On Jan 11, 2008 8:41 PM, Michael Bayer <[EMAIL PROTECTED]> wrote:
> what that looks like to me is that you're attempting to query the
> database for object ID #1 using merge().
>
> when you merge(), its going to treat the object similarly to how it
> does using session.save_or_update(). that is, it looks for an
> "_instance_key" attribute to determine if the object represents a
> transient or persisted instance.
>
> So you could "hack" the way youre doing it like:
>
> obj2 = ModelObject(1, u'title2')
> obj2._instance_key = session.identity_key(instance=obj2)
> session.merge(obj2)
> session.commit()
>
> we have yet to define a completely public API for the above operation,
> i.e. "treat this object as though its persistent". im not sure yet
> how we could define one that has a straightforward use case which
> wouldn't add confusion.
Sometimes this doesn't work:
--->8---
import sqlalchemy as sa, logging
from sqlalchemy.orm import mapper, sessionmaker, relation
logging.getLogger('sqlalchemy.engine').setLevel(logging.INFO)
logging.basicConfig()
class ModelObject(object):
def __init__(self, id, title):
self.id = id
self.title = title
class ModelReferer(object):
def __init__(self, id, object):
self.id = id
self.object = object
metadata = sa.MetaData()
objectsTable = sa.Table(
'Objects', metadata,
sa.Column('id', sa.Integer, primary_key=True),
sa.Column('title', sa.String(255), nullable=False),
)
referersTable = sa.Table(
'Referers', metadata,
sa.Column('id', sa.Integer, primary_key=True),
sa.Column('objectId', sa.Integer, sa.ForeignKey('Objects.id'),
nullable=False),
)
objectsMapper = mapper(ModelObject, objectsTable)
referersMapper = mapper(ModelReferer, referersTable,
properties={'object': relation(ModelObject)})
engine = sa.create_engine('sqlite://')
metadata.create_all(engine, checkfirst=True)
session = sessionmaker(bind=engine)()
def replace(session, obj):
identityKey = session.identity_key(instance=obj)
oldObj = session.get(*identityKey[:2])
if oldObj is None:
session.save(obj)
return obj
else:
obj._instance_key = identityKey
return session.merge(obj)
obj1 = ModelObject(1, u'title1')
replace(session, obj1)
ref1 = ModelReferer(1, obj1)
replace(session, ref1)
session.commit()
session.clear()
# Another program. We have to insure that object with id=1 exists in DB and has
# certain properties.
obj2 = replace(session, ModelObject(1, u'title2'))
session.commit()
ref2 = ModelReferer(1, obj2)
replace(session, ref2)
session.commit()
--->8---
The last commit fails with:
sqlalchemy.exceptions.IntegrityError: (IntegrityError)
Referers.objectId may not be NULL u'UPDATE "Referers" SET "objectId"=?
WHERE "Referers".id = ?' [None, 1]
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