[Zope3-Users] Referencing objects

[Simon Elbaz]

Hi,
here is what I have understood in zope3 security policy:

On Mon, Feb 21, 2011 at 1:28 PM, Michael Seifert <michael.seifert at gmx.net>wrote:

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> Am 04.02.2011 17:04, schrieb Thierry Florac:
> > Hi,
> >
> >
> > Le vendredi  4 février 2011,
> >   Michael Seifert <michael.seifert at gmx.net> a écrit :
> > ======================================================================
> >> Hello everyone,
> >
> >> I recently started a Zope3 project, but I am stuck at the very
> >> beginning. Although I have some experience with Zope2, the more
> >> flexible approach to developing web applications was giving me a
> >> really hard start. Let me point out my situation:
> >> I created a container hierarchy which is stored in ZODB. Say I have a
> >> set of object types A, B, C, D, whose relationships look like the
> >> following (edges represent containment, i.e. A contains B,... where B
> >> and D are in subcontainers of A):
> >
> >>     A
> >>    / \
> >>   B   D
> >>   |
> >>   C
> >
> >> C has an attribute referencing an object of type D. As this attribute
> >> is mandatory on creation, I created a vocabulary, which ascends the
> >> hierarchy from the current context until it reaches A and returns all
> >> objects of type D.
> >> Now the part that doesn't work:
> >> While ascending from C to B and from B to A works fine, descending
> >> from A to D returns a security proxied object and since these objects
> >> cannot be pickled, I cannot store it's reference in the attribute of
> >> C.
> >
> >> 1. Is this the way it's meant to be done? :) What is your opinion of
> >> storing B and D objects in subcontainers of A?
> >
> > That shouldn't be a problem, it's not different when you use a "basic"
> > folder-like container which, internally, stores sub-objects in an
> > internal b-tree container ; the only difference here is that you own
> > two internal containment attributes.
> >
> >
> >> 2. Are there any means to turn the vocabulary into trusted code, so it
> >> will not be encapsulated in a proxy (without deactivating the security
> >> proxy)?
> >
> > Perhaps can you use the "removeSecurityProxy" function ?
> >
> >
> >> 3. How do you reference objects like you do with foreign keys in
> >> relational databases? I want to do this to prevent objects from being
> >> saved multiple times.
> >
> > If the targetted object is persistent (and so a subclass of
> > "Persistent" class), it should be stored only once in the database
> > (just try to alter properties of an object and check if the other one
> > is also modified or not to check !)
> > Another way I commonly use to store references is to store only an
> > IIntIds utility reference, which is an integer ; the benefit of this
> > is that this value can easilly be indexed.
> >
> > Regards,
> > Thierry
>
> Thanks Thierry, your answer helped a lot.
>
> I solved the issue with:
> from zope.security.proxy import removeSecurityProxy
> def vocab(context):
>        ...
>        return SimpleVocabulary.fromValues([removeSecurityProxy(elem) for
> elem
> in context.values()]))
>
>
> Still, I have some questions regarding the security.
>
> 1.
> When creating the vocabulary with
> return SimpleVocabulary.fromValues([elem.someFunc() for elem in
> context.values()]))
> I noticed that elem in context.values() are not proxied yet, so the
> actual wrapping must take place before the values are passed to the ZMI.
> How does calling the removeSecurityProxy function prevent the objects
> from being wrapped, since the wrapping takes place AFTER the function call?
> (I had a look at the sources, but the implementation resides in
> zope.security._proxy which is a binary .so file)
>
>
>
The removeSecurityProxy does not prevent the object from being proxied: it
allows the storage of the object in an attribute without its proxy.
The original object will always be proxied.


> 2.
> The vocabularies are registered as utilities in the .zcml file(s).
> Since access to objects from these vocabularies is not checked by a
> security proxy: Is it therefore possible that any user can access the
> vocabulary data?
> If so, is there a way to restrict access to the utility vocabularies?
>
>
You can use the utility permission attribute.



> Regards,
> Michael
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Regards,
Simon
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