[Zope-dev] persistence and lists

[Casey Duncan]

Sounds like you are trying to persist a class attribute value. This is no=
t=20
possible because instance are persistent, not classes. This is also the=20
reason that the values change over all the instances. You are changing a=20
mutable attribute of the class in place.

I would suggest setting the value in the constructor of your objects, to =
make=20
sure it is an instance attribute rather than a class attr.

This:

class foo:
   def __init__(self):
       self.alist =3D []

   def append(self ,v)
       self.alist.append(v) # changes instance attr
       self._p_changed =3D 1 # will work

Instead of:

class foo:
    alist =3D []

    def append(self ,v)
        self.alist.append(v) # changes class(!) attr
        self._p_changed =3D 1 # Will not work, the instance was not chang=
ed!

hth,

Casey

On Wednesday 18 September 2002 03:27 pm, Arndt Droullier wrote:
> Hello,
> I=B4m working on a product which contains custom data in a list of mult=
iple
> dictionaries.
> How can I save the list/dictionaries after changes? Persistence is enab=
led
> (and works for other types), and "_p_changed" is set, also
> get_transaction().commit() is called.
>=20
> A second problem is that multiple instances of the product reference th=
e
> same list. So if I change the list of one of the instances the other
> changes,
> too.
> The list and dictionaries are stored in a class variable(in the product=
)
> and not global.
>=20
> Thanks, Arndt.
>=20
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