yah I know what this is, and I should probably change it. In the
beginning, when I started playing with "attribute decorators" on classes
for this, I said, OK, we want to be as transparent as possible. So if you
create your object:
x = Foo()
then all the attributes that you havent set yet should act like regular
attributes:
x.lala -> AttributeError ! since it was never set.
But when you pull a Foo from the database, the NULL column from the result
set gets set on the object as "None". so its not totally consistent.
So maybe, since a mapper *is* explicitly defining class attributes anyway,
including adding blank lists for list attributes, the attribute decoration
system should just return None as the default instead of raising
AttributeError...this logic occurs on line 275 of sqlalchemy/attributes.py
....try changing it to return None instead of raising AttributeError. Ill
look into this further as well.
- mike
Robin Munn wrote:
> I've been playing around with SQLAlchemy at the interactive Python
> prompt, and I've discovered an interesting quirk. I can't tell if it's
> a bug or not; if it's not a bug, then perhaps someone can explain why
> it acts this way.
>
> I created a simple table structure:
>
> from sqlalchemy import *
>
> engine = create_engine('sqlite://filename=foo.db')
>
> class Person(object):
> pass
>
> person = Table('person', engine,
> Column('id', Integer, Sequence('person_id_seq'), primary_key=True),
> Column('lname', String),
> Column('fname', String),
> Column('age', Integer),
> )
> person.create()
>
> assign_mapper(Person, person)
>
>
> And then went to the Python prompt and pasted the above in. Then I
> created a couple of Person objects:
>
>>>> john = Person(fname='John', lname='Doe', age=42)
>>>> mary = Person(fname='Mary', lname='Smith') # Age not given
>>>> objectstore.commit()
>>>> john.fname
> 'John'
>>>> john.age
> 42
>>>> mary.fname
> 'Mary'
>>>> mary.age
> Traceback (most recent call last):
> File "<stdin>", line 1, in ?
> File
> "/home/rmunn/projects/python/sqlalchemy/lib/sqlalchemy/attributes.py",
> line 51, in get_prop
> return self.attribute_registry().get_attribute(obj, key)
> File
> "/home/rmunn/projects/python/sqlalchemy/lib/sqlalchemy/attributes.py",
> line 275, in get_attribute
> raise AttributeError(key)
> AttributeError: age
>
>
> I'd been expecting to get "None" for Mary's age, since it's a NULL in
> the database. If I quit the Python interpreter and come back to it,
> then things work as I expect:
>
>>>> john = Person.get(1)
>>>> mary = Person.get(2)
>>>> john.fname
> u'John'
>>>> mary.fname
> u'Mary'
>>>> john.age
> 42
>>>> mary.age
>>>> mary.age is None
> True
>
>
> But if I create a Person object without specifying its age, and then
> try to get the "age" attribute within the same Python session, it
> fails with an AttributeError exception. I tried working around this by
> doing an objectstore.commit() and fetching the object back with
> Person.get(), but that doesn't work:
>
>>>> susan = Person(fname='Susan', lname='Smith') # No age given
>>>> objectstore.commit()
>>>> susan.fname
> 'Susan'
>>>> susan.id
> 3
>>>> new_obj = Person.get(3)
>>>> new_obj is susan
> True
>>>> # Probably won't work then, but let's try it
> ...
>>>> new_obj.age
> Traceback (most recent call last):
> File "<stdin>", line 1, in ?
> File
> "/home/rmunn/projects/python/sqlalchemy/lib/sqlalchemy/attributes.py",
> line 51, in get_prop
> return self.attribute_registry().get_attribute(obj, key)
> File
> "/home/rmunn/projects/python/sqlalchemy/lib/sqlalchemy/attributes.py",
> line 275, in get_attribute
> raise AttributeError(key)
> AttributeError: age
>
>
> Is this expected behavior? How should I go about fetching the age
> value for a Person object I've just created, if I didn't specify one
> in the first place? I've been reading through the documentation; if
> there's anything that talks about this case, I haven't found it yet.
>
> Any help would be appreciated.
>
> --
> Robin Munn
> [EMAIL PROTECTED]
> GPG key 0xD6497014
>
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