On Mar 31, 2008, at 11:37 PM, askel wrote:
>
> Hello everybody,
>
> I'm wondering if there is a "standard" way of doing something like the
> following:
>
> masters = Table('masters', meta,
> Column('id', Integer, primary_key=True),
> Column('name', String, unique, nullable=False)
> )
>
> details = Table('details', meta,
> Column('id', Integer, primary_key=True),
> Column('master_id', Integer, ForeignKey('masters.id'),
> nullable=False),
> Column('name', String, nullable=False),
> UniqueConstraint('master_id', 'name')
> )
>
> class Master(object): pass
>
> mapper(Master, masters, properties={'details': relation(Detail)})
>
> class Detail(object):
> def __init__(self, master_name, name):
> '''Magic happens here
> assigning to master_name forces master_id to be magically resolved
> later on, probably by MapperExtension
> '''
> self.master_name = master_name
> self.name = name
>
> mapper(Detail, details, properties={'master': relation(Master)})
>
The master_id FK attribute is populated upon flush(), when you've
associated a Master and Detail object with each other beforehand.
If you want to construct a Detail that loads its Master in, just do it
in the constructor:
class Detail(object):
def __init__(self, master_name, name):
self.master =
session.query(Detail).filter(Master.name==master_name).one()
This kind of pattern tends to work nicely when you're using a thread-
local ScopedSession so that theres no need to pass one into Detail's
constructor.
Also, the bidirectional relationship is better served by a single
backref rather than two distinct properties:
mapper(Detail, details)
mapper(Master, masters, properties={'details': relation(Detail,
backref='master')})
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