sorry, either:
results = session.query(Book).options(
orm.undefer(Book.num_purchased),
orm.contains_eager('purchases')
).order_by("calculated_books_num_purchased").\
limit(50).from_self().outerjoin(Book.purchases).all()
or
results = session.query(Book).options(
orm.undefer(Book.num_purchased),
orm.contains_eager('purchases')
).order_by(Book.num_purchased).\
limit(50).from_self().outerjoin(Book.purchases).all()
the latter is more guaranteed to work correctly though may be less efficient
depending on backend.
On Jun 8, 2011, at 12:47 AM, Michael Bayer wrote:
> you can do it manually as the combination of automatic joins and ordering by
> subqueries seems to get tripped up (its a bug, but not sure of the nature of
> it)
>
> results = session.query(Book).options(
> orm.undefer(Book.num_purchased),
> orm.contains_eager('purchases')
>
> ).limit(50).from_self().outerjoin(Book.purchases).all()
>
>
>
>
> On Jun 7, 2011, at 7:12 PM, Yoann Roman wrote:
>
>> I ran into a problem with a rather unique query on SA 0.6.5
>> (reproducible on 0.7.1). The query eagerloads a collection, undefers a
>> scalar-select column, orders on the latter, and applies a limit/
>> offset. To order by a scalar-select column without executing the
>> subquery again, I have to apply a custom label on the select and use
>> that in the order_by. The problem is that, when SA nests the query
>> because of the limit/eagerload combo, it tacks on the order_by columns
>> again, which fails since the custom label isn't valid by itself.
>>
>> Here is a self-contained script to illustrate the problem:
>> http://dl.dropbox.com/u/45702/deferred.py
>>
>> The problem, on SA 0.6.5, came down to line 2390 of
>> sqlalchemy.orm.query.Query._compile_context.
>>
>> Is this a bug or is there a better way to do the above?
>>
>> Thanks.
>>
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