> On Nov 24, 2014, at 1:00 AM, Victor Reichert <vfr...@gmail.com> wrote:
>
> I've taken another look at trying to eager load the address.parent. Is it
> possible to do that?
Unfortuntately not really. It should be in theory but I’m not able to work
out an eager load that goes to both Customer and Supplier in terms of
AddressAssociation at the same time. I can get the query to render just fine
but the eager-targeting logic at the moment doesn’t seem to know how to be told
to go to two separate subclasses of a base class at the same time. There’s
probably improvements yet to be made in eager loading to support this case
better, e.g. this is a bug, but I’ve wrestled with it for about an hour and I’m
out of time on it for now, sorry. Even if it works, the query is very
unpleasant to look at :) If I get it working later I’ll send it out.
There’s also a bug in the example, add this, it will help a lot:
diff --git a/examples/generic_associations/discriminator_on_association.py
b/examples/generic_associations/discriminator_on_association.py
index e03cfec..7bb04cf 100644
--- a/examples/generic_associations/discriminator_on_association.py
+++ b/examples/generic_associations/discriminator_on_association.py
@@ -84,6 +84,7 @@ class HasAddresses(object):
"%sAddressAssociation" % name,
(AddressAssociation, ),
dict(
+ __tablename__=None,
__mapper_args__={
"polymorphic_identity": discriminator
}
this is to override the automated __tablename__ thing in the example.
>
> I've tried a couple of ways, pasted a below. My full code is at:
> https://gist.github.com/vfr292/a5939418285e4c8bd03b
> <https://gist.github.com/vfr292/a5939418285e4c8bd03b>
the first query should be:
eager_sales_persons = session.query(SalesPerson).options(
joinedload(SalesPerson.customers).
joinedload(Customer.addresses.attr[0]).
joinedload(Customer.addresses.attr[1])
).all()
>
> eager_addresses = session.query(Address).options(joinedload(Address.parent))
>
> #error sqlalchemy.exc.ArgumentError: mapper option expects string key or list
> of attributes
>
> eager_addresses =
> session.query(Address).options(joinedload(Address.association).joinedload(Customer.assoc_cls.parent),
> joinedload(Address.association).joinedload(Supplier.assoc_cls.parent)).all()
>
> #not joining to Customer or Supplier
>
> eager_addresses =
> session.query(Address).outerjoin(Address.association).outerjoin(Customer.assoc_cls.parent).options(contains_eager(Address.parent)).outerjoin(Supplier.assoc_cls.parent).options(contains_eager(Address.parent).all())
>
> #error sqlalchemy.exc.ArgumentError: mapper option expects string key or list
> of attributes
>
> Any advice on how I can eager load address.parent would be much appreciated :)
>
> Sincere thanks,
>
> ~Victor
>
> On Sunday, October 26, 2014 3:06:13 AM UTC-7, Michael Bayer wrote:
>
>> On Oct 26, 2014, at 12:07 AM, Victor Reichert <vfr...@gmail.com
>> <javascript:>> wrote:
>>
>> Hi,
>>
>> I am following the "Generic Association with Discriminator on Association"
>> example at:
>>
>> http://docs.sqlalchemy.org/en/latest/_modules/examples/generic_associations/discriminator_on_association.html
>>
>> <http://docs.sqlalchemy.org/en/latest/_modules/examples/generic_associations/discriminator_on_association.html>
>>
>> However, I would like to eager load the customer.addresses in a query like
>>
>> eager_sales_persons =
>> session.query(SalesPerson).options(joinedload(SalesPerson.customers).joinedload(Customer.addresses))
>>
>> #with SalesPerson being a class I added with a relationship to customers.
>>
>> However, the above statement raises: 'AssociationProxy' object has no
>> attribute 'property'
>>
>> I tried eager_sales_persons =
>> session.query(SalesPerson).options(joinedload(SalesPerson.customers).joinedload(Customer.address_association).joinedload(AddressAssociation.addresses)).all()
>>
>> however, it would emit SQL for customer.addresses.
>>
>> I have made a pastie with my code at: http://pastie.org/9676017
>> <http://pastie.org/9676017>
>> Is there a loader strategy that would work for my situation or a work around
>> for the AssociationProxy error?
>>
>>
>
> the second query is the right one, as currently there isn’t integration
> between an association proxy attribute and loader options, meaning, you have
> to state the joinedload() in terms of the actual relationship() as you are
> doing.
