[Zope-dev] Bugtracker for z3c.relationfield and reasons for objects loosing their parent pointers

[Patrick Gerken]

On Tue, Mar 27, 2012 at 16:35, Hanno Schlichting <hanno at hannosch.eu> wrote:
> On Tue, Mar 27, 2012 at 3:50 PM, Patrick Gerken <do3ccqrv at googlemail.com> wrote:
>> Hmm, since I didn't understand what magic happens with __parent__ pointers,
>> I tried the following in pdb:
>> unwrapped = aq_base(a)
>> unwrapped.__parent__ = aq_base(a.__parent__)
>>
>> So I stored a not acquisition wrapped object onto the __parent__ attr
>> of another unwrapped object.
>> But then the result, unwrapped.__parent__ was acquisition wrapped again!
>
> Yep. That's one thing we changed in Acquisition and ExtensionClass
> 4.0a1: Prevent wrappers to be created while accessing __parent__ on
> types derived from Explicit or Implicit base classes.
>
> Usually accessing any attribute on a type derived from
> Acquisition.Explicit or Implicit will force wrapping to take place,
> unless there's already a wrapper present. Maybe you remember the whole
> weird story with browser views in Zope 2 and the need for using
> "context = aq_inner(self.context)". That was the same problem.
> Accessing the context attribute of the view (self), created a wrapper
> equivalent to: "context = context.__of__(self)", as the view itself
> wasn't wrapped in anything. For views we got rid of the problem by
> removing the Acquisition.Implicit base class.

I do remember that. Never understood why.

Thanks for the detailed explanation of all this.

Best regards,

         Patrick