>> It looks like you're assigning a non-string to your "label" column. This
>> isn't directly related to your attribute listener - the error would happen
>> even without the attribute listener when you called session.flush() or
>> session.commit(). The attribute listener is just causing the flush to
>> happen earlier presumably because "target.product" has not yet been loaded
>> from the database.
>>
>> Simon
>>
>>
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