[Product-Developers] Re: Local utilities - ComponentLookupError

[Martin Aspeli]

Derek Broughton wrote:
> I'm trying to implement a local utility in the manner suggested by Martin 
> Aspeli on p 275+ of /Professional Plone Development/.
> 
> The control panel stuff works fine - the entries in the configlet persist 
> over restarts of the system, and clearly the componentregistry.xml is right, 
> because (a) I can see it in portal_setup, and (b) the configlet works.
> 
> However, if I try to use the utility in Zope startup code (from 
> configure.zcml) I get a ComponentLookupError.

That's because the utility is installed in the local site registry, but 
your startup code executes outside this context and only has access to 
components in the global registry.

Think about what would happen if you have two Plone sites with different 
configuration.

> Is there some point in the startup process that I have to wait for before I 
> can use local utilities?  Or do I have to physically do something to set the 
> "Site" before I can use local utilities in startup code?

You can use zope.app.component.hooks.setSite(), but I'm not sure if 
it'll work during app startup. You'd need to get hold of the Plone site 
root somehow.

Most likely, whatever you're doing should not be done on startup. 
Perhaps you want to do it lazily on demand and cache globally? A 
variable cached with plone.memoize.forever may be an interesting option.

Martin

-- 
Author of `Professional Plone Development`, a book for developers who
want to work with Plone. See http://martinaspeli.net/plone-book