Hi all
I'm quite new to sqlalchemy and I'm very impressed by how much
experience this work is showing in its implementation.
But I've been brooding over a seemingly simple problem whose solution is
always just a step away...
Having a legacy db with simplified relations
aaa = Table( 'AAA',
metadata,
Column('pk1', String(2), primary_key=True),
Column('pk2', String(4), primary_key=True),
Column('pk3', Integer, primary_key=True))
bbb = Table( 'BBB',
metadata,
Column('pk1', String(2), primary_key=True),
Column('pk2', String(4), primary_key=True),
Column('pk3', Integer, primary_key=True))
No problem to define a one to many relation from AAA > BBB so far.
Now, as it always goes with 'legacy', some clever guy added another
table, again with a one to many relation from AAA > CCC with a catch:
ccc = Table( 'CCC',
metadata,
Column('pk4', String(6), primary_key=True),
Column('pk3', Integer, primary_key=True))
where pk4 is the concatenation of pk1 and pk2.
I tried to use column_property:
mapper(AAA, aaa,
order_by = None,
properties = {
'pk4' : column_property((aaa.c.pk1 + ord.c.pk2).label('pk4')),
'bbbs': relation(),
'cccs': relation()})
But every mentioning of pk4 throws an attribute error.
I tried to use composite:
class PK4(object):
def __init__(self, pk1, pk2):
self.pk1= pk1
self.pk2= pk2
def __composite_values__(self):
return [self.pk1, self.pk2]
def __eq__(self, other):
return other.pk1 == self.pk1 and other.pk2 == self.pk2
def __ne__(self, other):
return not self.__eq__(other)
I tried to use column_property:
mapper(AAA, aaa,
order_by = None,
properties = {
'pk4' : composite(PK4, aaa.c.pk1, aaa.c.pk2),
'bbbs': relation(),
'cccs': relation()})
Attribute errors as well in relation, but now the columns pk1 and pk2
being in the composite vanish from aaa. Maybe I'm just blind, but I'm
also grateful for a shove in the right direction.
Thank you, Werner Thie
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