I'm certain sqlalchemy's got a function call in its guts that I was
about to recreate from scratch, so I'm hoping you can spare me the
trouble.
I'm trying to construct the foreign key where clause and from clause
needed to populate a relation.
I'd explain how I got here, but might take several days, so instead,
is there a function call to help me?
In other words, I've got an object, for example an order:
===================================
orderdetail_table = Table("orderdetails",metadata,
Column("orderid", Unicode, ForeignKey('orders.orderid'),
primary_key=True),
Column("lineid", Integer, primary_key=True),
Column("saleprice", Numeric, nullable=False),
Column("productid", Unicode(255),
ForeignKey('products.productid'), nullable=False)
)
product_table = Table("products", metadata,
Column("productid", Unicode(255), primary_key=True),
Column("brand", Unicode(255),
...
)
class Order(object):
pass
class OrderDetail(object):
pass
# ---------------------------- OrderDetail
-------------------------------------------------------- #
orderdetail_mapper = mapper(OrderDetail, orderdetail_table,
allow_null_pks=False,
properties=dict(product=relation(Product,
cascade='refresh-expire,expunge', #don't save
changes to Product
lazy=False)))
=====================
Say the 'product' relation is not populated on a *transient*
OrderDetail object that I will not be issuing a session flush() for
(there are errors detected.. but that's the long story).
I want to populate the transient OrderDetails 'product' attribute with
the detached product.
I assume there is no way a refresh of the 'product' attribute will
accomplish this since the parent obj is transient (which would really
be what I want), so I am also assuming I'll need to build the pk
clause and issue a session.query.get().
Since this is dynamic code (accepting any sqla object), I need to
dynamically construct that pk clause and from clause based on the
mapper's RelationProperty. In other words, use _foreign_keys to
construct this ?
But I imagine there is already a function call that will get me what I
want.
In the end, for this example, I'd want to dynamically build
session.query(Product).filter( * pk clause based on fks *)
Is there a function that can get me most everything I want (return the
pk clause) or must I build that up myself, and if myself, do you
recommend the RelationProperty's _foreign_keys attribute as the
starting point?
Thanks in advance, again.
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