[Zope3-Users] are aliases for content objects possible?

[Duncan McGreggor]

Hey all, these never got to the list, but the solution at the bottom 
might be of interest to others...

On Oct 3, 2005, at 10:19 PM, Duncan M. McGreggor wrote:

>>> I would like the alias to occur further back in the object hierarchy:
>>>
>>> http:/host/real_folder/object_name_1
>>> http:/host/non_existant_folder/object_name_1
>>>
>>> So, to summarize:
>>> 1) is this type of traversal modification possible in z3?, and
>>> 2) how would one go about doing this?
>>
>> I've continued to dig on this one, and the only thing I can come up 
>> with is a brute-force attempt. My thoughts are these:
>>
>> 1) If I can override the publisher 
>> (zope.app.publication.zopepublication?),
>> 2) I could use request.getTraversalStack() and do manual checks on 
>> the path, and
>> 3) For anything meeting my requirements, I do additional processing
>> 4) For everything else, pass it back to 
>> zope.app.publication.zopepublication
>>
>> Is this sane?
>>
>> If so, how would I go about "overriding the publisher"?
>>
>> If this is not sane, what is?
>
> Okay, I keep self-replying... sorry! I'm reading more code and trying 
> to think these things through...
>
> In zope.app.publication.publicationtraverse, the PublicationTraverse 
> method traverseName() does the following check:
>
>     if IPublishTraverse.providedBy(ob):
>         ob2 = ob.publishTraverse(request, nm)
>
> This happens before the check that does this:
>
>     raise NotFound(ob, name, request)
>
> The NotFound has been my biggest concern, since I don't think I can 
> use the standard Traversal behavior-changing tricks. Meaning a 
> suitable container for the content would never be arrived at, and so 
> I'd get a NotFound error. However, if I can do something with the 
> check I mentioned above, it'd be before the NotFound was generated... 
> so if whatever the "ob" object is implements IPublishTraverse, I 
> should be home-free, right? Meaning I should be able to do all the 
> "virtual directory" processing in ob.publishTraverse(). The trick is, 
> if it's not actually getting to an object nor a real container, what 
> *is* ob? Hmm... this is eerily familiar ;-) Sounds like a chapter in 
> the z3 book ;-)
>
> From zope.app.traversing.interfaces.ITraversalAPI's docstring:
>
>   Traverse a single step 'name' relative to the given object.
>
>   'name' must be a string. '.' and '..' are treated specially, as well 
> as
>   names starting with '@' or '+'. Otherwise 'name' will be treated as a
>   single path segment.
>
>   You can explicitly pass in an ITraversable as the
>   'traversable' argument. If you do not, the given object will
>   be adapted to ITraversable.
>
>   'request' is passed in when traversing from presentation code. This
>   allows paths like @@foo to work.
>
>   Raises TraversalError if path cannot be found and 'default' was
>   not provided.
>
> This is interesting. Beyond that -- this is most excellent 
> documentation. It clarifies some misconceptions I've had about 
> traversal. From this, I gather that I *should* be able to use the 
> tricks that are published in Stephan Richter's book and in the 
> schooltool code. I just have to do it further towards the root of the 
> object hierarchy. It seems that I will have to create a "site" 
> container (implementing IFolder), since it is that point in the 
> traversal process (at the level of the site) that I need to override 
> publishTraverse().
>
> This has been really, really long winded... I wanted to expose as much 
> of my thought process as possible to both get the best assistance as 
> well as provide something for future readers.
>
> For the experts out there, is my assessment correct?

To answer myself: yes, it is correct. I took a break, watched a movie, 
came back and wrote the code that only varied from Stephan's book 
example in the most minimal ways. I then restarted zope, added a new 
Site (which implements my ISite, that the custom traverser operates 
on), dumped all the content and the ++etc++site/default into the new 
one with the custom traverser, and bingo! it worked. Not even a 
hiccough.

Here's an example of the real location of an object in the site:

   http://localvhost1.com/instock/CAS1999580L

And now, with the traverser, all of the following resolve and present 
the same object as above:

   http://localvhost1.com/backhoes/CAS1999580L
   http://localvhost1.com/Backhoes/CAS1999580L
   http://localvhost1.com/BackHoes/CAS1999580L
   http://localvhost1.com/BackHoeS/CAS1999580L
   http://localvhost1.com/BACKHOES/CAS1999580L

I am frothing-at-the-mouth deliriously happy with z3. And its 
designers. Not so much about this little victory (though it is sweet), 
but rather because of the source of this little victory: the design and 
beauty of z3 itself.

At the PyCon2004 sprints, I worked with Chris McDonough and others on 
replacing the Zope 2 web server with a twisted version. For part of 
that, I spent some time hurting my eyeballs and brains trying to grok 
the Zope 2 request lifecycle and the publisher source code. It really, 
really hurt and I didn't understand much. I have resisted looking at 
z3's deep internals in part due to that past pain and the fear that I 
would meet similar dragons of my own ignorance. Not so. The component 
architecture of z3 is so simple, consistent (as far as I can tell), 
pervasive, and (honestly) fundamentally beautiful, that with a 
well-expressed docstring, understanding is almost effortless. I will be 
reading the internals of z3 from now on, with no fear :-)

Jim, Stephan, and the rest of the community: you guys have done an 
amazing, unbelievable job. Thank you for this gift to the software 
world :-) It's really changing the way I think about development, my 
development process, and ultimately, the quality and functionality of 
what I develop.

d