[Zope-dev] zope.component.zcml and global registry

[Roger]

Hi Tres

> Betreff: Re: [Zope-dev] zope.component.zcml and global registry
> 
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Baiju M wrote:
> > On Mon, Mar 8, 2010 at 9:18 PM, Fabio Tranchitella 
> <kobold at kobold.it> wrote:
> >> * 2010-03-04 20:51, Fabio Tranchitella wrote:
> >>> Committed with tests.
> >> If nobody objects, I would like to release a new (bugfix) 
> release of 
> >> zope.component with the current trunk. This is the relevant entry 
> >> from the CHANGES.txt file:
> >>
> >> - The ZCML directives provided by zope.component now register the 
> >> components in  the registry returned by getSiteManager 
> instead of the global registry.
> >>  This allows the hooking of the getSiteManager method 
> before the load 
> >> of a  ZCML file to register the components in a custom registry.
> > 
> > Is this a feature release ?
> 
> It seems arguable either way to me:  the old behavior 
> (forcibly populating the global registry instead of the 
> hooked registry) could easily be construed as a bug.

Probably you have a very different point of view to this
changes. Let me explain what I think about that.

We have two kind of registries in zope a global/non persistent
and local/persistent in local sites. The setSite hooks forces
to set the right context for component lookup.
Note, I mean component lookup, and not component registry lookup
or register components!

ZCML based configuration actions are not persistent and can't
get registered in a local component registry. This is the 
reason why we didn't use the hooked getSiteManager method
for this configuration actions.

What this changes really does is, it allows to 
set a site which forces to use another site manager
which contains a different component registry. I don't
think setup another site is the right concept to use
another component registry. Probably there should be 
an explicit call for the IComponents utility in this case.

btw, if you like to register actions for another registry
then the global registry, there is a concept implemented in
z3c.baseregistry. It does exactly what the changes forces
to do without the possible sideeffect of register non peristent 
actions in a local persistent component registry.
With some lines of ZCML every action could register
it's handler to such another global component registry.

e.g.
<utility
  component="my.global.Registry"
  provides="zope.component.interfaces.IComponents"
  name="other"
  />
<zope:registerIn registry="my.global.Registry">
  <!-- include your ZCML here -->
</zope:registerIn>

Now, if your site provides the 'other' IComponents utility,
your fine and you will get what you need.

This concept explicit allows to register components in a
component registry and does not invoke a running application
in any way.


In my point of view, this changes/feature is implemented as simple as
possible and not done right.

If you configure a system during startup, in our case with ZCML actions,
it's really not a good idea to change the running system itself for make
this possible.

Another point, reloading ZCML actions after a system startup
e.g. from the UI is probably not possible anymore. Then we whould
have to call setSite(None) and this, on a running system, whould
force to loose the local components registry at the same time.


But anyway, if nobody objects I'm fine with this changes. I just like
to make sure everybody really knows the sideeffects of this changes
and hope we're not having problems later with this feature.

Regards
Roger Ineichen