Don't allow to automatically query database when use load_only option

[toan nguyen]

When I query object like that:

user = session.query(User).options(load_only('id', 'email')).first()

If I use user object but I don't remember I only loaded 'email', 'id' columns and used like that:

print user.name 

It'll automatically query database to set 'name' attribute. I want an option for me to don't allow it to do automatic. Because of special reason, I can't query like that

user = session.query(User.id, User.email).first()

[Mike Bayer]

what is the "special reason"? query(User.id, User.email) would give you exactly what you want.

if the query is more composed than that, you can use a bundle:

from sqlalchemy.orm import Bundle
user = session.query(Bundle('user', User.id, User.email))

or another option, expunge it:

user = session.query(User).first()
session.expunge(user)

there's a noload() option but right now it only applies to relationship properties.

[toan nguyen]

Because I want return result of query must be an instance of model in orm

[Mike Bayer]

so expunge() it, or .close() the session that you loaded with. hows that ? otherwise it represents a proxy to a database row.

I also will be working on patterns soon to integrate "Bundle" with ORM objects as far as methods and other behaviors. bundles load much faster as they aren't identity mapped.

[toan nguyen]

I can't use expunge() or close() because I still use object in session such as set user.age = 20. Anyway, thank u so much.

[Mike Bayer]

there's no option built in but in 0.9 we have an "uninstrumented" column loader, which you can enable using the loader API at a finer grained level:

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class User(Base):
    __tablename__ = 'user'

    id = Column(Integer, primary_key=True)
    name = Column(String)
    email = Column(String)

e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)
sess = Session(e)

sess.add(User(name='n1', email='e1'))
sess.commit()

opt1 = Load(User).set_column_strategy(
                    ['id', 'email'], {'deferred': False, 'instrument': True}
                ).set_column_strategy(
                    '*', {'deferred': False, 'instrument': False}
                )

u1 = sess.query(User).options(opt1).first()
print u1.name

this won't render SQL but will return "None" for .name, it won't raise. There's even more stable API that can be used to inject a "raise on access" handler in there if that's interesting.

[toan nguyen]

Yeah, this solution is very helpful for me.

[toan nguyen]

Resolved