[Zope3-Users] Re: Creating utilities overhead

[Philipp von Weitershausen]

Andreas Jung wrote:
> I have an utility registered as
> 
> <utility
>  provides="textindexng.interfaces.ILexicon"
>  factory="textindexng.lexicon.LexiconFactory"
>  name="txng.lexicons.default"
> 
> />
> 
> trying to create a new Lexicon instance through
> 
> lexicon zapi.createObject(None, 'txng.lexicons.default')
> 
> does not work (Zope 2.8, Five) because the factory does not seem
> to be registered for IFactory.
> 
> Adding
> 
> <utility
>  provides="zope.component.interfaces.IFactory"
>  component="textindexng.lexicon.LexionFactory"
>  name="txng.lexicons.default"
> />
> 
> resolves the issue. But why is the explicit declaration of the factory
> necessary? IMO the first declaration implies the second one. So this
> looks like configuration overhead to me...thoughts?

This is actually a mixup of the term 'factory'. The 'factory' parameter 
of the <utility /> directive might suggest that an IFactory is 
registered, but as you found out, it isn't meant that way. With the 
<utility /> directive, the parameter 'factory' means a globally 
accessible callable (class constructor, function, etc.) that creates an 
instance of the utility. Think of it as a "class factory", not a 
"factory component" in the Zope 3 sense.

If you want an IFactory utility to be registered (so you can call 
createObject, for example), you need to do this explicitly. Either with 
a separate <utility /> directive like you quoted above, or (if you want 
to save a line) with the <factory /> directive.

Philipp