[Zope] Acquisition problems?

[Stephen Harrison]

Curtis Maloney wrote:
> 
[snip]
> 
> Well, here's the details:
> 
> /
>  standard_html_header
>  register
> /internal/
>         standard_html_header
> 
> register works fine if invoked as  /register
> however, it spits the dummy if invoked as /internal/register
> Complaining loudly about TypeError: too many arguments; expected 2, got 3
> in standard_html_header.

Is register a method, or a document?  If it is a method the when you
call /internal/register you are calling the object internal with the
method register, so when it looks for standard_html_header it will first
look in internal, before doing the acquisition thing.  So it finds
internal/standard_html_header.  If it is a document, then you are
calling the object /register, in the context of internal, but the
containment of / so you get /standard_html_header.

In algebra terms, if register is a method, you have

(internal o /)

but if register is a document (or folder, or other object) you have

((register o /) o (internal o /))

This is how acquisition (simple acquisition) behaves.

Of course, I am strongly of the opinion that this method of acquisition
is of very limited use and zope should really use natural acquisition
(see http://www.zope.org/Wikis/zope-dev/AcquisitionUsage for a
definition).

The problem with acquisition as it currently is is that you can't use
the example you have above to do something useful.  You can't have a
default site which you can then flavour, or skin, by adding an
overriding object high up in the context tree.

Example:

/register is the standard way of presenting the register page.

But, for internal use, you want it to look different, so you create
/internal, which replaces some of the methods (like
standard_html_header).

You should then be able to call /internal/register and see register in
the _context_ of internal, which is what is important.  The containment
of an object is only useful from an administrative point of view.  The
thing which is important is the _context_ in which the object is called.

As it is, in order to achieve the result described above you have to
carefully construct your site in order to work around the problems with
acquisition, which really isn't the way we should be doing things.

Sorry to go on about this, but as time passes I am becomming more and
more convinced that the method of acquisition needs to change from
containment before context to context before containment.

I have yet to think of any advantages provided by the current method,
but I would be more than happy to hear of any.

For reference, here a more general post on the problem I sent to the
list a while ago:

http://zope.nipltd.com/public/lists/zope-archive.nsf/ByKey/61727C8A78322A51

and here is a summary of the problem in the dev wiki:

http://www.zope.org/Wikis/zope-dev/AcquisitionFeedback

Cheers,
Stephen

-- 
Stephen Harrison            stephen@nipltd.com
New Information Paradigms   www.nipltd.com