[Grok-dev] Time for a global_adapter?

Martin Aspeli optilude+lists at gmail.com
Thu Apr 9 05:00:43 EDT 2009

Martijn Faassen wrote:
> Hey,
> Martin Aspeli wrote:
>> If I'm not missing something, it's not possible to do this without ZCML:
>>    from z3c.form.widget import ComputedWidgetAttribute(
>>    def getDefault(data):
>>        return "blah"
>>    DefaultValueProvider = ComputedWidgetAttribute(
>> 		getDefault,  field=IMySchema['some_field'])
>>    <adapter factory=".DefaultValueProvider" name="default" />
>> That is - I'm using a factory (ComputedWidgetAttribute in this case) to 
>> obtain an adapter, which I then need to register under a name.
>> I could imagine something like:
>>    grok.global_adapter(DefaultValueProvider, name="default")
>> to mimic grok.global_utility().
>> Do we need something like this?
> At the top of my head I cannot think of something that does this 
> directly in grokcore.component, so this might indeed something we need 
> to add there.

There's no such thing as far as I can see.

> Note that you can often get away with creating a subclass just for 
> registration purposes, but that does look a bit more complicated in this 
> case.

DefaultValueProvider above is an instance (with a __call__ acting as the 
adapter factory) so I can't subclass it.

>> As I've said before, I also think we should support named @adapter 
>> decorators, e.g.
>>   @adapter(IFoo, name="foo")
>>   def foo(context):
>>       ...
>> although that's slightly different.
> This is supported. See the 'function decorators' section at the bottom here:
> http://pypi.python.org/pypi/grokcore.component
> What it doesn't support is registering named adapters, I think. It could 
> be extended to do so.

That's what I meant. I know @adapter works.

> +1 from me for an effort to add these features to grokcore.component 
> (also expose them in the 'grok' namespace).

If we do, how quickly could we turn around a new release of 
grokcore.component so that I can depend on it in this project?


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

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