Hello all,
I've been playing a bit with polymorphic concrete inheritance, and
noticed that when you have several levels of "polymorphic" loading (ie
my child class is also a parent class which I want to load
polymorphically), the query for the top-level class includes the child
polymorphic join while I don't see any reason to (its table is already
contained in the parent join). See attached example.
class A(object):
...
class B(A):
pass
class C(B):
pass
The query ends up something like:
SELECT [all_columns] FROM ([pjoin_abc]), ([pjoin_bc])
Am I using it wrong, or is this a bug?
--
Gaëtan de Menten
http://openhex.org
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from sqlalchemy import *
from sqlalchemy.orm import *
metadata = MetaData()
metadata.bind = 'sqlite:///'
a_table = Table('a', metadata,
Column('id', Integer, primary_key=True),
Column('data1', String(20))
)
b_table = Table('b', metadata,
Column('id', Integer, primary_key=True),
Column('data1', String(20)),
Column('data2', String(20))
)
c_table = Table('c', metadata,
Column('id', Integer, primary_key=True),
Column('data1', String(20)),
Column('data2', String(20)),
Column('data3', String(20))
)
metadata.create_all()
class A(object):
def __init__(self, **kwargs):
for k, v in kwargs.iteritems():
setattr(self, k, v)
class B(A):
pass
class C(B):
pass
pjoin_all = polymorphic_union({
'a': a_table,
'b': b_table,
'c': c_table
}, 'type', 'pjoin')
pjoin_bc = polymorphic_union({
'b': b_table,
'c': c_table
}, 'type', 'pjoin_bc')
a_m = mapper(A, a_table,
with_polymorphic=('*', pjoin_all),
polymorphic_on=pjoin_all.c.type,
polymorphic_identity='a')
b_m = mapper(B, b_table,
inherits=a_m, concrete=True,
with_polymorphic=('*', pjoin_bc),
polymorphic_on=pjoin_bc.c.type,
polymorphic_identity='b')
c_m = mapper(C, c_table,
inherits=b_m, concrete=True,
polymorphic_identity='c')
Session = sessionmaker()
session = Session()
a1 = A(data1='a1')
b1 = B(data1='b1', data2='b1')
c1 = C(data1='c1', data2='c1', data3='c1')
session.add(a1)
session.add(b1)
session.add(c1)
session.commit()
metadata.bind.echo = True
session.query(A).all()
print "*" * 20, "B", "*" * 20
session.query(B).all()
