[Zope] Persistent references to persistent objects ?!?!

[Jean-Francois.Doyon at CCRS.NRCan.gc.ca]

Dieter,

Once again, thanks for the good points.  Obviously one wouldn't want to
create a catalog index on an attribute that just stored references ...
that'd be kind of silly, and I'm sure I'd know better :) Security is pretty
obviously a concern.  As for acquisition, I guess the traversal would happen
from the actual object's (Being referenced) point in the tree, not the
reference ? (Not that I'd rely on that, I'm just curious at this point).

As for Zope 3, yeah well I keep on eye on the development there, but I'm
pretty much planning for the worst and a complete review of my code for it
anyways, taking full advantage of the new design philosophies in it. (Just
planning for the worst mind you).

Acquisition has great benefits I must admit.  What's always left me ...
second-guessing ? the concept, is the acquisition of attributes ... THAT can
be quite offputting sometimes.  Acquiring objects along the tree however is
great, and simplifies incredibly the effort of reducing dupplication of
logic or content.
In fact, removal of acquisition alone will mean reviewing our site(s)
because we depend on it to share content (Move shared content up the tree to
the closest common denominator).

All in all I'm pretty sure those that use it would like to keep it (At least
in some form).  I'd suggest since someone from Zope corp is reading, that
this should be a feature that stays, but with manager control.  The
administrator could turn on or off global acquisition, select what gets
acquired (instances vs attributes) and how, and so on ... Besides I vaguely
recall reading that there will be *some* acquisition available, but much
more restricted in nature ?
I have to guess someone will eventualy add a context wrapper that DOES do it
anyway, even as a third party ?

Thanks,
J.F.

-----Original Message-----
From: Dieter Maurer [mailto:dieter at handshake.de]
Sent: Saturday, February 07, 2004 7:42 AM
To: Jean-Francois.Doyon at CCRS.NRCan.gc.ca
Cc: zope at zope.org
Subject: RE: [Zope] Persistent references to persistent objects ?!?!


Jean-Francois.Doyon at CCRS.NRCan.gc.ca wrote at 2004-2-6 16:55 -0500:
>Hmmm interesting point.  I suppose a basic rule of thumb would be that the
>reference should never be stored directly as an attribute of a folderish
>type ?
>
>I can imagine many useful scenarios where keeping references to objects can
>be very handy (Versioning, workflow, lists of objects, etc ...) ...
Although
>I have to admit the symlink think had never really even occured to me.  I'd
>imagine instead maintaining a list of references for instance, maybe stored
>as an attribute of some other non-folderish type ... you know maybe build
>some content-type class that, as part of it's functionality, keeps
>references to objects ?  This should make it safe from any unexpected
>behavior like the one you describe, right ?

I do not think so.

  You must be prepared that objects retrieved via persistent
  references maintained by yourself behave differently than
  those maintained by the "standard" references.

  Watch out for any situation where the acquisition context
  is relevant: e.g. indexing, security, locating of central
  resources (like "MailHost"), ...

Taking enough care, you will probably be able to cope with the
situation.

Your type of usage may be affected by Zope 3.

  Zope 3 has abandonned acquisition (called "context wrapper"s
  in Zope 3 terms) (personally, I am sad about this; "acquisition"
  has been one of my major selling points for Zope).

  In Zope 3, objects contain a reference to their parent in
  the hierarchy.
  This means that objects know their place in the hierarchy
  which may make it easier to have references to them
  in various places.

-- 
Dieter