On Feb 27, 2013, at 3:12 PM, Ladislav Lenart <[email protected]> wrote:
> Hello.
>
> Thank you for your prompt answer. I will try to create a working example that
> demonstrates the issue. Though it will take me a couple of days, maybe weeks
> (my
> regular work followed by a vacation).
>
> I have another problem. I rephrased the SQL, because postgres's planner had
> issues with EXISTS and thought it is a great idea to perform full scans of
> several huge tables in order to return several hundreds result rows. Enter
> CTEs...
>
> Short-short intro:
> * Client is the joined table inheritance root.
> * PersonalClient and CorporateClient are its subclasses.
> * Partner is a salesman.
> * Deal is a contract signed between salesman(s) and client(s).
> * ImportedClientShare and ClientShare are M:N relationships between clients
> and
> deals.
> * ImportedPartnerShare and PartnerShare are M:N relationships between partners
> and deals.
> * We import deals from an external DB. Those are called imported. Imported
> deal
> has external_id and Imported*Share apply.
> * However, a user of our system (a partner) can create a new deal locally.
> Such
> a deal does not have an external id (yet) and local *Share apply to it.
>
> The following code should return all clients of a given partner via
> ImportedClientShare or via ClientShare:
>
> q1 = session.query(ImportedClientShare.client_id.label('client_id'))
> q1 = q1.join(ImportedPartnerShare, ImportedClientShare.deal_id ==
> ImportedPartnerShare.deal_id)
> q1 = q1.join(Deal, ImportedClientShare.deal_id == Deal.id)
> q1 = q1.filter(
> ImportedPartnerShare.partner_id == partner_id, # input argument
> Deal.external_id != None,
> )
> q2 = session.query(ClientShare.client_id.label('client_id'))
> q2 = q2.join(PartnerShare, ClientShare.deal_id == PartnerShare.deal_id)
> q2 = q2.join(Deal, ClientShare.deal_id == Deal.id)
> q2 = q2.filter(
> PartnerShare.partner_id == partner_id, # input argument
> Deal.external_id == None,
> )
> client_ids = q1.union(q2).cte('client_ids')
> q = session.query(Client).with_polymorphic([PersonalClient,
> CorporateClient])
> q = q.join(client_ids, Client.id == client_ids.c.client_id)
>
> NoSuchColumnError: "Could not locate column in row for column 'client.id'"
>
> I also tried it without with_polymorphic() and the result is the same.
>
> Do you have any idea what is going on / what am I doing wrong and how I can
> fix
> this?
Again, this is a very complex query, even more complex than the previous one,
and it boils down to limits in what the ORM can currently handle. It's
probably a bug, though there may be workarounds that allow it to work, however
it's the kind of issue that typically takes me many hours to diagnose and fix
or at least work around, given code that I can run and pdb in order to debug.
This is not something you'd have much luck resolving on your own unless you
wanted to become deeply familiar with SQLAlchemy internals.
I would recommend again making sure all these issues remain in the latest 0.8
version and attempting to produce a rudimentary series of test classes which I
can run in order to reproduce your results. I can reconstitute these models
looking just at your queries, though sometimes after all that effort the issue
isn't reproduced, due to some quirk in the mappings that's also required.
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