Hi all,
The way single table inheritance works seem a bit "unclean" to me: all
columns are available as properties in all classes. Even if they map
to the same table, ideally each object should only have a subset of
columns available, right? SQLAlchemy can't guess which object has
which columns, so I naturally tried to map each class to a select
including only their respective columns. But I couldn't get that to
work. So I tried without inheritance and couldn't get it to work
either (see attached file).
First, it complained there was no alias, while I *think* aliases
should only be necessary when the query is used in a subquery, but
anyway, after giving it its alias, it still doesn't work: I can't save
any data. Worse, it doesn't complain in any way, it's just that no
insert is issued to the database. I suspect a limitation in SQLAlchemy
(ie no inserts when there isn't at least one complete table in the
selectable or something of the like), but it might be something I'm
doing wrong. Any idea?
BTW: it's probably related to the fact the generated select query is:
SELECT subset.id AS subset_id, subset.data AS subset_data
FROM (SELECT common.id AS id, common.data AS data FROM common) AS
subset ORDER BY subset.oid
while I'd like to be able to do is simply:
SELECT common.id AS common_id, common.data AS common_data
FROM common
ORDER BY subset.oid
--
Gaëtan de Menten
http://openhex.org
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from sqlalchemy import *
from sqlalchemy.orm import *
metadata = MetaData('sqlite:///')
metadata.bind.echo = True
common_table = Table('common', metadata,
Column('id', Integer, primary_key=True),
Column('data', Integer),
Column('extra', String(45)),
)
class Subset(object):
pass
subset_select = select([common_table.c.id, common_table.c.data]).alias('subset')
subset_mapper = mapper(Subset, subset_select)
metadata.create_all()
#common_table.insert().execute(subset_no=1)
#subset_select.insert().execute(subset_no=1)
#print [dict(e) for e in subset_select.execute().fetchall()]
sess = create_session()
l = Subset()
l.data = 1
sess.save(l)
sess.flush()
sess.clear()
print sess.query(Subset).list()
