Hi !
Thanks for the prompt, and very helpful answer
I do now understand the logic a bit better
I've been able to get somewhere, so here's a status in case this is
helpful
in my own example, Record is the ancestor/common class (x in your
msg), and User is the specialization (y)
--- attempt #1
the code below kind of works - [[I've naively tried to do the copy in
some generic way, feel free to comment that part]]
# locate the object to be promoted to specialized class
rec=session.query(Record).filter_by(hrn=hrn2).first()
user=User(None,None)
# copying the ancestor fields except primary_key and disciminator
mapper=object_mapper(rec)
for column in mapper.columns:
cname=column.name
if cname == mapper.polymorphic_on.name: continue
if column.primary_key: continue
setattr(user,cname,getattr(rec,cname))
# add new instance, trash previous one
# set a user-specific column
user.email="u...@gmail.com"
session.add(user)
session.delete(rec)
session.commit()
however the side effect is that the new object - of course - has a
different primary key, which in my case can work at this early stage,
but I'm concerned about any possible relationship that would have a
hard time with that
--- attempt #2
and if now I comment out this line here, I'm getting a runtime error
# if column.primary_key: continue
in order to try and reuse the same primary_key
Traceback (most recent call last):
...
File "tuto.py", line 79, in add2 <---- this is the commit line
mentioned above
session.commit()
...
File "/usr/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py",
line 1867, in _save_obj
(table.description, len(update), rows))
sqlalchemy.orm.exc.StaleDataError: UPDATE statement on table
'tuto_users' expected to update 1 row(s); 0 were matched.
--- attempt #3
eventually I got this to do what I wanted by doing; just had to trash
& commit the deprecated instance, before I could add and commit the
new one
# locate the object to be promoted to specialized class
rec=session.query(Record).filter_by(hrn=hrn2).first()
user=User(None,None)
# copying the ancestor fields except primary_key and disciminator
mapper=object_mapper(rec)
for column in mapper.columns:
cname=column.name
if cname == mapper.polymorphic_on.name: continue
# if column.primary_key: continue
setattr(user,cname,getattr(rec,cname))
# trash previous one
session.delete(rec)
session.commit()
# set a user-specific column
user.email="u...@gmail.com"
# add new one
session.add(user)
session.commit()
--- and for the record
# rpm -q python python-sqlalchemy postgresql
python-2.7-8.fc14.1.i686
python-sqlalchemy-0.6.8-1.fc14.i686
postgresql-8.4.9-1.fc14.i686
-- Thanks again -- Thierry
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