>
> However I’m not seeing the problem:
>
> if we load as :
>
>
> session.query(SalesPerson).options(joinedload(SalesPerson.customers).joinedload(Customer.address_association).joinedload(AddressAssociation.addresses)).all()
>
> which you can also state like this:
>
>
> session.query(SalesPerson).options(joinedload(SalesPerson.customers).joinedload("address_association").joinedload(“addresses")).all()
>
> setting echo=True on create_engine(), the main query is:
>
> SELECT salesperson.id <http://salesperson.id/> AS salesperson_id,
> salesperson.name <http://salesperson.name/> AS salesperson_name,
> address_association_1.id <http://address_association_1.id/> AS
> address_association_1_id, address_association_1.discriminator AS
> address_association_1_discriminator, address_1.id <http://address_1.id/> AS
> address_1_id, address_1.association_id AS address_1_association_id,
> address_1.street AS address_1_street, address_1.city AS address_1_city,
> address_1.zip AS address_1_zip, customer_1.id <http://customer_1.id/> AS
> customer_1_id, customer_1.name <http://customer_1.name/> AS customer_1_name,
> customer_1.sales_person_id AS customer_1_sales_person_id,
> customer_1.address_association_id AS customer_1_address_association_id
> FROM salesperson LEFT OUTER JOIN customer AS customer_1 ON salesperson.id
> <http://salesperson.id/> = customer_1.sales_person_id LEFT OUTER JOIN
> address_association AS address_association_1 ON address_association_1.id
> <http://address_association_1.id/> = customer_1.address_association_id LEFT
> OUTER JOIN address AS address_1 ON address_association_1.id
> <http://address_association_1.id/> = address_1.association_id
>
>
> so in the FROM we have: salesperson -> customer -> address_association ->
> address
>
> that’s correct. you’ll note three joinedload() calls, three links (->).
>
> then as the iteration proceeds, the sample calls upon address.parent. This
> emits this query for two entries:
>
> SELECT customer.id <http://customer.id/> AS customer_id, customer.name
> <http://customer.name/> AS customer_name, customer.sales_person_id AS
> customer_sales_person_id, customer.address_association_id AS
> customer_address_association_id
> FROM customer
> WHERE ? = customer.address_association_id
>
> not sure if that’s the query you’re referring to. That’s Address.parent,
> which is a proxy to CustomerAddressAssociation.parent, which is emitting a
> lazy load. As this is the non-FK side of a one-to-one, that’s also correct.
> A one-to-one is a special case of a one-to-many, basically, uselist=False
> means, fetch a one-to-many collection, but only deal with the first result.
> CustomerAddressAssociation.parent is the backref of the
> Customer.address_association many-to-one that’s stated in the joinedload().
>
> if this were a non-generic mapping where Customer.addresses were a
> one-to-many and Address.parent were a many-to-one, you wouldn’t get that
> extra load for Address.parent; a pure many-to-one is implicitly retrieved
> from the database and cached that way when the one-to-many side is loaded.
> but in this case the “generic” mapping has flipped this around so that
> Customer->AddressAssoiation is a many-to-one.
>
>
>
>
>
>
>
>> Thank you so much for your help :)
>>
>> ~Victor
>>
>>
>> --
>> You received this message because you are subscribed to the Google Groups
>> "sqlalchemy" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to sqlalchemy+...@googlegroups.com <javascript:>.
>> To post to this group, send email to sqlal...@googlegroups.com <javascript:>.
>> Visit this group at http://groups.google.com/group/sqlalchemy
>> <http://groups.google.com/group/sqlalchemy>.
>> For more options, visit https://groups.google.com/d/optout
>> <https://groups.google.com/d/optout>.
>
>
> --
> You received this message because you are subscribed to the Google Groups
> "sqlalchemy" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to sqlalchemy+unsubscr...@googlegroups.com
> <mailto:sqlalchemy+unsubscr...@googlegroups.com>.
> To post to this group, send email to sqlalchemy@googlegroups.com
> <mailto:sqlalchemy@googlegroups.com>.
> Visit this group at http://groups.google.com/group/sqlalchemy
> <http://groups.google.com/group/sqlalchemy>.
> For more options, visit https://groups.google.com/d/optout
> <https://groups.google.com/d/optout>.
--
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to sqlalchemy+unsubscr...@googlegroups.com.
To post to this group, send email to sqlalchemy@googlegroups.com.
Visit this group at http://groups.google.com/group/sqlalchemy.
For more options, visit https://groups.google.com/d/optout.
