Glad I could help, but I don't understand what is going on. Neither ticket
description nor the patch itself helped me. Sorry.
What is select_from() good for when it generates a cartesian query?
What MIGHT help ME (a lot infact) is a couple of DOs and DONTs examples in one
place for all these three constructs
OR
A 'highlevel user-friendly step-by-step description' about what each construct
does, so that I can see where they differ.
Anyway, keep the excellent work!
Ladislav Lenart
On 31.5.2013 01:12, Michael Bayer wrote:
> this is very helpful because you are here running into an older feature that
> I think is not very applicable to modern usage, not to mention not
> terrifically documented, so I've added
> http://www.sqlalchemy.org/trac/attachment/ticket/2736/ to address changing
> the role of select_from() to be more what it says, and to offload a
> particular magic aspect of it into a new method called select_entity_from().
>
>
> if you look at the docstrings added to the patch there, you may get a sense
> for what's been going on. I'll probably commit this soon and those docs
> will be up on the site. There will be an upgrade path for users in this case.
>
>
>
>
> On May 30, 2013, at 1:10 PM, Ladislav Lenart <[email protected]> wrote:
>
>> Hello.
>>
>> Sorry for the long delay. I finally had enough time to produce a minimal
>> self-contained regression. The attached file produces the following SQL:
>>
>> WITH RECURSIVE
>> q_cte(partner_id, max_depth) AS (
>> SELECT
>> partner.id AS partner_id,
>> 1 AS max_depth
>> FROM partner
>> WHERE partner.sponsor_id IS NULL
>> UNION ALL
>> SELECT
>> partner_alias.id AS partner_id,
>> max_depth + 1 AS max_depth
>> FROM
>> partner AS partner_alias,
>> q_cte AS q_cte_alias
>> WHERE partner_alias.sponsor_id = q_cte_alias.partner_id
>> )
>> SELECT
>> q_cte.partner_id AS q_cte_partner_id, -- suspicious
>> partner.sponsor_id AS partner_sponsor_id
>> FROM
>> q_cte
>> JOIN partner ON q_cte.partner_id = q_cte.partner_id -- BUG
>>
>>
>> I would expect this (q_cte part is correct):
>>
>> WITH RECURSIVE
>> q_cte(partner_id, max_depth) AS (
>> ...
>> )
>> SELECT
>> partner.id AS partner_id,
>> partner.sponsor_id AS partner_sponsor_id
>> FROM
>> q_cte
>> JOIN partner ON q_cte.partner_id = partner.id
>>
>>
>> The bug is somehow related to the use of select_from().
>>
>>
>> Hope this helps,
>>
>> Ladislav Lenart
>>
>>
>> On 10.5.2013 22:04, Michael Bayer wrote:
>>>
>>> On May 10, 2013, at 3:03 PM, Ladislav Lenart <[email protected]> wrote:
>>>
>>>> Hello.
>>>>
>>>> My main concern was that the query creates a cartesian product and I
>>>> thought the
>>>> warning might have something to do with it. It haven't. The problem is
>>>> related
>>>> to the use of select_from():
>>>>
>>>> q = session.query(cls, PersonalContact).select_from(q_cte_union)
>>>> q = q.join(cls, cls.id == q_cte_union.c.partner_id)
>>>>
>>>> This part renders the following SQL:
>>>>
>>>> SELECT *
>>>> FROM
>>>> q_cte
>>>> JOIN partner ON q_cte.partner_id = q_cte.partner_id
>>>>
>>>> As you can see, the JOIN condition is wrong though I have no idea why. The
>>>> following works, however:
>>>>
>>>> q = session.query(cls)
>>>> q = q.add_entity(PersonalContact)
>>>> q = q.join(q_cte_union, cls.id == q_cte_union.c.partner_id)
>>>>
>>>> Is my usage of select_from() bad for some reason? Do you know what's going
>>>> on? I
>>>> can provide you a fully runnable test case if you still need it (on
>>>> Monday).
>>>> Note also that I use SA 0.7.9. Is this fixed in later versions?
>>>
>>> I've no idea why you're getting it without more context - if everything is
>>> generated from a query(), typically the "labels" are already applied, with
>>> the exception of some operations such as subquery() (maybe cte? not sure,
>>> I'd need to try it, hence an already existing example saves me lots of time
>>> tinkering around trying to guess what you're doing).
>>>
>>> Things have been improved in 0.8 regarding same-named columns but that only
>>> applies when the labels are already present.
>>
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>>
>> <select_from_bug.py>
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